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2D cylinder simulation

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Old   April 5, 2024, 18:32
Default 2D cylinder simulation
  #1
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aaron LLoyd
Join Date: Apr 2024
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I am simulating an incompressible external flow 2D circular cylinder. I know that it is a “classical” example but I haven`t been able to find a similar case online to improve my results in order to obtain the most liable/precise simulation.
My Reynolds number is 2.4 x10^4 and I should get a Cd = 1.2. Instead I am obtaining a higher value (1,43 in average).
I used snappyHexMesh to generate the mesh and then extrudeMesh, I tried several trials changing layers (number, thickness, conformation) and mesh. In all cases the max value of y+ was <1.
I am attaching the results of a simulation in which there were 40 layers and average y+=0.17 and max y+ = 0.32.
The code below refers to the 0 folder boundary conditions k, nut, omega, p, U
k
Code:
 
 
 dimensions      [0 2 -2 0 0 0 0];
 
 
 internalField   uniform 0.0294;
 
 
 boundaryField
 {
     inlet
     {
         type            fixedValue;
         value           uniform 0.0294;
     }
     outlet
     {
         type            inletOutlet;
         inletValue      uniform 0.0294;
         value           uniform 0.0294;
     }
     left
     {
         type            symmetryPlane;
     }
     right
     {
         type            symmetryPlane;
     }
     top
     {
         type            empty;
     }
     bottom
     {
         type            empty;
     }
     cylinder
     {
         type            fixedValue;
         value           uniform 1e-10;
     }
 }
nut
Code:
 
 
 dimensions      [0 2 -1 0 0 0 0];
 
 
 internalField   uniform 0;
 
 
 boundaryField
 {
     inlet
     {
         type            calculated;
         value           uniform 0;
     }
     outlet
     {
         type            calculated;
         value           uniform 0;
     }
     left
     {
         type            symmetryPlane;
     }
     right
     {
         type            symmetryPlane;
     }
     top
     {
         type            empty;
     }
     bottom
     {
         type            empty;
     }
     cylinder
     {
         type            calculated;
         value           uniform 0;
     }
 }
omega
Code:
 
 
 dimensions      [0 0 -1 0 0 0 0];
 
 
 internalField   uniform 164;
 
 
 boundaryField
 {
     inlet
     {
         type            fixedValue;
         value           uniform 164;
     }
     outlet
     {
         type            inletOutlet;
         inletValue      uniform 164;
         value           uniform 164;
     }
     left
     {
         type            symmetryPlane;
     }
     right
     {
         type            symmetryPlane;
     }
     top
     {
         type            empty;
     }
     bottom
     {
         type            empty;
     }
     cylinder
     {
         type            omegaWallFunction;
         value           uniform 164;
     }
 }

p
Code:
 
 
 dimensions      [0 2 -2 0 0 0 0];
 
 
 internalField   uniform 0;
 
 
 boundaryField
 {
     inlet
     {
         type            zeroGradient;
     }
     outlet
     {
         type            fixedValue;
         value           uniform 0;
     }
     left
     {
         type            symmetryPlane;
     }
     right
     {
         type            symmetryPlane;
     }
     top
     {
         type            empty;
     }
     bottom
     {
         type            empty;
     }
     cylinder
     {
         type            zeroGradient;
     }
 }
and U


Code:
 
 
 dimensions      [0 1 -1 0 0 0 0];
 
 
 internalField   uniform (14 0 0);
 
 
 boundaryField
 {
     inlet
     {
         type            fixedValue;
         value           uniform (14 0 0);
     }
     outlet
     {
         type            inletOutlet;
         inletValue      uniform (0 0 0);
         value           uniform (14 0 0);
     }
     left
     {
         type            symmetryPlane;
     }
     right
     {
         type            symmetryPlane;
     }
     top
     {
         type            empty;
     }
     bottom
     {
         type            empty;
     }
     cylinder
     {
         type            fixedValue;
         value           uniform (0 0 0);
     }
 }

and controlDict
Code:
 application     pimpleFoam;
 
 
 startFrom       latestTime;
 
 
 stopAt          endTime;
 
 
 endTime         100;
 
 
 deltaT          0.00001;
 
 
 writeControl    adjustable;
 
 
 writeInterval   0.001;
 
 
 purgeWrite      1;
 
 
 writeFormat     binary;
 
 
 writePrecision  7;
 
 
 writeCompression no;
 
 
 timeFormat      general;
 
 
 timePrecision   6;
 
 
 runTimeModifiable yes;
 
 
 adjustTimeStep  yes;
 
 
 maxCo           0.9;
 
 
 functions
 {
     #include "forces"
     #include "forceCoeffs"
     #include "yPlus1"
     #include "pressureCoefficient"
     #include "wallShearStress"
     #include "Q"
     #include "wallBoundedStreamLine"
 }
and fvSchemes


Code:
 ddtSchemes
 {
     default         CrankNicolson 0.9;
 }
 
 
 gradSchemes
 {
     default         Gauss linear;
 
 
 }
 
 
 divSchemes
 {
     default         none;
 
 
     div(phi,U)      Gauss linear;
     div(phi,k)      Gauss upwind;
     div(phi,omega)  Gauss upwind;
 
 
     div((nuEff*dev2(T(grad(U))))) Gauss linear;
 }
 
 
 laplacianSchemes
 {
     default         Gauss linear limited 1.0;
 }
 
 
 interpolationSchemes
 {
     default         linear;
 }
 
 
 snGradSchemes
 {
     default         limited 1.0;
 }
 
 
 wallDist
 {
     method          meshWave;
 }
and fvSolution


Code:
  solvers
 {
     p
     {
         solver          GAMG;
         smoother        GaussSeidel;
         tolerance       1e-6;
         relTol          0.01;
     }
 
 
 
 
     pFinal
     {
         solver          GAMG;
         smoother        GaussSeidel;
         tolerance       1e-8;
         relTol          0;
     }
 
 
    
     U    
     {
         solver          smoothSolver;
         smoother        symGaussSeidel;
         tolerance       1e-8;
         relTol          0.1;
     }
 
 
     UFinal
     {
        $U;
        relTol      0;
     }
 
 
     k    
     {
         solver          smoothSolver;
         smoother        symGaussSeidel;
         tolerance       1e-8;
         relTol          0.1;
     }
 
 
    kFinal
     {
        $U;
        relTol      0;
     }
 
 
     omega    
     {
         solver          smoothSolver;
         smoother        symGaussSeidel;
         tolerance       1e-8;
         relTol          0.1;
     }
 
 
     omegaFinal
     {
        $U;
        relTol      0;
     }
 
 
 
 
 }
 
 
 PIMPLE
 {
 
 
     nCorrectors              2;
 
 
     nNonOrthogonalCorrectors 1;
 
 
     nOuterCorrectors    1;
 
 
 }
I am attaching a screenshot of the mesh and the images of the results: RESIDUAL(Ux, Uy, p) and Cd. The chart shows the final period as the simulation appears already for a while convergent.
Attached Images
File Type: jpg Cd.jpg (30.7 KB, 7 views)
File Type: jpg Residual.jpg (60.7 KB, 11 views)
File Type: png mesh.png (169.0 KB, 9 views)
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Old   April 6, 2024, 06:21
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  #2
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ROIN bin
Join Date: Dec 2019
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It looks very close, I think we can adjust the calculation area and boundary conditions (such as outlet), and I noticed that you used the built-in post-processing tool to output the coefficient, perhaps test it with force.
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Old   April 6, 2024, 11:36
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aaron LLoyd
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Thanks for your reply and help: let me try to answer. In forceCoeffs lRef= 0.0272 which corresponds to the diameter of the cylinder,
and Aref= 0.00272 since I set thikness= 0.1 in extrudeMesh.
In the postProcessing folder, taking the Cd value at time 0.4, as an example,
I have Cd= 1.5499957, and taking at the same time the value of the Total force
= Pressure + Viscous in the x direction = 5.0612938e-01.
F= 1/2*1.225*14^2*0.00272*1.5499957 which gives a slightly different value:
0.506116759, but this difference seems negligible to me .
As for the outlet boundary conditions I just tried to
replace in k and omega &quot;type inletOutlet&quot; with &quot;type zeroGradient&quot;, but I haven`t
seen any change.
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Old   April 10, 2024, 09:21
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aaron LLoyd
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Hi, can anyone give me an advice? I would really appreciate it
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