# k-Omega SST - Wall functions in OF 2.3

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 November 6, 2015, 07:36 k-Omega SST - Wall functions in OF 2.3 #1 Senior Member     shereez Join Date: Jan 2014 Location: England Posts: 188 Rep Power: 4 I have read a lot of posts in this forum regarding Wall Functions in OF. But could not arrive at an answer that satisfies me. I have a mesh for Naca 0012 airfoil with Y+ ~= 1 My understanding up to now: 1) Without Wall function - ( wall/airfoil/solidwall) (// Y+ less than or =1) * Omega - Type: omegaWallfunction value: 1e-18; // non zero low value * K Type: KqRWallfunction value: 1e-18 ; // non zero low value * nut Type : nutkWallfunction value: uniform 0; 2) With Wall function - ( wall/airfoil/solidwall) (Y+ 30 to 100) * Omega Type: omegaWallfunction value: 300; // some value from formulaes or guess * K Type: KqRWallfunction value: 0.1 ; // some value * nut Type: KqRWallfunction value: uniform 0; Is this correct? Or what is the actual implementation: I intend to use without wall functions. Some other information that might be useful: * Re = 2 million * Mach = incompressible * K = turbulentKineticEnergyinlet with intensity specified * High Angle of Attack region. * FV schemes: (divergence of U) * bounded Gauss limitedLinearV 1; (divergence of k|Omega) *bounded Gauss limitedLinear 1; * Time Integration: Euler please input your views. Any input is appreciated very much

 November 6, 2015, 16:14 #2 Senior Member   Joachim Herb Join Date: Sep 2010 Posts: 387 Rep Power: 11 For the case with Y+=1 have a look in this thread: Why Menter's SST model low-Re issue has not been seriously investigated? For k fixedValue is suggested and for nut calculated (so no wall functions). shereez234 likes this.

 November 6, 2015, 19:42 #3 Senior Member     shereez Join Date: Jan 2014 Location: England Posts: 188 Rep Power: 4 First, my apologies. I should have seen this thread you guided me to. And This reference seems very helpful. Thanks a lot. Will investigate further into this.

 November 10, 2015, 21:36 #4 Senior Member     shereez Join Date: Jan 2014 Location: England Posts: 188 Rep Power: 4 Right Okay. So I gave this a try and suprisingly: it did not seem to work well. I have changed fv schemes around a lot. I am getting bounding omega to be jumping from 1 to a really high value ( 1e58 or may be more) and solution stops. After reading the post you reffered me to: 1) I have mesh for Naca0012 with size = 24,000 elements - hexa - quads. This mesh converges in fluent. Turbulent intensity = 0.05 % and laminar to turbulent ( eddy visc ratio = 0.009) giving me a Omega Wall ( Menter's propsition) = 1.9e08 at the wall(airfoil in this case). Here is my file details: k boundaryField { CRVS { type fixedValue; value uniform 1e-18; } INLET { type turbulentIntensityKineticEnergyInlet; intensity 0.052; value uniform 0.219; omega CRVS { type fixedValue; value uniform 1.9e+008; Cmu 0.09; kappa 0.41; E 9.8; beta1 0.075; } INLET { type inletOutlet; inletValue uniform 0; value uniform 0; Solver: PISOFOAM deltaT 0.000000002; fvschemes ddtSchemes { default backward; } gradSchemes { default leastSquares; grad(p) Gauss linear; grad(U) Gauss linear; } divSchemes { default none; div(phi,U) bounded Gauss upwind; div(phi,k) bounded Gauss upwind; div(phi,omega) bounded Gauss upwind; div((nuEff*dev(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear corrected; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } fluxRequired { default no; p ; Phi ; } fvSolution solvers { p { solver GAMG; tolerance 1e-07; relTol 0.1; smoother GaussSeidel; cacheAgglomeration true; nCellsInCoarsestLevel 10; agglomerator faceAreaPair; mergeLevels 1; maxIter 1000; } pFinal { solver GAMG; tolerance 1e-6; relTol 0; smoother GaussSeidel; } Phi { \$p; } U { solver smoothSolver; smoother GaussSeidel; nSweeps 1; tolerance 1e-08; relTol 0.1; maxIter 1000; } k { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; maxIter 1000; } omega { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; maxIter 1000; } } PISO { nCorrectors 2; nNonOrthogonalCorrectors 0; pRefCell 0; pRefValue 0; residualControl { p 1e-5; U 1e-5; } } potentialFlow { nNonOrthogonalCorrectors 10; pRefCell 0; pRefValue 0; PhiRefCell 0; PhiRefPoint 0; PhiRefValue 0; Phi 0; } relaxationFactors { fields { p 0.1; } equations { U 0.1; omega 0.1; k 0.1; } } Error Message: Time = 1.8e-008 Courant Number mean: 6.6089e+010 max: 5.96403e+018 smoothSolver: Solving for Ux, Initial residual = 0.0854157, Final residual = 0.00162756, No Iterations 2 smoothSolver: Solving for Uy, Initial residual = 0.0857431, Final residual = 0.0083747, No Iterations 1 GAMG: Solving for p, Initial residual = 0.840767, Final residual = 0.0795824, No Iterations 2 time step continuity errors : sum local = 6.50813e+016, global = 1.35752, cumulative = 1.35752 GAMG: Solving for p, Initial residual = 0.996139, Final residual = 8.94264e-007, No Iterations 40 time step continuity errors : sum local = 2.66843e+022, global = 1.26249e+007, cumulative = 1.26249e+007 smoothSolver: Solving for omega, Initial residual = 0.999561, Final residual = 0.0112157, No Iterations 4 bounding omega, min: 0 max: 1.39292e+063 average: 7.77122e+058 smoothSolver: Solving for k, Initial residual = 0.363297, Final residual = 3.7894e-019, No Iterations 1 bounding k, min: 1e-018 max: 33.6809 average: 0.36149 ExecutionTime = 26.234 s ClockTime = 26 s Regards and thanks in advance for any one willing to share ideas and experience.

 November 12, 2015, 03:54 #5 Senior Member     Anton Kidess Join Date: May 2009 Location: Delft, Netherlands Posts: 1,153 Rep Power: 20 Did you carefully read the thread Joachim linked? If so, I'm surprised by your choice of boundary conditions. By the way, please use "[code]" tags to make your post more readable. __________________ *On twitter @akidTwit *Spend as much time formulating your questions as you expect people to spend on their answer. *Join the OpenFOAM stackexchange Q&A site: http://area51.stackexchange.com/prop...oHPxcPqde7HtA2

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