1 CFD Workshop on Test Cases, Databases & BPG for Nuclear Power Plants Applications, 16 July CFD Quality & Trust: mixed and natural convection test cases The University of Manchester Yacine Addad School of MACE, University of Manchester

2 The buoyancy-opposed wall jet (QNET-CFD Application challenge TA3 – case 1) Non-buoyant case buoyant case low aspect Velocity ratio buoyant case high aspect Velocity ratio

3 Exp Star – Smago Saturne Dyn Saturne fine mesh Vertical (V) & Horizontal mean velocity profiles

4 Thermal hydraulics of reactors 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. Mixed convection in co-axial pipes (Y. Addad PhD, M. Rabitt British Energy)

5 Coaxial heated cylinder study LES validation and parametric test cases: Case1-Natural convection in square cavity (Ra=1.58  10 9 ) Case2-Natural convection in annular cavity (Ra=1.8  10 9 ) Exp. Ref. McLeod 89 Case3- annular cavity single coaxial cylinder (Ra=2.38  ) Case4- annular cavity with 3 coaxial cylinders (Ra=2.38  ) Case5- Flow in a horizontal penetration (bulk Re=620,000).

6 CASE-4: Ra=2.38  10E+10 CASE-3: Ra=2.38  10E+10 Natural Convection in coaxial cylinders Case 2: Ra=1.8  10E+9 SGS visc/Molecular visc.<1

7 Coaxial Cylinder – effect of Pr t and convection scheme Mean Temperature Y. Addad with Star-CD

8 Rms temperature fluctuations Prt = bounded convection scheme is OK Prt = CDS Coaxial Cylinder – effect of Pr t and convection scheme

9 3 Cylinders test case

10 NEARLY-HORIZONTAL SHALLOW CAVITY TEST CASE Ra= 4.16  10 8 NCELL= 3 million Boussinesq approximation Pr=0.71 (Air)  =5° LES Grid (Case1) 0.8h Plan Y-Z

11 NEARLY-HORIZONTAL SHALLOW CAVITY TEST CASE LES RESULTS Q=0.05

12 Ra= 4.16  10 8 NCELL= 3 million (same grid) Boussinesq approximation Pr=0.71 (Air)  =15° LES Grid (Case2) NEARLY-HORIZONTAL SHALLOW CAVITY TEST CASE In progress Q=0.05 (same value as Case1)

13 V gradient away from wall => Turbulence increase V gradient nearer wall => Turbulence decrease buoyancy aiding buoyancy opposing Buoyancy aiding or opposing vertical pipe flow

14 Buoyancy opposing vertical pipe flow RANS predictions

15 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).

16  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”, 16 th 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. 4 th 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. 4 th Int. Symp. on Advances in Computational Heat Transfer, ‘CHT-08’.  Y. Addad, D. R. Laurence [2008] “LES for Buoyancy-Modified Ascending Turbulent Pipe Flow”, 7 th 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, pp List of Publications