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

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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

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

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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)

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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 10 10 ) Case4- annular cavity with 3 coaxial cylinders (Ra=2.38 10 10 ) Case5- Flow in a horizontal penetration (bulk Re=620,000).

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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

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

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8 Rms temperature fluctuations Prt = 0.9 + bounded convection scheme is OK Prt = 0.4 + CDS Coaxial Cylinder – effect of Pr t and convection scheme

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9 3 Cylinders test case

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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

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

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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)

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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

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14 Buoyancy opposing vertical pipe flow RANS predictions

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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).

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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, pp795-808. List of Publications

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