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CFD Workshop on Test Cases, Databases & BPG for Nuclear Power CFD Workshop on Test Cases, Databases & BPG for Nuclear Power Plants Applications, 16 July 2008.Plants Applications, 16 July 2008.

CFD Quality & Trust: mixed and CFD Quality & Trust: mixed and natural convection natural convection

test cases test cases The

Uni

vers

ity

of M

anch

este

r

Yacine AddadSchool of MACE ,

University of Manchester

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The buoyancy-opposed wall jetThe buoyancy-opposed wall jet(QNET-CFD Application challenge TA3 – case 1)(QNET-CFD Application challenge TA3 – case 1)

18 m m

38 m m

Je t In flo wm = 3 .0 3 k g /sje t

U p w ard C h an n e l f lo wm = 3 .8 8 k g /sC

O u tflo w

Y

X

Z

•Non-buoyant case

•buoyant case low aspect Velocity ratio

•buoyant case high aspect Velocity ratio

3

ExpStar – SmagoSaturne DynSaturne fine mesh

Vertical (V)&

Horizontalmean velocity

profiles

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Thermal hydraulics of reactorsThermal 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 studyCoaxial 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).

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CASE-4: Ra=2.3810E+10

CASE-3: Ra=2.3810E+10

Natural Convection in coaxial cylindersNatural Convection in coaxial cylinders

Case 2: Ra=1.810E+9SGS visc/Molecular visc.<1

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Coaxial Cylinder – effect of PrCoaxial Cylinder – effect of Prtt and convection scheme and convection scheme

Mean Temperature

Y. Addad with Star-CD

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Rms temperature fluctuationsPrt = 0.9 + bounded convection scheme is OK

Prt = 0.4 + CDS

Coaxial Cylinder – effect of PrCoaxial Cylinder – effect of Prtt and and convection schemeconvection scheme

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3 Cylinders test case3 Cylinders test case

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NEARLY-HORIZONTAL SHALLOW CAVITYNEARLY-HORIZONTAL SHALLOW CAVITY TEST CASETEST CASE

• Ra= 4.16108 • NCELL= 3 million• Boussinesq approximation• Pr=0.71 (Air)• =5°

LES Grid (Case1)

0.8h

Plan Y-Z

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NEARLY-HORIZONTAL SHALLOW CAVITYNEARLY-HORIZONTAL SHALLOW CAVITY TEST CASETEST CASE

LES RESULTS

Q=0.05

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• Ra= 4.16108 • NCELL= 3 million (same grid)• Boussinesq approximation• Pr=0.71 (Air)• =15°

LES Grid (Case2)

NEARLY-HORIZONTAL SHALLOW CAVITYNEARLY-HORIZONTAL SHALLOW CAVITY TEST CASE TEST CASEIn progress

Q=0.05 (same value as Case1)

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V gradient away from wall=> Turbulence increase

V gradient nearer wall=> Turbulence decrease

buoyancy aidingbuoyancy aiding

buoyancy opposingbuoyancy opposing

Buoyancy aiding or opposing vertical pipe flowBuoyancy aiding or opposing vertical pipe flow

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0.3

0.5

0.7

0.9

1.1

1.3

1.5

0.01 0.1 1 10

Bo

Nu

/Nu

0

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)

Buoyancy opposing vertical pipe flow RANS predictionsBuoyancy opposing vertical pipe flow RANS predictions

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Conclusions and future workConclusions 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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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.

List of PublicationsList of Publications