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October 24, 2021, 05:56 |
Why do probes always sample the same value?
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#1 | |||
New Member
Ali Can
Join Date: Apr 2021
Posts: 28
Rep Power: 5 |
Hi all,
Firstly, I am simulating the cavity flow with and without doors at 0.85 Mach. I have successfully completed the "without doors" analysis. However, in with doors case, I have a problem with probes that sample pressure value at every time step. My initial pressure value is 62100Pa. After some time steps, probes start to measure the same pressure value which is equal to half of the initial value until the end of the analysis. I have tried different schemes but the results are the same. When I check the mesh quality, everything seems ok. In "without doors" case probes were quite successful to catch pressure fluctuations but "with doors" case probes don't catch the pressure fluctuations. What could be the problem? thanks in advance.. Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: v1912 | | \\ / A nd | Website: www.openfoam.com | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class polyBoundaryMesh; location "constant/polyMesh"; object boundary; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // 7 ( back { type symmetry; inGroups 1(symmetry); nFaces 393600; startFace 81097200; } door { type wall; inGroups 1(walls); nFaces 75200; startFace 81490800; } front { type patch; inGroups 1(farfield); nFaces 304000; startFace 81566000; } inlet { type patch; inGroups 1(farfield); nFaces 6400; startFace 81870000; } outlet { type patch; inGroups 1(farfield); nFaces 6400; startFace 81876400; } top { type patch; inGroups 1(farfield); nFaces 304000; startFace 81882800; } wall { type wall; inGroups 1(walls); nFaces 396000; startFace 82186800; } ) // ************************************************************************* // Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: v1912 | | \\ / A nd | Website: www.openfoam.com | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; location "system"; object fvSolution; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // solvers { "(p|rho)" { solver PCG; preconditioner DIC; tolerance 1e-6; relTol 0.01; } "(p|rho)Final" { $p; relTol 0; } "(U|k|e)" { solver smoothSolver; smoother symGaussSeidel; tolerance 1e-6; relTol 0.01; } "(U|k|e)Final" { $U; relTol 0; } "(U|k|B|nuTilda)" { solver smoothSolver; smoother symGaussSeidel; tolerance 1e-7; relTol 0; } "(U|k|B|nuTilda)Final" { $U; relTol 0; } } PIMPLE { momentumPredictor yes; nOuterCorrectors 2; nCorrectors 2; // 1 nNonOrthogonalCorrectors 1; pMinFactor 0.5; pMaxFactor 2.0; } relaxationFactors { equations { ".*" 1; } } // ************************************************************************* // Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: v1912 | | \\ / A nd | Website: www.openfoam.com | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; location "system"; object fvSchemes; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // ddtSchemes { default backward; } gradSchemes { default Gauss linear; } divSchemes { default none; div(phi,U) Gauss linearUpwind grad(U); div(phi,e) Gauss limitedLinear 1; div(phi,K) Gauss limitedLinear 1; div(phiv,p) Gauss limitedLinear 1; div(phi,k) Gauss limitedLinear 1; div(phi,B) Gauss limitedLinear 1; div(B) Gauss linear; div(phi,nuTilda) Gauss limitedLinear 1; div(((rho*nuEff)*dev2(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear corrected; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } wallDist { method meshWave; } // ************************************************************************* // Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: v1912 | | \\ / A nd | Website: www.openfoam.com | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; object controlDict; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // application rhoPimpleFoam; startFrom latestTime; startTime 0; stopAt endTime; endTime 0.0625; deltaT 1.76e-6; writeControl adjustable; writeInterval 0.0125; purgeWrite 0; writeFormat ascii; writePrecision 6; writeCompression off; timeFormat general; timePrecision 6; runTimeModifiable true; functions { #includeFunc MachNo #includeFunc residuals probes { type probes; libs ("libsampling.so"); writeControl runTime; writeInterval 1.76e-6; fields ( p ); probeLocations ( (0.0254 0 0) (0.0762 0 0) (0.1270 0 0) (0.1778 0 0) (0.2286 0 0) (0.2794 0 0) (0.3302 0 0) (0.3810 0 0) (0.4318 0 0) (0.4826 0 0) ); } } // ************************************************************************* // Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: v1912 | | \\ / A nd | Website: www.openfoam.com | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; location "constant"; object turbulenceProperties; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // simulationType LES; LES { LESModel SpalartAllmarasDDES; delta vanDriest; printCoeffs on; turbulence on; cubeRootVolCoeffs { deltaCoeff 1; } laminarCoeffs { } oneEqEddyCoeffs { ck 0.07; ce 1.05; } dynOneEqEddyCoeffs { ce 1.05; filter simple; } locDynOneEqEddyCoeffs { ce 1.05; filter simple; } SmagorinskyCoeffs { ce 1.05; ck 0.07; } Smagorinsky2Coeffs { ce 1.05; ck 0.07; cD2 0.02; } spectEddyViscCoeffs { ce 1.05; cB 8.22; cK1 0.83; cK2 1.03; cK3 4.75; cK4 2.55; } dynSmagorinskyCoeffs { ce 1.05; filter simple; } mixedSmagorinskyCoeffs { ce 1.05; ck 0.07; filter simple; } dynMixedSmagorinskyCoeffs { ce 1.05; filter simple; } LRRDiffStressCoeffs { ce 1.05; ck 0.09; c1 1.8; c2 0.6; } DeardorffDiffStressCoeffs { ce 1.05; ck 0.09; cm 4.13; } SpalartAllmarasCoeffs { alphaNut 1.5; Cb1 0.1355; Cb2 0.622; Cw2 0.3; Cw3 2; Cv1 7.1; Cv2 5.0; CDES 0.65; ck 0.07; } SpalartAllmarasDDESCoeffs { alphaNut 1.5; Cb1 0.1355; Cb2 0.622; Cw2 0.3; Cw3 2.0; Cv1 7.1; Cv2 5.0; CDES 0.65; ck 0.07; } SpalartAllmarasIDDESCoeffs { delta IDDESDelta; IDDESDeltaCoeffs { deltaCoeff 1; //according to src/turbulenceModels/incompressible/LES/SpalartAllmarasIDDES/IDDESDelta/IDDESDelta.C cw 0.15; } alphaNut 1.5; kappa 0.4187; Cb1 0.1355; Cb2 0.622; Cw2 0.3; Cw3 2.0; Cv1 7.1; Cv2 5.0; CDES 0.65; ck 0.07; //These are the default values sigmaNut 0.66666; kappa 0.41; Cb1 0.1355; Cb2 0.622; Cv1 7.1; Cv2 5; CDES 0.65; ck 0.07; Cw2 0.3; Cw3 2; fwStar 0.424; cl 3.55; ct 1.63; } cubeRootVolCoeffs { deltaCoeff 1; } PrandtlCoeffs { delta cubeRootVol; cubeRootVolCoeffs { deltaCoeff 1; } smoothCoeffs { delta cubeRootVol; cubeRootVolCoeffs { deltaCoeff 1; } maxDeltaRatio 1.1; } Cdelta 0.158; } vanDriestCoeffs { delta cubeRootVol; cubeRootVolCoeffs { deltaCoeff 1; } smoothCoeffs { delta cubeRootVol; cubeRootVolCoeffs { deltaCoeff 1; } maxDeltaRatio 1.1; } Aplus 26; Cdelta 0.158; } smoothCoeffs { delta cubeRootVol; cubeRootVolCoeffs { deltaCoeff 1; } maxDeltaRatio 1.1; } kappa 0.4187; wallFunctionCoeffs { E 9; } } // ************************************************************************* // Quote:
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October 26, 2021, 04:12 |
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#2 |
Senior Member
Join Date: Dec 2019
Posts: 215
Rep Power: 7 |
Where are your probes located? An image might change.
Do the physical fields change after that timestep? I suppose its rather not a problem with the sampling, since usually it works flawlessly. |
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October 26, 2021, 05:11 |
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#3 |
New Member
Ali Can
Join Date: Apr 2021
Posts: 28
Rep Power: 5 |
Firstly I would like to thank you for your reply,
My probes are located on the cavity floor (can be seen in the figure). In the "without doors" case my everything was fine, like you said probably it is not a problem with sampling... I checked the physical fields, freestream value starts with 278m/s and suddenly drops to very small values such as 1, 2.. However, my pressure value seems half of the initial pressure value again. I carried out another simulation using a different turbulence model and the same pressure value was measured very long time. After very long time pressure fluctuations commenced but fluctuations are about only 1-2 pascal. Is it a good idea to extend the end time of the analysis? I'm stuck on this problem. thanks in advance.. |
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October 26, 2021, 05:23 |
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#4 |
Senior Member
Join Date: Dec 2019
Posts: 215
Rep Power: 7 |
I have just now checked your BCs.
Things that might be a problem: 1. I see no inlet BC for U. Maybe its a copy paste error, since otherwise the simulation wouldnt even start? 2. You are setting the inlet for p to zeroGradient and the outlet to wavetransmissive. Depending on your inletBC for U, they might not form a closed system. You should try the following: either p and U as fixedValue at the inlet and the outlet waveTransmissive for p and U or totalPresse and pressureInletOutletVelocity for U at the inlet and for p and U waveTransmissive at the outlet or you try a massFlowRate-BC for U at the inlet. I think then setting p to zeroGradient is fine. |
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