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
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,  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,  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  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  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  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.  The negatively buoyant wall-jet: LES database Int. J. Heat fluid Flow 25, pp795-808. 16
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