NAFEMS Awareness Seminar � Conventry March 2004

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NAFEMS Awareness Seminar � Conventry March 2004 Powered By Docstoc
					                   CFD Workshop on Test Cases, Databases & BPG for Nuclear Power
                   Plants Applications, 16 July 2008.
The University
of Manchester


                 CFD Quality & Trust: mixed and
                      natural convection                             O u tflo w
                                                                     r e g io n

                                                                                  y
                                                                                          Jet



                                                                                                x




                                                                       C o ld u p flo w




                          test cases




                                               Yacine Addad
                                             School of MACE ,
                                          University of Manchester
                                                                                                    1
       The buoyancy-opposed wall jet
      (QNET-CFD Application challenge TA3 – case 1)
  Outflow                           •Non-buoyant case
                  Jet Inflow
                  mjet=3.03 kg/s


                      18 mm

                      38 mm        •buoyant case low aspect Velocity ratio




                                   •buoyant case high aspect Velocity ratio
    Y


            X
  Z


Upward Channel flow                                                 2
   mC=3.88 kg/s
   Exp
   Star – Smago
   Saturne Dyn
   Saturne
   fine mesh




 Vertical (V)
      &
 Horizontal
mean velocity
  profiles




       3
                          Thermal hydraulics of reactors

                                      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
University of Manchester by
Gerasimov et al.                                                        4
                 Coaxial heated cylinder study




• 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) Exp. Ref. McLeod 89
   Case3- annular cavity single coaxial cylinder (Ra=2.381010)
   Case4- annular cavity with 3 coaxial cylinders (Ra=2.381010)
   Case5- Flow in a horizontal penetration (bulk Re=620,000).

                                                                          5
                       Natural Convection in coaxial cylinders

         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




                                                                    6
Coaxial Cylinder – effect of Prt and convection scheme




                                 Mean Temperature



                  Y. Addad with Star-CD
                                                    7
Coaxial Cylinder – effect of Prt and convection scheme




                            Rms temperature fluctuations
                       Prt = 0.9 + bounded convection scheme is OK
                                      Prt = 0.4 + CDS
                                                           8
3 Cylinders test case




                        9
            NEARLY-HORIZONTAL SHALLOW CAVITY TEST CASE


 LES Grid (Case1)

• Ra= 4.16108
• NCELL= 3 million
• Boussinesq approximation
• Pr=0.71 (Air)
• =5°
                                       Plan Y-Z




                                         0.8h     10
              NEARLY-HORIZONTAL SHALLOW CAVITY TEST CASE

LES RESULTS




   Q=0.05




                                                     11
             NEARLY-HORIZONTAL SHALLOW CAVITY TEST CASE
                                  In progress

   LES Grid (Case2)

 • Ra= 4.16108
 • NCELL= 3 million (same grid)
 • Boussinesq approximation
 • Pr=0.71 (Air)
 • =15°




Q=0.05 (same value as Case1)




                                                    12
       Buoyancy aiding or opposing vertical pipe flow


V gradient nearer wall
=> Turbulence decrease          buoyancy opposing




 buoyancy aiding               V gradient away from wall
                               => Turbulence increase

                                                           13
                      Buoyancy opposing vertical pipe flow RANS predictions
          1.5
                    Launder & Sharma Model (CONVERT)
                    Cotton & Ismael Model (CONVERT)
                    Suga Non-Linear Eddy Viscosity Model (CONVERT)
                    Lien-Chen-Leschziner k-eps Model (STAR-CD)
          1.3
                    k-omega-SST Model (STAR-CD)
                    Lien & Durbin v2f Model (STAR-CD)
                    k-omega-SST Model (Code_Saturne)
                    Manchester v2f Model (Code_Saturne)
          1.1       Large Eddy Simulation (STAR-CD)
                    DNS - You et al (2003)
Nu/Nu 0




          0.9



          0.7



          0.5



          0.3
             0.01                    0.1                             1        10
                                                    Bo                   14
                 Conclusions and future work
LES of Industrial flow
   • Complex geometry LES easier than smooth channel flow
   • Responds to Industry needs:
                 Thermal stresses, fatigue, Acoustics, FIV (vibrations)
    • Cost-wise accessible when limited to sub-domain
                  (next step RANS-Embedded LES )
• Unstructured griding with professional software:
    • Flexibility
    • Possible Quasi-DNS near wall resolution at Medium Re numbers
    • 2nd order accuracy may be sufficient.
• Further developments and validation needed:
    • More griding flexibility (total cell size control from pre-simulation
    RANS and/or coarse LES).
    • Further testing of Polyhedral cells for LES (advantage: Energy
    conservation).
    • Run a benchmark computations to compare LES predictions with
    different codes (in-house via commercial).


                                                                          15
                                List of Publications

A. Keshmiri, M.A. Cotton, Y. Addad, S. Rolfo, and F. Billard, [2008] “RANS and LES
Investigations of Vertical Flows in the Fuel Passages of Gas-Cooled Nuclear Reactors”, 16th Int.
Conf. on Nuclear Engineering, ‘ICONE16’.

A. Keshmiri, M.A. Cotton, Y. Addad, D.R. Laurence, and F. Billard, [2008] “Refined Eddy
Viscosity Schemes and LES for Ascending Mixed Convection Flows”, Proc. 4th Int. Symp. on
Advances in Computational Heat Transfer ‘CHT-08’.

Y. Addad, M. Mahmoodilari, and D. Laurence [2008] “LES and RANS Computations of Natural
Convection in a Nearly-Horizontal Cavity” Proc. 4th Int. Symp. on Advances in Computational
Heat Transfer, ‘CHT-08’.

Y. Addad, D. R. Laurence [2008] “LES for Buoyancy-Modified Ascending Turbulent Pipe
Flow”, 7th International ERCOFTAC Symposium on Engineering Turbulence Modelling and
Measurements (ETMM7) .

Y. Addad, D. Laurence, and M. Rabbitt [2006] “Turbulent Natural Convection in Horizontal
Coaxial Cylindrical Enclosures: LES and RANS Models” Turbulence, Heat and Mass Transfer 5.

Addad Y., Benhamadouche S., and Laurence D. [2004] “The negatively buoyant wall-jet: LES
database” Int. J. Heat fluid Flow 25, pp795-808.
                                                                                    16

				
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