of Manchester The University CFD Workshop on Test Cases, Databases & BPG for Nuclear Power Plants Applications, 16 July 2008. CFD Quality & Trust: mixed and natural convection test cases Yacine Addad School of MACE , University of Manchester

1 The buoyancy-opposed wall jet (QNET-CFD Application challenge TA3 case 1) Non-buoyant case O u tflo w J e t In flo w m je t= 3 . 0 3 k g / s 18 m m 38 m m buoyant case low aspect Velocity ratio

buoyant case high aspect Velocity ratio Y X Z U p w a rd C h a n n e l flo w m C= 3 .8 8 k g /s 2 Exp Star Smago Saturne Dyn

Saturne fine mesh Vertical (V) & Horizontal mean velocity profiles 3 Thermal hydraulics of reactors Mixed convection in co-axial pipe (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 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=1.8109) Exp. Ref. McLeod 89 Case3- annular cavity single coaxial cylinder (Ra=2.381010) Case4- annular cavity with 3 coaxial cylinders (Ra=2.381010) Case5- Flow in a horizontal penetration (bulk Re=620,000). 5 Natural Convection in coaxial cylinders CASE-3: Ra=2.3810E+10 Case 2: Ra=1.810E+9 SGS visc/Molecular visc.<1 CASE-4:

Ra=2.3810E+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= 4.16108 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= 4.16108 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 aiding buoyancy opposing V gradient away from wall => Turbulence increase 13 Buoyancy opposing vertical pipe flow RANS predictions 1.5 1.3 Nu/Nu 0

1.1 Launder & Sharma Model (CONVERT) Cotton & Ismael Model (CONVERT) Suga Non-Linear Eddy Viscosity Model (CONVERT) Lien-Chen-Leschziner k-eps Model (STAR-CD) k-omega-SST Model (STAR-CD) Lien & Durbin v2f Model (STAR-CD) k-omega-SST Model (Code_Saturne) Manchester v2f Model (Code_Saturne) Large Eddy Simulation (STAR-CD) DNS - You et al (2003) 0.9

0.7 0.5 0.3 0.01 0.1 1 Bo 10

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 presimulation 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