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incorrect Strouhal number with RANS in high Re number |
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#1 |
Member
Amir
Join Date: Jan 2017
Posts: 32
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Hello,
I have a problem with simulation of a flow around a cylinder in high Re number. I tried to read all related posts and threads, but it doesn't solve my problem. so I need your help to get rid of it. It is a 2D case with a cylinder (D=54 cm) in the middle. I am modelling it with the komegaSST model. the Strouhal number from my simulation is always 0.17, however, it should be around 0.13. the Re number is 2e5, and I am not sure that the komegaSST is able to solve it properly! I am going to provide as much detail as I can here to be sure that my solution is correct. I will appreciate if somebody gives me feedback. U Code:
/ internalField uniform (0.3 0 0); boundaryField { INLET { type fixedValue; value uniform (0.3 0 0); } SIDES { type symmetry; } CYLINDER { type fixedValue; value uniform (0 0 0); } OUTLET { type zeroGradient; } UPODOWN { type empty; } } Code:
internalField uniform 0; boundaryField { INLET { type zeroGradient; } SIDES { type symmetry; } CYLINDER { type zeroGradient; } OUTLET { type fixedValue; value uniform 0; } UPODOWN { type empty; } } Code:
internalField uniform 0.07; boundaryField { INLET { type turbulentMixingLengthFrequencyInlet; mixingLength 0.54; phi phi; k k; value uniform 1; } SIDES { type symmetry; } CYLINDER { type omegaWallFunction; value uniform 0.07; } OUTLET { type inletOutlet; inletValue uniform 0.07; value uniform 0.07; } UPODOWN { type empty; } } Code:
internalField uniform 0.1; boundaryField { INLET { type calculated; value uniform 0; } SIDES { type symmetry; } CYLINDER { type nutUWallFunction; value uniform 0.1; } OUTLET { type calculated; value uniform 0; } UPODOWN { type empty; } } Code:
internalField uniform 0.000398; boundaryField { INLET { type turbulentIntensityKineticEnergyInlet; intensity 0.05; value uniform 0.000398; } SIDES { type symmetry; } CYLINDER { type kqRWallFunction; value uniform 0.000398; } OUTLET { type inletOutlet; inletValue uniform 0.000398; value uniform 0.000398; } UPODOWN { type empty; } } Code:
application pimpleFoam; startFrom startTime; startTime 0; stopAt endTime; endTime 500; deltaT 0.001; writeControl adjustableRunTime; writeInterval 50; purgeWrite 0; writeFormat ascii; writePrecision 6; writeCompression uncompressed; timeFormat general; timePrecision 6; runTimeModifiable yes; adjustTimeStep yes; maxCo 0.5; Code:
ddtSchemes { default backward; } gradSchemes { default leastSquares; // grad(U) cellLimited Gauss linear 1; } divSchemes { div(phi,U) Gauss linearUpwindV Gauss linear; div(phi,k) Gauss linearUpwind Gauss linear; div(phi,omega) Gauss linearUpwind Gauss linear; div((nuEff*dev(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear corrected; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } fluxRequired { default no; p ; } Code:
solvers { p { solver GAMG; tolerance 1e-6; relTol 0.001; smoother GaussSeidel; nPreSweeps 0; nPostSweeps 2; cacheAgglomeration on; agglomerator faceAreaPair; nCellsInCoarsestLevel 10; mergeLevels 1; } pFinal { $p; relTol 0; } "U|k|omega" { solver PBiCG; preconditioner DILU; tolerance 1e-06; relTol 0.001; } "(U|k|omega)Final" { $U; tolerance 1e-05; relTol 0; } } PIMPLE { nOuterCorrectors 1; nCorrectors 2; nNonOrthogonalCorrectors 2; } Regards, Amir |
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#3 |
Member
Amir
Join Date: Jan 2017
Posts: 32
Rep Power: 9 ![]() |
Dear Tobi,
Many thanks for your reply. I calculate the Strouhal number by measuring the Cl on the cylinder and by following the time period of each full sinusoidal move in the graph or using the fast Fourier transform method. I attached here the results of my Cl here. Regards, Amir |
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#4 |
Super Moderator
Tobias Holzmann
Join Date: Oct 2010
Location: Bad Wörishofen
Posts: 2,711
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I agree that the estimation of the function is correct. However, Re = 200.000, is high turbulent and your statement does not fit to the physical behavior of the Strouhal Number and my reference [1]. Here, the following is stated:
Summing up. You are saying that you should get a Sr number of around 0.13. However, that would imply that you should have a Re number of around 80. This would agrees well to my studies that I made a few years ago. And if that is the case, you are laminar and no turbulence model is needed. I attached a figure of my previous work. You can see that c_d is arount 0.9x and the Reynolds number was 300. KaramanCd.jpg [1] H.Schlichting, K.Gersten: Grenzschichttheorie, Springer–Verlag Berlin Heidelberg (2007)
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Keep foaming, Tobias Holzmann |
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#5 |
Member
Amir
Join Date: Jan 2017
Posts: 32
Rep Power: 9 ![]() |
Dear Tobi,
I made a mistake in my statement, the values I mentioned was for the frequency of the vortex shedding for my case from the Sr number. the frequency of vortex shedding for Sr=0.21 for my case should be around 0.13, but from simulation, the frequency is around 0.17 which is equivalent to Sr =0.28. I am sorry for the mistake. Regards, Amir |
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#6 |
Senior Member
Peter Baskovich
Join Date: Jul 2014
Posts: 127
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How close are your boundaries to the sphere?
Have you done a mesh dependancy study? |
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#7 |
Member
Amir
Join Date: Jan 2017
Posts: 32
Rep Power: 9 ![]() |
Dear Peter,
Many thanks for your reply, to be sure that everything is fine, I tried it with different size of the domain. I have attached one of them. the quality of mesh is very good in case of max angle, and also I checked it with checkMesh and everything is ok. this mesh includes 33000 cells. The only thing that I think can cause a problem is the min yplus around the cylinder. min y+ =1.33 max y+=78.5 average y+=42 since I used the nutUwallFunction! I checked it with nutUSpaldingWallFunction, and got the same results. Kind regards, Amir Last edited by albet; November 3, 2018 at 16:06. |
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