An Experimental Investigation of the Influence of Base Bleed on

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					                                                                       C.P. No. 892

                                                 AL AIRCRAFT ESTABLlSHMRUl

                  MINISTRY OF AVIATION


                            CURRENT PAPERS

An Experimental             Investigation          of the Influence          of
            Base Bleed on the Base Drag                           of
   Various      Propelling           Nozzle         Configurations


                 1. B. Roberts and G. J. Golesworthy

    (wifh   an Appendix by W. G. E. Lewis and M. V. Herbert)



                              Price 12s 6d net
                                               u.D.c.        No. 621-225.1          I 533.6Y1.18.OY3                       : 533.6.013.12
                                                                                                                                                c.P.     N0.892~

                                                                                                                                            Pcbrunry,      1964

                                                An experrmental lnvestrgatron   of the rnfluence                                        of
                                                     base bleed on the base drag of various
                                                         propelling nozzle conflguratlons

                                                                                              - by -

                                                              J. B. Roberts and G. T. Golcsworthy

                                     Various             propelling   nozzle         configurations                      with all-Internal         expan-

           sion wers tested                                m external         flow over the range of Mach number 0.7                                    to 2.2,

           ~.n order to determine                                the effect         of bass bleed (i.e.                         the InJectron          of low

          energy secondary air)                                  on base pressure.                                An ‘overall    efflclency’       1s

          defined,                     which enables the effectiveness                                     of base bleed,          as a means of

          reducrng the base drag9 to be assessed.                                                                 The results    lndrcate      that with

          supersonic                      external             flow base bleed generally                               tends to ra‘a1se the level          of

          base pressure,                                 but no Improvement m the overall                                 effrclency        IS obtalned.

          At subsonic                          external         speeds, the secondary air                               has a negligrble        effect     on

          base pressure.

__   E.        ..,/*m..   /*...-_I       *..    --*_l_                  A--     -   .ce--..       I    *   -1_1


               Replaces N.G.T.E.                             Report Ro. R.259 - A.R.c.~~                                228

1.0    Introduction

2.0     Doscrlption      of test   equpmcnt

        2.1       The external     flow    rrg
        2.2       Test models

3.0    Instnxnentatlon       and au       supplies                  6

4.0    Node1 pcrformsnco                                            a
                  Base prossurc characterlstlcs                     a
       :::        Overall efflclencles                             13

5.0    External     boundary layer        measurements             14

6.0     Conclusions                                                15
Acknowledgements                                                   15
References                                                         16

Detachable    Abstract    Cards



   I              Nozzle operating        condltlons



  I               Xotatlon                                         18
  II              The overall thrust efflcuzncy of il propelllng
                  nozzle vlth base bleed                           20
                  (by 8. G. E, Lowls and M. V. Herbert)


Fig.    No.                                  Title

              Model propelling        nozzls         test    rrg

              Sting   carrier     section       in tranoonio          line
              Sting   carrier     section       in supersonic          line

              General construction            of test        nozzle

              Geometry of short            and long coplanar           models

              Geometry of a&ended             shroud and boat-tail

              Geometry of base blockage models
              Locat?on of pitot            rakes for boundary layer                 survey

              A comparison of base pressure                   readings        for   short
              nozzle va;h coplanar cnt
   10         A comparison of base pressure                   readings        for long
              nozzle with coplanar exit

   11         Dase flow patterns for a nozzle with a coplanar
              exit, operating in external flow

  12-13       Performance       of short nozzle with                coplanar

   Q-15       Performance of long nozzle with                      coplanar
  16          Base flow patterns for a nozzle with                       an extended
              shroud, operating in external flow

  17-18       Performance of short            nozzle with           extended
  19-20       Construction     of the isobaric jet boundary by
              axially-symmetric      chnractoristrcs (with
              superimposed outor shroud looatron)

  21          Performance       of short      nozzle        with    extended
  22-23       Performance of short            nozzle with boat-
              talled exterior

  24          Performanoo of short            nozzle with base


FlR. PO.                            Trtle

  25-25    Comparison of results        fmm short      nozzles

  27-28    Comparx3on of overall        eff1clencles

  29-30    External    boundary layer       velocity   proflle

  31       Eatlmatcd    varzatlon   of 6': with id,

  32       Estimated    vnrlatlon   of 8 vuth Md,
                                            -5-   *

1.0     Introduction
        For the engine installation     of proposed supersonic transport air
craft, the exit area of an internal       expansion, convergent-divergent     pro-
pelling nozzle, such as would be appropriate to the exhaust pressure ratio
at 0ru1*e, often proves to be considerably        less than the cross-sectional
drea of the engine nacelle.       A relatively    large base area is thus created,
and the problem arises of minimising the dray associated with it.
Proposed methods of reducing this drag are summarised as follows?

        (1)     Base drag may be completely eliminated by extending the
nozzle until  its exit area coincides with the nacelle cross-sectional    area.
The nozzle flow will then be overexpanded at cruise, and the internal
pc3rformance will suffer.    At off-design  conditions the penalty may bo

       (ii)   The nacelle may be boat-tailed   sufficiently   to reduce the
base area to zero, whilst retaining  the correct nozzle exit area.        Base
drag is then replaced to some extent by boat-tail     drag of the nacelle.

         (iii) Base drag may bo reduced by allowing a small quantity of low
energy, secondary air to escape into the base region (this technique is
known as base bleed or base ventilation).     The exit area of the nozzle
appropriate to cruise conditions   may then be retained,   or the nozzle may
be shortened.     It has been suggested that base bleed is more effective
with such a shortened nozzle at cruise, and some improvement in internal
nozzle performance at off-design   conditions could be anticipated.
Various combinations of base bleed and boat-tailing     are also possible.

         With the intention    of helping to decide which of these systems
offers the best solution,      and more especially  to investigate the
effectiveness    or otherwise of base bleed as a technique, a series of
convergent-divergent      model nozzles has boon tested on cold dry air.     These
models lhere axisymmetric throughout, for convenience of manufacture and
testing,   although it should be remembered that for proposed supersonic
transport aircraft     the nacelle cross-section   may be square or rectangular.

2.0    Description     of test   cquipmont

        2.1     The external     flow riK

         A description     of the external flow rig used for these tests will be
found in Reference 1.          The rig consisted of two alternative    working
sections,     illustrated   in Figure 1.     Each line comprised a nozzle, viewing
section and pressure recovery diffuser,         the supply and exhaust arrange-
ments being common to both lines.          External flow from Uach number 0.7 to
1.5 could bo provided by the upper or ‘transonic’          line, whilst the lower
 ‘supersonic’      line oporated from Each number 1.3 to 2.4.       Test models were
carried on a long parallel,        hollow sting, which passod through the throat
of the test line nozzles, and could be interchanged between them.

        Figures 2 and 3 show the arrangement of the sting carrier section,
which fitted   immediately ahead of either external flow nozzle.     This
consisted of a round duct with a streamlined bullet carried on its centre-
line by a singlo hollolv arm.    From the bullet,  the sting, with the model
on its downstream end, was supported so that the outlet plane of the
model was located in the window of the viewing section.       Air, controllad

externally,      was delivered  to the model through      the                   Inner,  load-carrying
tube.       The lnstrumentatlon   and control   lines   from                    the model passed          botweon
the inner     tubo and the outer    cover of the sting.

           The transonic       line   was equipped     with a slotted      nozzle  of circular
cross-section,        Il.3 inches in diameter          (see Figure    2), tho outlet     Slach
numbor of which could be varied               simply   by adJustmg     the applied    pressure.
A two-dimensional,         flexible      wall   nozzle  vas used for the supersonic          llno,
the nozzle     outlet     being     12 In. x 12 III.     (see Figure   3).

           2.2        Test   models

         All the various            builds     of model tested         were     founded   on a common
basic  unit.    A typical            nozzle      configuration        built     from this   unit is shown
m Flgurc     4.

            The secondary           or bleed    flow was obtained        by tapping      off some of the
primary       nozzle      flow,     through    vents upstream      of the throat,        and the amount
tappod      off was controlled              by a remotely    actuated     ring valve,        located    in the
annular       secondary         passageway     between    the innor    and outer      surfaces       of the
model.         Secondary         mass flow was estimated         by passing       the air through         a
constricted          section       downstream     of tho ring valve,        equipped     with pitot
tubes and static              tappings,      as shown in Figure       4.

          Parts    additional      to those     in Figure      4 enabled      various builds      of
model to be constructed.               These builds       formed    modifications     of two ‘basic’
dosigns,      which are illustrated          in Figure      5.    Both have parallol         outer
shrouds,      orlth coplanar     exists,     and aroa ratios        of 2.050 and 2.789        (the
corresponding       design    pressure     ratios    arc 11.1     and 18.8 rospectivcly).

           Two modifications            appear   in Figure       6.     Figure        6a shows a model
incorporating           some dcgrco      of cxtornal      boat-tailing          (1'30').          In othor
respects,       this     build     is identical      to the ‘basic’          short       nozzle,    as in
Figure      53.       Figure     6b shows the construction             of a non-coplanar              (or
extended      shroud)        nozzle.       This was formed         by fitting          the outer     shroud     of
the ‘basic’         long nozzle       (seo Figure      5b) to the short             primary      nozzle    of
Figure     5s.

         For some tests   on the short    nozzle,    the base aperture      was partly
blocked.      In one such arrangement,      the bleed    flou, w&s discharged     adJaCent
to the primary    nozzle  exit  (see Figure     Ta), whilst    in another     it passed on
oithor   side of the blocking     piece (see Figure      7b).

3.0        Instrumentation          and air     suppiles

          The models were fitted      with   the following                   prossurc   instrumentation
(the circled    numbers   in Figures     4 to 7 refer      to              the location      of those
tappings,    and will   be quoted    where possible):-

           (a)       Two pltot       and two static   tubas situated      in the primary
                     nozzle    inlet,    upstream   of the bleed     flow take-off   points
                     (Numbers      1, 2, 3 and 4 in Figure      4).

           (b)        Two pitot   tubes  situated    in the primary      flow between                    the
                      bleed take-off    points    and tho nozzle    throat    (Numbers                   5 and
                      6 in Figure 4).

        (cl    Three pitot tubes and three wall static tappings in the
               bleed airflow measuring section, downstream of the control
               ring valve (Numbers 7, 8, 9, 10, 11 and 12, respectively   in
               FWP~ 4).

        (d)    A tapping   In the primary   nozzle base thickness    (Number 15
               in Figure   5a).

        (e)    A tapping outside   the primary nozzle at its outlet, indi-
               cating the static   pressure in the base region (Number 16
               m Figure 58).

        (f)    Two tappings inside the primary nozzle at its        outlet,
               indicating  the static pressure in the primary       flow
               (Xumbers 13 and 14 in Figure 5a).

        (d     Either one or two tappinge in the outer shroud base
               thickness (Number 17 in Figure 53 and Numbers 17 and 18
               in figure 5b).

        (h)    Either one or two tappings inside the shroud at its end,
               lndicatlng the static pressure in this region (Number 19
               in Figure 5a and Numbers 19 and 20 m Figure 5b).

       (1)     A tapping outside   the shroud at its   end (Humber 21 in      ’
               Figure 5a).

       (2)     Five tappings along the outside of the boat-tailed         shroud
               (Numbers 24 to 28 in Figure 6a).

       (k)     In some builds,  a reversed pi-tot   tube in the base annulus
               (Number 22 in Figure 5a).

       (4)     In some builds, a pitot tube placed in the base flow
               passageway (Number 37 in Figure 5a).

       (ml     In the models with partial  haze blockage, of the types
               shown in Figure 7, two sets of three base tappings each
               inserted in the blocking piece (Numbers 29 to 34 m
               Figure 7a).    Also, two taspings located in the constricted
               region where the bleed flow escaped (llumbers 35 and 36 m
               Figure 7b).
          Secondary mass flow was estimated from the readings of the single
pitot and static tappings located in each of three of the six measuring
section ports (Figure 4).       The averages of these readings were treated as
mean total and static pressures actmg over the constricted       passage area,
mass flow then being obtained according to one-drmensional isentropic
relations.      It is therefore likely   that the values of secondary flow
given here are over-estimated.
        The height of the free-stream boundary layer at the nozzle exit
plane was measured by attaching three pitot rakes (spaced circumferen-
tially  at 120°) to the end of the model.   Their location is illustrated
in Figure 8.

         The temperature        of the air supply          to both model and test          line
 nozzles   was maintained       within    the range 25 to 35’C at all             times.        Air dry-
 ness was measured      by an R.A.E. -Bedford          pattern      frost-point     hygrometer,      and
 held at better    than -20°C frost-point            throughout.            An supply    pressure     *as
 at a level   of 5 atmospheres         and throttled         independently      as required      for the
 modal and external       flow.

 4.0              Model        performance

                A summary of              the        operating           conditions                of    the      various      model       builds         is
 given        in Table I.

                  4.1           Base     nrossure            characteristics

            The aim of all    these tests                                 was to examine,      for each operating
 condition,     the variation      of base                              pressure    with bleed mass flow.         To obtain
 the results      in a non-dimensional                                  form,    the conventional    procedure    is to
 plot    p          against        p (see       Appendix               I for    notatron).                     In    these     tests       u is
 identical              to the         mass flow         ratio,          -QS9      since           the    total       temperature           of      the
bleed         air       is     equal     to   that       of      the
                                                                         primary           flow.

            Some caution       IS required           when interpreting            base pressure          measure-
merits.         As mentioned      in So&ion            3.0,     a variety      of pressure        tappings        was
provided        in the base region           of these models.                In many tests,          particularly
those on the short           nozzle       versions,         these    toppings       indicated       uniformity          of
base pressure         for low quantities               of bleed flow,          the agreement         steadily
deteriorating         as the bleed flow incrcssed.                        A typical        set of base pressure
readings        is presented     in Figure          p for the short            nozzle     with no boat-
tailing       and a coplanar        exit,      and Figure         10 gives       a similar       comparison         for
ths long nozzle          with coplanar           exit.         In the latter          cast,    the spread         at
high blood        flow rates     is much worse.

         For tho purposes         of comparing        model performance         one with another,                                                         it
is necessary    to assume a single           bosc prassuro       characteristic         for each
build.      The base pressure        results      which follow     have accordingly         been
obtained    by averaging       the available        readings   at each bleed        flow value,
despite   the large     differences       occurring       in some instances.

          Before                considering            the      expcrimontnl                results   in dotail,   some des-
cription     will               be given        of     the      variations            in     flow pattern    which are

               The flow in the base                          region        of a propelling                  nozzle           with a coplanar
exit     is     shown diagrammatically                            in     Figure   11, for                supersonic             external  flow
and various                  operating        pressure            ratios.             In Frgurc                11 a we assume          g      < 1p
so that     the external          stream      expands     around   tho lip of the outer             shyoud
(at A).         Also,     in this      example,      the flom within          the primary      nozzle     is
under-expanded,           and so continues           to expand at the nozzle            exit     (at B) rn
a similar       manner to the cxtornal               stream.       Clearly,       the ex t e rnal and
internal      boundary       layers      (of thicknessi;         6~ and 6I reopoctivoly,              as sholm
in Figure       Ila)    must detach         at A and B, and free            shcor layers      will     develop
in the regions          A-C and B-C, dividing              the stagnant        base region      from the
supersonic        streams      on either       side.       At G, the two shear layers               evidently
converge      in a recompression             region.

               If   sufflciont          blood      flow     is    now inJected           to    cause -    to exceed
    unity,     the expansion            at A is       replaced          by a shock,           and the flow pattern                   is
    modified      to Figure         Ilb.

            Alternatively,        if the pressure      ratio     across   the nozzle      is loworod,
 tho expansion          fan at E may be replaced         by a shock,      and the flow pattom
 wll     then be as Figure          11~.   Further     reduction       in nozzle    prossurc     ratio
 may cause the internal             jot to separate      from the walls,        thus effectively
 lncroasing       the width     of the base.        The approprratc         flow pattern      for the
 scparatod       condition    is shown in Figure         Ild.

          V!ith subsonic  external    flow,    the expansion         fan                             or shock ot A is
 repiaced     by a zone of gradual    expansion        or compression,                                  and the rccompres-
 sion region     at C may bc expected       to exhibit     difforcnt                                 characteristics,

          Figure    12 presents      tho performance         of tho short       nozzle     with a
coplanar     exit,   in supersonic       external    flow.        The flow pattern           hero is
evidently      of the typo dcpictod         in Figure      Ila.      Small quantities            of bleed
flow (around       2 per cent of the prrmarJ           mass flow)       result     rn a significant
incrcaso     in base prossurc        (some 40 por cent),          but little       further       improvc-
merit is realised       with higher      quantities      of bleed flow.            For values        of n
m CXC~SS of 5 por cent,            tho bass pro ssuro          is sensibly      constant.
Figure    12 also    indicates     that a reduction          in exhaust      pressure      ratio
    E.P.R.     = 2         causes a fall           in the lcvcl            of base prossure                ratio.
i                      >
             The bnso pressure               chsractcristics               of the same nozzle                  in transonic
 and subsonic            external     flow are given               in Figure           13, for values of E.P.R.
 appropriate           to a supersonic             transport         aircraft         operating          at thcso         flight
 conditions.               In the case of &,,=                 1.1 (Figure           13a), reduction              of E.P.R.
has resulted             in on increase           of bosc pressure                 lcvcl.          This trend           is clearly
 opposite        to that       observed       in Figure           12, whcrc tho external                    Mach number and
E.P.R.       were higher.             An effect           of this        nature       is consistent              with tho
 results       quoted        in References           1 and 2, which indicate                     that,      for a particular
external        Mach number,          n critrcal            value of E.P.3.               exists       at which tho base
pressure         ratio       16 a minimum.             Ghcn E.P.H.            is reduced           below this           critical
value,       the base pressure              ratio       incroasos         rapidly;           above it the bsso prcs-
sure ratlo           rums      slowly     with lncroase              of E.P.R.             Reid and Hastings2,                    work-
mg only at L&,= 2.0,                  attribute           this     dlscontrnuity             to a change of tho
recompression              shock pattorn          in the oxtornnl               flow at C (Figure                 Ila),       but
Reference          1 shows a very similar                   bchavlour         of base prassuro                with change
of E.P.R.         in subsonic         external         flow.

         A consideration       of               Reynolds      number suggests       that   the primary                       nozzle
boundary   layor    is turbulont                   throughout,for         the conditions       of those                    tests.
At E.P.R.    4 in Frguro lja,                    the nozzls       applied    prcssuro    ratio
   A.P.R. = pt     varies    from 5.8 to 5.0,                          and the      nozzle         should     thcrcforo         be
(             pb >
 running  full.       This will,    of course,                         also    be true        at    any highcr         E.P.R.
The flow pattern        than rcscmblcs   Figure                         Ilc.

               In the case        of Figurerelating     to an external
                                                     13b,                     Mach number of
0.69,        base pressure          ratio  to bc romarkabl
                                            is       soon           indopcndont      of both
bleed   flow rate and E.P.R.,      the gcncral      1~01    of -      being around       0.9.
The flatness     of those curves     is apparently      associated       with the prcsonco
of a subsonic     external stream,     a rslatron     borne out by other          results     to
                                                            -   10 -

be mentioned      later.      Just the same effect         has bccn obtained       at 0.N.E.R.A.4,
using  a baso blood       modol very similar        to that   shown in Figure       5a, with an
aroa ratio      of about 2.6.      Furthermore,       roccnt   theoretical      work by Nash3
does in fact predict        that base bleed       is likely    to bo ineffective        in sub-
sonic  external      flow at those values       of Reynolds      number.

           Performance        of thG long model with a coplanar                 exit   is prcsonted      in
Figure     14, for external         Mach Numbers of 2.2 and 1.8.                   Those base pressure
characteristics           have a difforcnt      shape to those           discussed     carlicr,     and the
reason for this           is not closr.        Howcvor,     the senso of variation              of base
prossuro      ratio     with E.P.R.     is similar      to that      obscrvod      in the short      nozzle
results.          In Figure     15, the porformancc         of this       nozzle     at subsonic     speeds
18 glvon.           Hcrc again,     the trends     are similar         to those obscrvod         for the
short    nozzle,       and baso blesd      is clearly     ineffective.

           Shown for comparison             on Figures        14 and 15 arc some data extracted
from    Rofercnce       1.       The nozzle     tharo     had an aroa ratio            of 2.90 (dosign
prossuro      ratio     20) and a thin base, without                bleed.         It 1s intoresting         to
note that,        for the case of zero bleed               fiow,     thsre      is fairly      close general
agreement       botwccn      the values      of base pressure           ratro     obtained      from
Referonce       1 and those        from both      ‘basic’      models in the prcsont              tests, dcs-
pito    quite     large    differences       of design       pressure       ratio    and base height
(comparo      Figure      12a with     14a,    12b with       l&b and 13b wltii           15b, for matching
conditions        of C.P.R.).

           Now if the base region          were able to be shielded          from tho cxtcrnal
flow,    it is reasonable       to suppose      that the benefits        accruing   from base
bleed    might be increased.            This should       be ospccially     so in the case of                                 a
shortened      primary   nozzle    at cruise      conditions,      where the internal     static
pressure     in the cxit     plane    is higher      than ambient.        To this   end the
extended     shroud    mod21 of Figure       6b was tested.

            Figure         16 depicts         the flow pattern             in the base region             of tho
cxtendod       shroud         system,       for supersonic           extsrnal       flow and various              nozzle
operating        conditions.                In Figure         160 the operating             prossurc      ratio       is
sufficient          to cause the internal                  flow to expand at the primary                      nozzle
oxlt     (A).         A frso       shosr layer          develops       in the region           A-B.       Subsequently
tho Jet reattaches                 on to tho outer             shroud     at 9, with accompanying                   recom-
prossion.            At tho same time,                the free shear layer                is rehabilitated              on tho
shroud      to form a nGw boundary                    layer.         Finally,       further        expansion        or com-
pression       will       occur at C, dopending                 upon overall          conditions.             Clearly,        In
this     case, ths base region                    1s completely          ahioldod       from tho external               flow.
So far as the internal                   flow is concerned,               base pressure            theory     (e.g.
Rcfcrsnoe       5 relating            to backward-facing               stops)     indicates          that   a reduction
in E.P.R.       may be expected                 to result       in a proportional              lowering       of the
base pressurs             ratio,      the A.P.R.         remaining        constant        for a given value of
I”, provided          always      that      the prim&rJ         Jet reattaches            on the shroud.                This
1s sayrng       no more than that                  the region       A-B-C in Figure              163 beOOmGS
cffoctivcly           part of the internal                 expansion        system,       controlled        only by
tho pressure            at C.

          Corresponding       to Figure    16b would be the casG when applied          condi-
tions   are the samG as for Figure            16a, but the shroud    length     IS reduced     so
that rcattachmcnt        cannot     occur.     The recompression   zone will      then lie
outside    the nozzle,       and buhaviour     ~11 be similar    to that    already    described
for the coplanar        exit    models.
                                           -   11 -

          At low values of A.P.R., the expansion at A is replaced by a shock
 which tends to deflect the internal     flow away from the shroud, and ~111
 eventually    prevent reattachment regardless of shroud length (Figure 16~).
 St111 further reduction of A.P.R. gives Figure 16d, in which the internal
 flow is fully    separated within the primary nozzle.    In all these cases
 the external flow is able to influence ccndltions     in the region A-C, so
 removing the immunity of base pressure to external flow enjoyed when
 reattachment takes place within the shroud.

           At conditions when the external flow is subsonic, the internal
 situation    will generally resemble that in Fq,ure 16d, with no reattach-
 ment.      The system is therefore likely to behave in a manner similar   to
 the coplanar exit models, which were then insensitive     to bleed flow.

         It can be realised from the foregoing discussion that, for an
extended shroud model to operate efficiently       at cruise, the shroud should
be long enough to permit internal    reattachment.      The critical length will
depend upon the value of base pressure created in the region A-B
~;;-,‘54      t which in turn is affected by the amount of bleed flow

          The results of tests on the extended shroud model are presented
  in Figure 17, for supersonic external flow and various valuee of
 E.P.R.      %hen - pb is plotted against J.I, the same results fall fairly            close
 to a single curve (Figure 18), as would be expected if sufficient               shroud
 length were available for reattachment to take place throughout the range
 of bleed flow.

          For sero secondary mass flow, p ‘b = 0.036.            If the internal     flow
                                                pt. baoh number at the primary nozzle
 is assumed to be inviscid,        then once t e
 exit is specified,      the position of the jet boundary streamline may be
 calculated by the method of c aracteriotics           (in this case for axisymmetric
 flow).      A computer programme % has boen written for this purpose, and the
                            % = 0.036 1s shown m Figure 19.
 result obtained when -                                                In this compu-
                           PP t
 tation,   the outer shroud is assumed to be absent, and the boundary of the
freely expanding jet 10 dotormined.             The external shroud location 1s then
 superimposed on the drawing, to give an approximate indication             of the
minimum length for reattachment.           Viscous effects will introduce some
modification      to the picture.      At eero bleed flow, the shroud is of ample
length.       The corresponding flow pattern for - Pb = 0.085 (corresponding
                                                        PP, t
to n = 0.08) appears in Figure 20.            In this case, It ~011 be observed
that the outer shroud, no matter what its length, cannot contain an
inviscid    free-jet.      However, m the presence of secondary flow, the
reattachment streamline       can no longer be assumed to coincide with the
inviscid    jot boundary.       This could mean that tho picture given by
Figure 20 is to some extent pessimistic.              The scatter of the experimental
points in Figure 18 at higher bleed flows may be due to partial              failure
of the primary Jet to reattach.

        Values of base prossure ratio obtained with tho oxtendod shroud
model in subsonic external flow are given in Figure 21.    In their ‘flat’
character these curves resemble those for coplanar models, as previous
consideration  of the flow patterns suggested.
                                             -   12 -

         Test results for the boat-tailed   model of Frgure 6a are shown m
Figures 22 and 23.      Figure 22 is for Ma 2.2 and 1.8.     These curves
exhibit a maximum value of base pressure ratio at bleed flow rates varying
between 4 and 6 per cent.      The pronounced fall in the level of base pres-
sure ratio at high bleed flows is thought to be due to the increased velo-
oity at which the secondary air is discharged through the constricted     bass
passage.     Figure 23 relates to transonic and subsonlc external flow, and
comparison with Frgure 13 for the 'basic' short nozzle shows little
difference   as a result of boat-tailing'at  these conditions.

           Before any test data became avaIlable from other builds,     some
 opinion held that the performance of the short nossle with P coplanar exit
mrght be improved by introducing       partial blockage in the base region, and
 causing the bleed air to be discharged at high velocity.         The models
 illustrated     in Figure 7 were accordingly  tested at & 2.2.     Figure 24
 indicates    that the high rnJection velocity    of the bleed air has In fact
produced the opposite effect to that required.          As can be seen, tho base
pressure ratio remaans either almost indopendcnt of bloed flow, or actually
falls with increasing flow.

          In Figure 25 is presented a comparison at M',2.2 between the base
pressure characteristics     of all the mAdo builds with a short primary
nozzle.      It 1s evident that the extended shroud model makes much the most
offcctivo    uso of bleed air.     At low bleed flows, the boat-tailed   build is
superior to the 'basic' short nozzle, although inferior        to the oxtended
shroud.      This advantage disappears at larger bleed flow, when the velocity
of blood discharge becomes too high.         Still greater discharge velocltios
occurring in those models with partial      base blockage are clearly

          It should be borne in mind that some further drag is associated
with the boat-tail.       This component is included in the overall thrust
efficiency,    to be discussed in the next Scctlon, and was derived from pres-
sures measured on the boat-tail     surface.

        A srmilar comparison is made in Figure 26 for three builds with a
short primary nozzle at b&,0.7.   No si@rficant   differences can be

         To sum up the effects of gcomotry and bleed flow on base pressure
ratio   alone, without regard to the overall picture,  it IS apparent that:-

         (1)     Elced flow can increase base pressure ratio in supersonic
                 external flow, rapldly at first  and subsequently more
                 gradually,  so long as discharge velocity  is low.

         (ii)    Boat-tailing    as a general            principle     offers      some improvement
                 ln SuperSOnlC    eXtCrna1       flow,       SUbJeCt    to   (1)    above.
         (iii)   An cxtcndod shroud, of length sufficient     to allow reattach-
                 ment of the primary Jet, successfully    shields the bleed
                 discharge from a supersonic external stream, and permits
                 much higher values  of base pressure ratlo     to be attained
                 for a given bleed flow.    The effect IS particularly
                 marked at high bleed flow.
                                           -   13 -

        (iv)    With subsonic external flow and appropriate primary nozzle
                operating conditions,  the value of baso pressuro ratio is
                virtually constant regardless of bleed flow or geometry.

        4.2     Overall   efficioncios

         To enable the performance of the various nozzle configurations      to be
compared directly,    a form of ‘overall  efficiency’   (n) has been employed.
The expression for n is given in Appendix II.         This enables base pressure
characteristics    in terms of i;- versus n to be converted into efficiency
characteristics    (i.e. q versuzu) , which provide a true measure of the
effectiveness   of base bleed as a method of reducing base drag.    It should
be noted that in the derivation    of the efficiency expression, it is assumed
that the secondary air is captured at free-stream    conditions, and its
inlet momentum has been computed on this basis.      This momentum tenn can
be very important at high bleed flows.
          It 1s unnecessary      to convert all the base pressure data into
efficiency    characteristics,       since it has already been seen that the base
blockage modifications         to the short nozzle proved unsatisfactory.
Furthermore, it has been observed that the performance of the short nozzle
is considerably     improved when the outer shroud is extended, and so it only
remains to compare the following          configurations  on an efficisncy basis:-

        (a)    short nozzle with         extended shroud,

       (b)      ‘basic’   long nozzle with       coplanar   exit,

       (cl     short nozzle     with boat-tailed      exterior.

         In figure 27, the overall efficiency   of these three configurations
is plotted against the bleed flow ratio p for l&,2.2 and E.P.R. 20.          The
corresponding characteristic   for the ‘basic’ short nozzle with coplanar
exit is included for comparison.      These results reveal the following
points of interest I-

       (i)     For both the ‘basic’ short nozzle with coplanar exit and
               the boat:tailed    model, the inlet momentum of the secondary
               air becomes a dominant factor in the expression for n
               as bleed flow increases, which the rise of - with n is
               insufficient    to offset.   This causes n to fall as u

       (ii)    As the base pressure characteristics     would lead one to
               expect, the efficiency    of the extended shroud model is
               markedly better than that of the ‘basic’ short nozzle.
               In this case, tho rapid increase of F with p at low
               bleed flows is sufficient     to OvercomeOOtheeffect of the
               secondary inlet momentum and the efficisncy      mcreases
               slightly  up to a value of u = 0.02, whereafter it falls.
               The maximum efficiency    is, however, only marginally
               better than that at zero bleed.
                                                      -   14 -

            (rrl)      The best effrcrency            1s obtarned        with    the    ‘basic’     long
                       nozzle  and no blood.

           On Frgure     27 1s also shown a value of n obtarned                     from Reference     1
for a nozzle       of design     pressure      ratlo     20, wvlth a thin base and no bleed,
operating       at the same condltlons.               This nozzle      had a value        of overall  area
ratlo     (maxrmum cross-sectlonal           area/throat         area)   of j.06,      as compared   with
3.39 for the present          models.        It should be noted            that   the efflclency
values     quoted    In Reference      1 ordlnarrly         exclude    the drag force        on the
annular     base.       For comparison      with      the overall      efflclancy       used In tho
present     tests    (Append=     II),    It 1s necessary           to deduct     the base drag term
as given      m Reference      1.

         Slmllar   comparrsons     to that    1n Figure    27 have been                     made for       various
values   of %.P.R.    and external     hfach number.      At supersonIc                      external        speeds,
the trends     arc consistently      as lndrcated     In Figure   27.

           It ~111 bo observed             that     the nozzle   tested In Reference  1 has a
hrgher     efflclency     at cruise          condltlons     than any of the base bleed   models
considered        In this   report.

           A typical     comparison     with subsonrc      external flow (I&,=     0.70,
E.P.R.     = j) 1s shown In Figure          28.    It ~11 be observed         that under   these
condltlons,       nono of the models bcneflted           from the lntroductlon       of base
bleed,    n consistently        fdlllng    as n I.S Increased.      A corresponding      value
of q obtalncd        from Reference      1 1s agarn mcluded.

5.0        Extrrn,al     boundary      layer     measurements

           Theoretical     work3 lndlcatcs        that    the level      of base pro-sure     achieved
In tbs       type of oxperrment       IS Influenced,         to a great     extent,    by the thick-
nesses     of the rntornol        and sxtcrnal      boundary     layers.       To provide    a datum
for tile test results,          It 3.6 therefore       necessary      to measure or cstlmato        the
approprratc       boundary    laycr   parameters.

           No attempt    was mado here to take                   measuromonts       of the lntcrnal
boundary     layor.      A method of estrmating                    boundary   layer    thlckcess    In       a pro-
pcllrng     nozzle    may be found In Appendrx                   IV of Reference       7.

            The external        boundary       layer     In the model cxrt         plane was explored              by
means of the pltot            rake dcscrlbod           In Section        2.2.     Cxperlmcntal        velocity
profiles       were found to be lndepcndont                    of free-stream      Mach numbor,        and the
results       were therefore        averaged.            Vcloclty      profiles    obtalnod       In the
12 m.‘x        12 In. supersonIc           line     and the 11.3 m. transomc                 llno   aro dls-
played      ,n Frgures       29 and 30 respoctlvely,                where they arc conparod            nlth      one-
ninth    and one-eleventh           power law profllcs.                  It wrll   be observed       that      the
expcrlmontal         results     do not conform            to clthcr       of these power laws.             The
approprlatc        boundary      layer     thlckncss         for the supersonrc         line     was 0.80 m.,
whrlst     for the transonlc           llnc      It was 0.62 m.

           These values      amount to 23 per cent and 18 @r cent respcctrvely                             of
the overall       model diameter.         For comparison,          the englnc       nnccllc      of a
supersonIc      alrcraft     might be expected         to grow a boundary           layer    around
12 per cent of Its diameter            by the nozzle        outlct      plane.        For a g-lven
aftcrbody      gcomstry,     this  ~mpllos      that    tho ratlo     of boundary        layer     thick-
ness to base height          1s unropresentntlvely          high In the present             work.         On
the cvldcnce        of Reference    8, there        IS In consequence          a goneral      tendency
to over-estimate         base pressures.
                                                    -   15 -

         By assuming       that  the total    temperature     throughout    the boundary   layer
18 constan<,      It 1s possible      to calculate,       for a given external     Mach number,
the displacement       thickness    (o*) and momentum thickness          (f3) from the experi-
mental   velocity    profile.       Variation       of these quantities     with LI, is pre-
sented   in Figures      31 and 32.

6.0        Conclusions

         In most of the nozzle        configurations              which were tested,           base bleed
was observed      to raise  the level      of the base            pressuro    ratio,        so long as the
external     flow was supersonic     and the nozzle               was running       full.        When the
external     flow was subsonic    and appropriately                low pressure         ratios    mere
applied    to the nozzle,     base bleed was found                to be consistently           ineffective.

            On comparing      the results           in terms of an overall         efficiency,      and
debiting      ths fres-stream          inlet      momentum of tho bleed       air,       it is found that
no significant        increace       in efficiency          can be obtained    by em@oymg           bass
bleed     in any of the configurations                  under any conditions.              It would appesr
that     base bleed does not afford                 a gonor     method of improving            the perform-
ance of a propelling            nozzle       insta113tion.

          There is dcfinitoly      no case for cutting        short     tho internal         expansion
surfaces     of a nozzle    in order   to provide     an aren for introduction               of baso
bleed.       In the case of a long-range        transport     aircraft,      better     all-round
nozzle    performance    can be obialncd     by continuing        tho primary       expansion       at
least    as far as is required       to reach ambient      pressure       at cruise.

         The authors        wish to acknowledge           the assistance         given    in   this   work    by
Mr.   C. Overy,  Nilss      EL Falers  and Kiss          V. Soarle.

          This experimental             investigation        was undertaken        at the request       of the
British     Aircraft       Corporation,         viho designed     and built      the test models.            Tho
experimental         work was carried           out at the National         Gas Turbine       Cstablishment,
and the results          presented        m this      report   have been independently            asscssod.
Figures     l+ to 8 have been taken from the ralevant                      dosign    drawings,      with ths
kind permission          of the British          Aircraft     Corporation.
                        - 16 -

                                           Title.    etc.

1   G. T. Golesworthy      The performance of a conical oonvergent-
    M. V. Herbert          divergent nozzle with en area ratio of
                           2.9, in externel flow.
                           A.R.C. c.p.891
                           November, $963

2   J. Reid                The effect of a central          jet      on the base
    R. C. Hastings         pressure of a oylindricsl              sfterbody in
                           a supersonic strenm.
                           A.R.C. R. & M.3224
                           December, 1959

3   J. F. Nash             Private   communication     1963

4   P. CarAre              Unpublished work at O.N.E.R.A.
    M. Sirieix             Ch&illon-sous  Bagneux, France,              1763

5   J. F. Nash             An znnlysis of two-dimcnsiond    turbulent
                           base flow, including  the effect of the
                           approaching boundary l.ver.
                           A.R.C. R. & ht.3344
                           July, 1962

6   J. B. Roberts          Unpublished   work at N.G.T.E.            1963
7   11. V. Herbert         The design point porformctncc of model
    D. L. Mertlew          internal  expansion propelling nozzles,
                           with area ratios up to 4.
                           R.R.C. R. & Ia.
                           December, 1963

8   G. T. Golesnorthy      The perforwnce    of conical convcrgent-
    J. B. Roberts          divergent nozzles of area ratios 2.44 and
    c. Ovary               2.14 in external. flow.
                           S.R.C. C.P.893
                           February, 1964
                                       - 17 -

                                       TABLE I

                             Wozzlo operztmg     condltlons


             J3od.01build            Mach No.         Exhaust        pressure            ratios

;     Short nozzle wth                 2.20          20.44,       15.52
      coplanar exit                    1.80          14.92,       12.19
                                       1.10           7.01s        4.05
j/                                     0.69           5.66,        3.01

;’ Long nozzle wth                     2.20          20.52,       18.45,        16.45
   coplanar exrt                       1.80                       11.75
                                       0.89          yji,          3.01
                                       0.70           5:07:        2.96

   Short nozzle with                   2.20          20.01,       11.94,        15.94,            14.02
:/ oxtondcd shroud                     2.01          19.96,       17.98,        15.91,            24.03
                                       0.88           6.06,        3.02
                                       0.70           5.06,        3.02‘

      Short nozzle wrth                2.20          19.50,       17.84, 16.00,                   13.95
I     boat-tollmg                      1.80          14.95,       12.00
I                                      1.09           1.12,        3.97
                                       0.70           5.00,        3.00
      Short nozzle mth partml          2.20          19.95,       17.95,        16.25, 14.40
j     base blockago - typo (a)
S‘ _                             1
j’ Short nozzle wth partml             2.20          20.05,       17.95,        15.50,        14.02
    bsso blockage - type (b)
 ::                                                  _-       -                                           -.
                                                     - 18 -

                                              Ayp~mIx            I

A              cross-sectional            area
D              drag force


P              pressure      (st&tlc         unless           otherwise      stated)
Q              mass flow
R              gas constant        for       xl.r (= gel ft             lb/lb%)
T              temperature         (static       unless          othermse          stated)
v            , velocity

a              primary      nozzle       divergence             half-angle

P              afterbocly     boat-tail          engle

6        .     boundary lay&             thickness
60             boundary layer            dwplacement                 thickness
e              boundary layer          momentum thi&ness

rl             overall      thn&         efficiency             of nozzle         and bleed system

               (see Appendix II)

               primary      nozzle       internal         gross tllot              efflclency
               bleed a~       momentum efficiency

IJ             bleed mass flow ratlo                 (’= Qs%
                                                      \        ?PRp,t


                                                               Primrf       nozzle entry total       pressure
E.P.R.         Exhaust pressure              ratio        =                  Ambient pressure
                                     -    19 -

                                   AITm1x        I (cont'a)

*     isentropic       conill+aons       111prunery nozzle throat
b     base

e n0wJ.e exit

m     maximurr, cross-section            of nacelle

n     cross-section       of nacelle        at ex3.t plx~e

P     primary      nozzle flow

s     secomla-y      or bleed flow
t     tot&l      head condltiona

E.T   boat-t&l

co    amblent condxtions
                                                                  -   20 -

                                                           _- _
                                                           --                  11

                    The overall
                    _-------            thrust         ef'ficlency of a propellmg                 nozzle
                                                       with base bleed

                                                                  - by -

                                       Y. G. E:. Lewis and M. V. Herbert

    Case A.          Conical         prunary     nczzle           running        full.

    -fe shall       define       the following             fcrce       terms:-
                =    momentum + pressure                   thrust            of pruner    au   at primary      nozzle


    Fs          = momentum of bleed au                       at outlet              + base pressure   thrust

                =   11,   *-g--+        :A,-      &)        @I,       -pm)                                          ..“(2)

    Da          =    Inlet momentum of bleed au,                               assumed to bc taken from
                     free stream

                = Qs%                                                                                               . ...(3)
                =    boat-tall         drag of nacelle                  afterbody

                = (il, - A,) (pm- PB.T)                                                                             . ...(4)
                                                            -    22 -

    the signs being taken such that

            Total        force        =      Fp + Fe - De - 4-T

    We further      define

             p,ldeal             =       g

    where Vis is the fklly-expended                      rsentropx          velocity           correspondir&        to

            -p" t        ( = E.P.R.)

    The overall      efficiency              is given by

                         I'      + Fs - Ds - DB. T

    It IS oonvenlent              to express ell         force    quantities               non-dlmenelonelly         in
    the f 0x-m

            Fp , ideal            =   !pL                                                                            .. ..   (5)
                 AQP,t                         J.PI',t

    where   %       = AVp,t

                                                                                                                     . . . . (6)
                                                                            ,J,.- ...          E.E'.R. 1

    where         the isentropu       veloolty  corresponding                          to prunary
                                                  A,     2
                              nozzle area rat10 -A* ( 1 + cosib )
                                                                                                           p t
             D.P.R.           is the primary         nozzle deblgn press UT0 rat10                       = -p

                              is the design-pomt            efflcxncy                   of the prun~!f     nozzle
                                                          -   22 -

Nwi                             8,RT,
                       vs   = A&

and putting             p   =   Q&i-

               Q 1'             I-I~K~'R    ~ (-@Pp,t)a        , T,
we    get     .2.2=
                 g                    g          *34,            Ta,t

.D                                                 .-.


              D               Gp            %a
                            = -.-                                                                . ...(a)
            *"Pp,t              "G

                                                                                                 . ...(Y)

                                           (6) + -- - (8) - (9)
Thenq       1s evaluated            as

1.          PB.T may be determuwd apprrximately     for a given boat-tail     angle 9
            by using the appropriate  two-dimenslonal   Prandtl-Meyer   relation,   or
            from experimental pressure measurements if available.

2.          In the present tests Y for all                      three   streams can be taken as 1.4,
            SO that Kp = 0.3966.

3.          In (7) and (8) It will usually be pussible t? write Ts,t = Tm,t.
            It2 these particular tests It 1s true tc put Tp,t = T,,t = T",t*

4.          In many cases It ~11 be suffxlently      accurate to take
            Ts/T3 t c 1 in (7), the first   term of which amounts t,) a very
            small'part   of the wtile fzce.     For the same reasonns 1s also
            taken to be unity in the absence of other wf'ormat~on.

5.          If the velocity   of bleed air discharge 1s sufficiently    great for
            the approximation   in Note 4 to be urqustifled,   the value of Ts/T3,t
            can be fgund as follows:-
                                                                 -     23 -

                 T                         Y -1
           while +                =    1 + -+             Ias"

                    uT            Ts,t ,              =      Lg.                c!gz      ($(A.P.R.)
                         s    (   Ts        1                          s                     s

6.         The value of prmsry                  n~zzlc               design-paint        effu?iency'~,mBx         depends
           on D.P.R. and cone angle c,,                                It may either *be calculated   approxi-
           mately or derived from static                               thrust calibrations.      For the primary
           nozzles of these tests, vnth                               a = IO0 and D.P.R. values 11.12 and
           18.76, a fqure   of 0.988 was                              estunated from Reference'     as a~prop-
           riatc to these test corxiltlons.

7.         II' the primary nozzle should be other than conical,   e.&. two-
           dimensional,   the same relations are applicable except as regards
           the te,rms %),max d                  1 + cosa                   *

Case B *
--.           Conical         prunary nozzle wzth internal                              separation,

Relatwns    (2), (3), (h), (5), (7),    (S), am3 (9) remain as l~1 Case A,
ad Notes 1 to 5 apply.      Alternative     treatment must, holvever, be used for
the qwntlty     F when the prxmary nozzle is no longer running "1.
Ve ml1 now wrEte

           I”P[2P.I -%J
             =5gi, +
                  L1          &+==
                                                p,t        i~R
                                                                                * .;*
                                                                                            . * *
                                                                                                  >     ....    (IO)

where                        1s the isentroplc                       velocity     term corresponding


           to f$$    (= A.P.R.)

           1s the internal efficiency    measured for the primary                                      nozzle    opcratm@;
-9         under stntxc condltlons    at thus value of A.P.R:

Then q 1s evaluated               a~~")         + (7) 5r (8) - (')
                                       -   24 -                         Report No. R.259


8.      To take an example, appropriate          to curve 2 of Figure    28,   for which

                h$$ = 0.7;   E.P.R.   =    3;     D.P.R.   =   11.12

        we see from Figure 13 that Pb/p, a 0.9, giving A.P.R. = 3.33.   At
        thx condition a suitable value of % would be 0.92 with turbulent
        boundary layer separation.

9.      It 1s worth observing that any          primary nozzle of sdar     geometry
        but different  D.P.R., provided         that turbulent separation still
        occurs at the same A.P.H., wiLl          have a value of
        tion quite close to that given          111Note 8 above. 'TZL3%L"Z$~e
        understood by reference to the          sketch below, d.ra%vnfor a partzcular
                                                     a     b       o



        Due to the nature of the pressure riso occurring in a nozzle with
        turbulent boundary-layer     separation,    most of which is concentrated at
        the separation point as depicted,        it will make very little     difference
        to the internal    performance, as represented by the shaded area, whether
        the nozzle ends at station a, b or C. For instance, e,t the condition
        of A.P.R. 3.33 with a turbulent boundary layer mentioned in Note 8, a
        IO0 nozzle of D.P.R. 20 has ?jp = 0090 (Refs. 1 and 7),           as compared
        with the value 0.92 taken for D.P.R. ?1.12.         It is therefore generally
        unnecesscxy for work of the present neturz to carry out static thrust
        calibrations    for every nozzle of different     D.P.R. encountered.

IO.     In the special cx,e of no bled flow (cl = 0) an< no boat--tail
        (P = 0), the expressIon for overall.effudency  reduces to
                                            -       25 -

        It my be noted that, rmth the, further condition     of 41 = A,
        (zero base thickness),   this reduces to the famllxr    symmetrical
        ralatlon for angle-stream     nozzle internal performance

                                  F-    E.P.R.

        m whxh     the notation     is now as used, for        mstmce,   in Reference 1.

D 76932/l/125875     I& IO/'66    R & XT,
                                      FIG. I

                                                      FIG. 2


                                                 OF    NOZZLE

                                                 INLET    OF
                                        ’        SLOTTED


                      I                FIG. 3



                                                                    FIG. 4

                     I                         /PRIMARY                 NOZZLE

                     c                         /OUTER                 SHROUD


                                               ~~~NN~JLAR               hmst.m~~c

                                                             SECTION        MVIDED
                                                            INTO      SIX         PORTS

                                               i                  PRI MARY        PITOTS

                                               F           RING     VALVE

                     7-                        .-
                                                           INLET     PITOT

                                                            UTER      STING        TUBE

                             INNER’    STlNC        TUBE

   GENERAL   CONSTRlJCTlON            OF       TEST                 NOZZLE.
                                    THROAT    DIA.       I.90

                                    PRIMARY    EXll     DIA.         2.720

                                    SHROUD    OUTYDE           DlA    3510

                                    THROAT      DlA     I.90

                                    PRIMARY    EXIT      DIA         3 172

                                    SHROUD    OUTSIDE           DIA 3.510


                                                        FIG.6 (a a b>

                                           THRQI\T     DIA                        I .90’
                                           PRIMARY      EXIT      UA.            2 720”
                                           SHROUD      OUTSIDE          DIA.      3.275”


                                                     THROAT      DIA.                 1.90”
                                                     PRIMARY     EXIT     DIA.        2.720”
                                                     SHROUD      OUTSIDE         DIA. 3410”

                                                     SHROUD       OVERLAP              I, 268”


GEOMETRY           OF       EXTENDED    SHROUD           8 BOAT-TAIL

                                           FIG.7(0 L b)

                           THROAT    DIA             I. 90”
                           PRIMARY    EXIT DIA       2.720”
                           SHROUD    OUTSIDE     DIA 3.510

                                   FIG. 0

                                                                                      FIG. 9

 pb                                                                               0



     0,                                -                    I

                                                         ?.A,=2   20
                                                         E P R=IS.SO



                                                            I            I
                                  LOCATION          OF STATIC          TAPPINGS


                                             AXIS   OF   NOZZLE
     0              --           --                                          --


         0   ____

                         0   2          O-04              0.06         0 08

   FOR SHORT                          NOZZLE WITH COPLANAR  EXIT.
                  A                                                                            FIG.   IO
       2       o-
 - ‘b
                                  1   LOCATION              OF         STATIC   TAPPINGS
           I   e-

           I 6-

                                             _ AXIS       OF-    NOZZLE     _

       I       4-                 I


      1.;                  Me         =   2.20
                           EPR        I   18.45


                                                      4          D



 04                 --


                           0.02                   0                0

A COMPARISION                                 OF BASE                     PRESSURE         READINGS
   FOR                   LONG             NOZZLE                  WITH          COPLANAR      EXIT

     08 l-



                                                                          0 E P R.=20.44
    04                                                                -   x EPR    =I5       52



          0 L
               0        2      0   k4            0       6   0        3       0    0              P
     IC A-


    08    ,-


               !                                                          X EP.R       =I4   92
    04                                                            -@EPP                r12   19


                   0   12     0    14        0       6       0   08          0.    0              P
    PERFORMANCE                 OF SHORT     NOZZLE                                WITH
                            COPLANAR   EXIT.
                                                               FIG.          13(ae       b)


                                                                 m ERR-7     01
                                                                 a E PR14.05


      C                                                                 I
                  ,D.0 2   0.04            0 06       c   BE          0.10





0.4                                                       -      Q E.PR -5.66
                                                                 X E P.f?=3 01

                                   hi#O   69


      0            L
          0       CIC )2    0.04               0.06   0   1s          0.10

PERFORMANCE     OF SHORT NOZZLE                                         WITH
           COPLANAR   EXIT.
                                                         FIG.          l4(a       a ti

                                                         x E P FL=     20.52
                                                         0 E.PR.-      I e.45
                                                         BEPA-         16.45

                                                           FROM AEFI t&=2             40
0.:                             k-2   20                 0 EP.R - 20.89
                                                         0 &RR = 18-16
                                                         A EPA=   IS-05

                                4          0’06   O-08    0.10                P



                                                                   -   14.72
                                                         X ERR.=       I I 75

                                                           FROM REF I M-91.75
                                                         m ERR =I5  25
                                                         0 ERR=11   93

                0.02     0.04              0 06   0

          PERFORMANCE       OF LONG   NO2 ZLE                    WI TH
                        COPLANAR    EXIT.
                                                             FIG.               lS(ar   b)

 04 B-

pb          w

  0.1 b-

                                                           0 E P R.=          6.02
 0. 4-
                                                           x E P.R -          3.01


 0 .,2-

                W                               --I-
            0       0   2   0 0                                          7




 0                                                                  -I
                                                           XE.P R.=           2.96
                                                           l REF.        E.P.R=5   0
                                                           l REF         E.P.R=3.0
 0. J


                    0 02     0.04              0 06    ,

      PERFORMANCE    OF LONG NOZZLE                                      WITH
                 COPLANAR   EXIT.
 I *b                                                : 17.96

                                                     =-IS      96

                                                     PR=l4          03






      0                                                             C
                             0.06             0.10

          PERFORMANCE     OF SHORT   NOZZLE          WITH
                   EXTENDED    SHROUD.
                                                                   FIG.   I8



0 09


0 00

0 07


                                                       x k-220
                                                       6 &=a-oI
0 05                                           -

0 04




       0                              I
           0       0 02   0.   4    0.06   0   0              C   ‘0
  PERFORMANCE    OF                SHORT NOZZLE                   WITH
           EXTENDED                 SHROUD.
                                                                                        FIG.         2l.(aeb)



     Of   i -                                                         /


                   --I--                             d,=o~Be

                                                                                         x EPR=6
                                                                                         0 E PR.=3

          )-                  I
               0            0 02       O(                           0 06           0.

P,                                                       0
                   *                        x



                                                                                        x   ~1?1?=5.06
                                                    t&=0       70                       0   EPR.53     02


                            0 02       0 04                         0 06

     PERFORMANCE     OF                                      SHO ?T NOZZLE                         WITH
              EXTENDED                                        SH 4OUD.
                                                                  FIG.          22 (ad)


  04 I-                                                              EPR=        I 9 50
                                                                   AEPR=I          7.84
                                                                   XEPR=rl         6.00
                                  It&‘2   20                       QEPR=l         3 95

  02 ,-

                                                            I             I                   *
                        2   004                0.06        0 08          0 IO                 P
- ‘b

   08 I-


                                                                    X E.P.R - I4 95
                                                                    0EP.R   =I2  00


         C                                                                                    c
                                                      16   008           0 IO             P

        PERFORMANCE      OF ShORT NOZZLE                                  WITH
             BOAT-TAILED      EXTERIOR,
                                                                FIG.         23 (tub)


              f 0
                                                                 XEPRt7         I2
 04                                                         -    OEPR=3         97

                                  t&-I   09


          0         0 02   0’04               0 06    008             0 IO





                                                        I        OEPR-5.00
                                                                 XE.PRr3        00



              III   0 02
                           0 04
                                  *=o    70

                                          0 06

                                                     0 08         0    IO

PERFORMA ‘JCE OF SHORT    NOZZLE                                       WITH-
                                                                             FIG.        24 (a u b)


- ‘b

                                                                              x EP.R =I9     95
                                                                              0 EPR.El7      95
                                                                              + EPR-16       25
                                                                              A E.P R -14.40





                                                                                 + E.PR-I7     95
                                                                                 0 E.PR.sl5.50
                                                                                 X EPR ~14.02

                                          t&*2       20
                               (&OMETRY          AS IN     FIG   7b)

            --r                       I                I
       C                   I          I                I                 I                          B
                        0.02       004               006               008        0 IO      A

           PERFORMANCE                    OF SHORT                      NOZZLE           WITH
                    BASE                   BLOCKAGE.
                                                                               FIG.   25

       0   CObLANAR    EXIT’(BASIC)                 ’
       X   EXTENDED           SHROUD
       A BASE BLOCKAGE            (AS     FIG 7a)
       Q   BASE       BLOCKAGE        (AS FIG 7b)

 I 6


              I   7


                          0           0        0     .




                                                         --cc     El
            MO. r 2.20
            E P.R.eZO
           0.02                0.04            01 36 ,         0 08    <   0    P
  COMPARISON                   OF         RESULTS               FROM       SHORT
                                                             FIG.   26



5-                                                     7
                               X COPLANAR     EXIT (BASIC)
                               Ei EXTENDED   SHROUD
                               B BOAT- TAILED    EXTERIOR



>-                                                                   C
     0   a   2   0,   4    0   6        O-08          C IO

 COMPARISON           OF RESULTS               FROM        SHORT
                                                                                               FIG.   27

                            FROM   REF.1     I 0 P.R 20
                                   THIN      BASE

0 93


                Q)     SHORT       NOZZLl?     WITH       EXTENDED       SHROUD

                @      SHORT       NOZZLE       (BASIC)

                @      SHORT       NOZZLE       WITH       BOAT-TAILED           SXTtRloA
                0      LONG        NOZZLE       (SASIC)

0.90    /               I               I                   I                1                I           w
            0        0.02            0 04                 0.06            0.08              0.10      P

            COMPARISON                       OF OVERALL                          EFFICIENCIES.
                                                                                               FIG.    28

    I                       ul$.eo      7
I.00 -                      E.PRa3       0

                                                                             m FROM    REF 1     DPR   20
                                                                               THIN    BASE
0.90    -

0.70    -

                        0    SHORT           NOZZLE      WITH    EXTENDED        SHROUD

                        @    SHORT           NOZZLE      (BASIC)

                        0    SHORT           NOZZLE      WITH      BOAT-TAILED        EXTERIOR

                        @    LONG NOZZLE               (BASIC.

0 60 r

0.501               I               I                   I                I                I
        0        0.02        0.04                     0 06            008               0 IO

            COMPARISON                  OF OVERALL                       EFFICIENCIES.
                                                             I I
                                                             I j
                                                             I I

                       I        I        I            I          I
4      ’
      (Y        ,”   0         m         0           0          04
           m3        -         A         6           t,         6

    EXfERVNAL              BOUNDARY          LAYER        VELOCITY


0.f                                                                                        0

0. t   0       EXPERIMENTAL   POINTS       II     3”RIG


       ----                   u
                              _ = ;’            5-0.62
                              U  0

       --------I,                     2”    .g=l3.L52
02                            U   0

                                                          II=      LOCAL   VELOCITY
                                                          U     FREE   STEAM    VELOCITY
                                         FIG. 31

                                         FIG. 32

I A.R.C.        C.P.          No.892                                                                  62l-225.1r533.69l                .18&93:    A.R.C.        C.P.    No.&?                                                                     621-225.1:533.6vl                .1&w:
     Febru~.            l%i                                                                           533.6.013.12                                Febnmy,            1 %lt                                                                       533.6.913.12
     bbei-~~,      J.         B.   and   lIole~~orUW,           (1. T.                                                                            Roberts.         J. B. .aM           GolesworC~,              0.       T.

                               AN EWERIIIEWAL        INVEBTIOATION      OF ‘RIE INFWENC!S                            OF                                                    AN EXPERIK?iTkL      INVFSTIG~TICN       OF TIE INFWZSCE                                    OF
I                                   Bk3E BLEED ON THE Bh%            DR.&i OF VARIDUS                                                                                            B.SE BLED      ON THE BXE       DRM OF VARIOW
,                                         PFUJPEUIM:     KGZLE     CONFICUFKTITICNS                                                                                                  PROPELLING     NOZZLE    O3HFIGUBATICMB

                  Var,ous       prppell,ng             nazle        conflguntfons                nlth       all-Internal            exw3.9lo”                     vap10us       pmpe111nB             nozzle         c0nrlBwcl0~                   alth      nil-l”ca?le1             erpas1on
: were      ccsced        In external            flosi     over     the llnBe           of Nach Number                  0.7 Co 2’2.         1”    nere      cesce,         1” excemn1           rim        over      the rrnge           or      Uach Nwlber               0.7 to 2.2.
1 nrder       CO determine             the effect            or base bleed               i1.e.      the      lnje~tl””          Or low             I” otier         Co detemlne             the     errect         or b8.w         bleed       (I..?.      the       lnj?ctlon        or law
   energy       secondary         air)       on base         preSsWe.              A” ~ovenlll            erflclency’             1s jellned,     energy       sHmdary            air)      on b&Se pressure.                      :a *t~eraii              erriciencp~             ~8 mhd,
i tilch       e”“b.bles     the      effectiveness                of base        bleed,        BS 8 me-“s             of reducl”B         the     Iihlch      enables        the errectweneSs                    or base        bleed.        OS a meals               or lY&cl~            Che
/ base      dma,        Co be asseSSed.                  The results             1”dlcat.e       Chat       with        supenonlc                 base      drag,        Co be assessed.                The results              lndlcote           Chat alth            superso”lc
5 exCen,al          llm     ba.398 bleed            BenWalL”           tends       Co mlse          the level             Or base     presS”=e,   external          rlw,     base      bleed      generally            tend3       Co raise           the level            oi b”se      pressu-e
’ b”t     no lmpmeoent                  I” the oVeZ’“ll              ertlclency             1s ObtaIned.                AC SubSOnIC               WC no lmpmvemenc                     1” the o~epall                erriclency             is obceined.                 4 ~U~SO”IC
   external         speeds,       the saandary                 air    h”s       a “eBllBlble            errect          0” bxse                   external          8pee18,       the seamday                  air     has ” “PBllBlble                  efrecf          On ~a.56
   p2SSUre.                                                                                                                                       pl-esure.

t-                                                                                                                                                -~..--                                   __---_                     ------___-_                        .--      -     _-       .___       __

                                                                                                                                                   A.R.C.       C.P.     No&C?                                                                    621-225.1:533.G9.18.aj3:
                                                                                                                                                   FebNWY.            1964                                                                        533.6.013.12
                                                                                                                                                   Robelts.         J. 8.       and    GalesnorChy.              0.      T.
                                                                                                                                                                             AN EXPERIHEtiT&        INKSTIG,‘TION   OF THE INFLUENCF                                   OF
                                                                                                                                                                                     BMSE BIBD         CN TIE LLSE DRAG OF VARIOUS
                                                                                                                                                                                           PROPELLING      NOZZLE COtiFICURATITpJs

                                                                                                                                                                   V,ai-loup      pmpelllng             nozzle         confleuraClans              wlth       all-lntemnl              expansion
                                                                                                                                                   wre       ce~ted         in external           rlow       over      the rylge         or t&h          Nlrmber         0.7 CO 2’2,
                                                                                                                                                    In order         Co ?etemlne              the     errect         or bpse        bleed       (Le.        the      lnjectlo”        or lorr
                                                                                                                                                   energy        secondary         all-1      on base          pressure.            h     ‘0~ei-a          efrichcyr                IS der~ned
                                                                                                                                                   which       enables        the     eriectlveness                of base        bleed,        zs 8 mea”3             Of red”M”B          Chha
                                                                                                                                                   base      drag,        Co be ~a%WSsed.                 lhe results              1”dlcaCe         Chzt      with       su~ersonlc
                                                                                                                                                   external          llm      baSe bleed            generally            tend.3     Co IXlS.2        the      level        Or bzsse pZX%We
                                                                                                                                                   but no lmpmv’aent                     1” the        memll           elrlclency           1s obtnlned.                 ht sUbSO”lC
                                                                                                                                                   external          SpWd3,        the secondary                 nlr     has a “egllglble                MreCC           0” base

                                             C.P. No. 892

        0   Crown     copyrght    1966
       Prmted and pubhshed by
          To be purchased from
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        or through any bookseller

            Printed   m England

                                             C.P. No. 892
                                             S.O. Code No   23-9016-92