Docstoc

NAFEMS Awareness Seminar – Conventry March 2004

Document Sample
NAFEMS Awareness Seminar – Conventry March 2004 Powered By Docstoc
					                                                                              EDF
The University   Materials Performance Centre Seminars, 12/09/2006            Electricité
                                                                              de France
of Manchester


                     Application of Large Eddy Simulation
                             to thermal-hydraulics
                  in the Nuclear Power Generation Industry.


                         Dominique.Laurence@manchester.ac.uk
                             School of Mech, Aero & Civil Eng.
                                 Fluids AIG / CFD group
                              Dominique.Laurence@edf.fr
                                    EDF R&D Chatou



Contributions:
Y. Addad, I. Afgan, S. Benhamadouche, S. Berrouk, N Jarrin C. Moulinec, T. Pasutto,



                                                                          1
                                                               EDF
               Turbulence, Reynold Number Re = UD/visc.        Electricité
                                                               de France



                                         Low speed jet




Osborne Reynolds
 1868, became a professor of
engineering at Owens College
(now University of Manchester)

                                        Higher speed jet




   Reynolds tank, G. Begg building
                                                           2
                                                                          EDF
                  Kolmogorov Energy Cascade                               Electricité
                                                                          de France




 Андре́й Никола́евич
    Колмого́ров
Moscow State Uni. 1939


          Assume :       u( x )  ui sin(ki x )   ki  2 / Li
            du
          u.  ui 2ki sin(ki x ) cos(ki x )  12 ui 2ki sin(2ki x )
            dx
          thus energy transfer from ki  2 / Li to 2ki  2 /( 12 Li )
                                                                    3
                                                                                          EDF
                Direct Numerical Simulation (DNS)                                         Electricité
                                                                                          de France




Solve the standard (Navier Stokes) flow equation on a very fine mesh
- All scales are resolved on that mesh (down to Kolmogorov scale)
- No model needed
- Results considered as valid as experimental data
- Enormous computer resources, for even modest speed-domain size (Reynolds number)




                                                 Nx=6144, Ny=633, Nz=4608 points
                                                        = 17,921,212,416 cells
                                           6 Million processor hours on 2048 processors,
                                                  Barcelona Supercomputing Center
                                    Sergio Hoyas and Javier Jimenez, (2006) "Scaling of
                                    velocity fluctuations in turbulent channels
                                    up to Re_tau = 2000", Phys. of Fluids, vol 18,
                                                                                   4
                                                                      EDF
           Luckily, only Large Scales matter (most of the time)       Electricité
                                                                      de France




 Large Scales & Human activity
   • Drag, mixing, heat transfer,
   • Large Scales dictate flow physics
   • Generated by/scale with obstacle
   • Impose dissipation rate
 Exceptions: noise, combustion,
Weather forecast (we are the small scales !)




                                                                  5
                                                                   EDF
                           Large Eddy Simulation = Filtering       Electricité
                                                                   de France



Time Filter
                   t T                   1
 u( x, t )            u( x, t  t ')    dt '
                t T                     2T
Space Filter

  u ( x, t )   u (r , t )G( x  r )dr
                    V




           CFD codes naturally
       induce filter D = 2 dx
                                                               6
                                                          EDF
                DHIT: Decay of Hom. Iso. Turb.            Electricité
                                                          de France




MANDATORY test case for first time LES !
Reveals numerical dissipation, stability,
                          Grid



            U0=10 m s-1
                                 Station    Station
                                   42         98




                                                      7
            3 Levels of CFD approaches to turbulent flow                     EDF
                                                                             Electricité
                                                                             de France




• Direct Numerical Simulation (DNS) databases <=> Experiments
          = “Costly” Fluid Dyn., exceptional, limited to zoom effect,
          - 100% accurate, back to 1st principles, NO modelling hypothesis

• Large Eddy Simulation (LES)
         = “Colourful” Fluid Dyn., much detail, fluctuations, spectra,
         - Applicable Eng. problems, at some cost
         - Almost as reliable as DNS, but know-how required, not well established

• Reynolds Averaged (RANS)
        = “Conventional” Fluid Dyn., used daily in Eng., only mean values (B&W)
        - Economical, full reactor or sub-component design (parametric) possible
        - Problem: wide range of models to choose from,
        - needs improvement & validation for new range of applications
        (high temperature, buoyancy, conjugate heat transfer, )

    Future : Coupling of RANS and LES, using DNS for insight & validation


                                                                        8
                 Industrial LES applications                              EDF
                                                                          Electricité
                 to reactor thermal hydraulics                            de France



                    LES is mostly about numerical methods
Grid able to capture most turbulent scales
     Easier in Power Industry (confined, non-streamlined geometry)
     Local/embedded grid refinement, polyhedral scales
Boundary conditions
     Walls => quasi DNS (wall functions not ideal)
     Some real periodic geometry. pb. in Power Gen (tube bundles)
     Synthetic inlet turbulence
Target values
     Order of Mag. (within 10%), not 0.01 on Cd
     Thermal mixing & loading, spectra, vibrations….
Need Fast Unstructured FV Solver
        EDF code Saturne & Star-CD very similar
High Accuracy Numerical Scheme
     No numerical dissipation
     ( Central differencing, Second order in time)
     Avoid any mesh distortion
                                                                      9
                                                                                EDF
              LES at EDF: Thermal stresses in T junction                        Electricité
                                                                                de France



      - Experimental mock-up
      (both thermalhydraulics and thermal fatigue mechanical aspects)
      - models and numerical tools to gain a better understanding.




                                                                Qhot
                                                                                Qcold

Configuration studied :
Thot = 168°C , Tcold = 41°C                 Length of the numerical simulation :
Flow rate = 1000 m3/h, ratio 20%            11 seconds

                                                                           10
                                                               EDF
Fluid results                                                  Electricité
                                                               de France




  Instantaneous fluid temperature field
  (Code_Saturne)

      (Peniguel et al. ASME-PVP Cleveland 2003)
                         Shortcut to aaPVP_anim.mpg.lnk   11
                                                                              EDF
              Solid and fluid meshes                                          Electricité
                                                                              de France




Solid mesh : 958 975 nodes                       Fluid mesh: 401 472 cells
width of the first solid element : 100 microns


                                                                         12
                                                 EDF
         Solid temperature fluctuations          Electricité
                                                 de France




Instantaneous solid temperature field
(Syrthes)
(location C12)
                                                 C12


        Instantaneous fluid temperature
          Instantaneous solid temperature




                      Time (s)

                                            13
Temperature spectrum
                                              EDF
                                              Electricité
                                              de France




                             - On site meas
     CEX1                    -L.E.S.
                             - Mock-up




            Frequency (Hz)




            Location CEX1
                                       14
                                                                       EDF
                       T Junction, stratified case                     Electricité
                                                                       de France




  Fluid temperature and
  flow structure
                                             VH = 3,37 m/s
                                             TH = 204°C



         VC = 0,77 m/s
         TC = 41°C
Temperature In the symmetry plane (case 1)




                                                      C12

   Temperature near the wall (case 1)                             15
                                             Recirculation zone
                                                                      EDF
                  Analysis of the results                             Electricité
                                                                      de France




Attenuation of the fluctuations by
the wall thermal inertia




                                            ( Ring C12 – 50 °)




                                                                 17
                                                                                                   EDF
                   Mesh too coarse for Re=1 Million                                                Electricité
                                                                                                   de France



 temperatures (ring C12)
  fluid:          probe located at 10°                       probe located at 50°




  Solid:
                                                                               Exp



                                                                          LES



 underestimation of the fluctations (especially at 10°)  limitation of the wall function approach ?
                                                                                               18
             FAATER exp. : Meshes                                                EDF
                                                                                 Electricité
                                                                                 de France



Fluid meshes
 1st mesh : ~ 500 000 hexaedric cells  y+~ 300
 2nd mesh : ~ 1 000 000 hexaedric cells  y+~ 170 (first node at 0,38 mm from
the wall)




                                                               (1 000 000 cell
                                                               mesh)




                                                                          19
                    Trust & Quality-CFD project: hot wall jet                                           EDF
                                                                                                        Electricité
                    (Magnox case)                                                                       de France




             O u t f l o w
              r e g i o n
                                  Jet
                        y


                                         x




               C o ld u p flo w



                     Buoyancy:                             none
     3-D view (STCL2). A: t 1 =2114 D j /V bj Ý , B: t t 2 =t 1 + 5D j /V bj Ý .
                                              sÞ                 18.         sÞ
                                                                                   medium   high
                     Velocity:                              high                   medium    low
Addad Y. , D. Laurence and S. Benhamadouche.
The Negative Buoyant Wall Jet: LES Results, I.J. Heat and Fluid Flow, 25, 795-808, 2004
                                                                                                   20
                                                             EDF
                  Grid generation (buoyant case)             Electricité
                                                             de France




●   Pre- k-eps simulation                          Integral
                                                   Length scale
                                                   from k-epsilon
● cell Volume near jet
inlet (V)1/3=0.002
● y+=1




●In mixing region
(V)1/3=0.007

●   NCELLS=770 000

StarCD code
●




                                                        22
                                      EDF
Horizontal Velocity Comparison        Electricité
                                      de France




                                 23
                                               EDF
LES DB => Analytic Wall Function development   Electricité
                                               de France




         (from A. Gerasimov)              24
                                                                            EDF
                          Thermal hydraulics of reactors                    Electricité
                                                                            de France




                                      Mixed convection in co-axial pipes
                                        (Y. Addad PhD, M. Rabitt British Energy)




Study the physics of the flow in
the decay heat inlet pen

Examine the LES solution of the
code Star-CD for the
natural/mixed convection cases.

Validate further the analytical
wall functions developed at
UMIST by Gerasimov et al.
                                                                       25
Cold Inlet Pipe in vessel => stratification trap        EDF
                                                        Electricité
                                                        de France




        Streamlines coloured by temperature



                                              K-eps
                                              pre-study




                                                   26
                                                                        EDF
                Coaxial heated cylinder study                           Electricité
                                                                        de France



• LES validation and parametric test cases:
   Case1-Natural convection in square cavity (Ra=1.58  109)
   Case2-Natural convection in annular cavity (Ra=1.8109)
   Case3- annular cavity single coaxial cylinder (Ra=2.381010)
   Case4- annular cavity with 3 coaxial cylinders (Ra=2.381010)
   Case5- Flow in actual penetration cavity (bulk Re=620,000).




                                                       Bishop 88, McLeod 89

                                                                   27
                                                                   EDF
                       Natural Convection in coaxial cylinders     Electricité
                                                                   de France




         CASE-3: Ra=2.3810E+10




 Case 2: Ra=1.810E+9
SGS visc/Molecular visc.<1
                                                  CASE-4: Ra=2.3810E+10




                                                              28
3 Cylinders        EDF
                   Electricité
                   de France




              30
                                                                      EDF
                     Flow through in-line tube bundles                Electricité
                                                                      de France



 Objectives: Flow induced vibrations
in heat exchangers (Lift & Drag coef.)
 Staggered: studied 10 years ago
         Current: in line




      Large heat exchanger
   => Homogeneous conditions
   => Periodic subset considered

   Re=45 000, P/D= 1.5

                                                         STAR CCM grid
                                                                 31
                                                                                   EDF
                    In-line tube bundle                                            Electricité
                                                                                   de France




- Fully symmetric conditions,
but non-symmetric solutions

- Coanda effect ?

- Star-CCM LES launched
to confirm EDF finding
(Benhamadouche et al. NURETH
11, Avignon 2005)




     Time averaged
     velocity field =>




                                I.Afgan@postgrad.manchester.ac.uk, with STAR-CCM
                                                                              32
                                                                                                                            EDF
            In-line tube bundle P/D=1.5                                                                                 Electricité
                                                                                                                        de France
                                                                               Normalized Pressure Distributions

                                                      1.00
                                                                                                                      SATURNE
                                                                                                                      STAR CCM
                                                      0.75

                                                      0.50




                                Normalized Pressure
                                                      0.25

                                                      0.00

                                                      -0.25

                                                      -0.50

                                                      -0.75
                                                                                                              Azimuthal Angle

                mean pressure
                                                      -1.00
                                                              0      45   90      135      180     225     270        315       360




 STAR CCM                                                         EDF Code-Saturne
Mean velocity                                                       Mean velocity
  (Afgan)                                                         (Benhamadouche)




                                                                                                                 33
                     LES in a 180° U-Bend Pipe        EDF
                                                      Electricité
                                                      de France




-Vortex Method for Inlet
-Polyhedral Cells (670,000)
-Re=57,400
-Y+=2 (Prisms)
-L1=3D; L2=5D
- Smagorinsky Model, Van Driest
   Damping                                       34
                                                      EDF
         U-Bend Pipe Cross Sections: Mean flow        Electricité
                                                      de France




                         135 degrees




177 degrees




                              45 degrees



   90 degrees                                    36
                                                     EDF
Research: Reconstructing fluctuations                Electricité
                                                     de France




                            Real Eddies in Channel flow
                             Cost = 5 days computing




                           Synthetic Eddies in Channel flow
                             Cost = 5 seconds computing

                              Matches all rms values and
                                   given spectrum



                             KNOO project:
                      Develop similar technique to
                       reconstruct temperature
                        fluctuations at solid wall


                      Link with materials ageing research


                                                37
                                                                                                      EDF
                   Research: Mesh strategy for LES                                                    Electricité
                                                                                                      de France




a)




     Possible FV near-wall refinements: a) dichotomy, b) non-conforming, c) & d) polyhedral & zoom.

        - Non dissipative Finite Volume Methods

        - Optimal meshing strategy for LES

        - Quality criteria for LES
                  General but essential issue. Collaboration with:
                  - CD – Adapaco (STAR-CD code)
                  - EDF R&D (Saturne code)
                  - Health & Safety Labs, CFD for Nuclear Reactor licensing ?


                                                                                             38
       Research: RANS – LES coupling
                                                                       EDF
                                                                       Electricité
                                                                       de France



DNS at Re*    N Cells

395           10 Million             U
640           28 Million
720           84 Million
2000          17,921 Million
                    RANS – LES coupling   Under-resolved LES

                                                       Wall distance
             RANS       LES

                                           LES: ~ 0.1 Million cells

                                              J. Uribe, Manchester




                                                                 39
                Conclusions – Industrial LES                                  EDF
                                                                              Electricité
                                                                              de France



• LES of Industrial flow
    • Much more information:
                Thermal stresses, fatigue, Acoustics, FIV (vibrations)
    • Cost-wise accessible when limited to subdomain
                (synthetic turbulence for inlet)
    • Complex geometry possibly easier than smooth channel flow
                                          (academic overkill ?)

• Flexible flexibility with professional/commercial software:
     • Opens new range of applications for LES
     • Medium Re number : DNS near wall resolution possible
     • Greater breakthrough than elaborate SGS models?

• Further developments:
    • More meshing control (total cell size control from pre-simulation)
    • High Re : RANS –LES coupling, embedded LES

• Cross-discipline research: Fluids / Structure-Mech/ Materials ?
                         Cracks, Thermal stripping, ageing, corrosion …
                                                                         40

				
DOCUMENT INFO