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Higher order Schemes are unstable, Why?

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Old   September 9, 2013, 04:58
Default Higher order Schemes are unstable, Why?
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sivakumar selvaraju
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Hi,
I used Gauss Linear for pressure gradient, the solution is stable, but the results are bit far from the expected, so switched Gauss Linear pressure gradient to leastSquares, the simulation is not stable, to make it stable I have given some limitation to the laplacianSchemes (0.5) for other than pressure, now the solution is stable but the results are not acceptable, it far away from the experimental results.

gradSchemes
{
default Gauss linear;
grad(p) leastSquares;
grad(omega) Gauss linear;
grad(epsilon) Gauss linear;
grad(U) Gauss linear;
grad(k) Gauss linear;
}

divSchemes
{
default none;
div(phi,U) Gauss linearUpwindV grad(U);
div(phi,k) Gauss upwind;
div(phi,omega) Gauss upwind;
div(phi,epsilon) Gauss upwind ;
div((nuEff*dev(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
default none;
laplacian(nuEff,U) Gauss linear limited 0.5;
laplacian((1|A(U)),p) Gauss linear limited 1;
laplacian(1,p) Gauss linear limited 1;
laplacian(DkEff,k) Gauss linear limited 0.5;
laplacian(DepsilonEff,epsilon) Gauss linear limited 0.5;
laplacian(DomegaEff,omega) Gauss linear limited 0.5;
}

interpolationSchemes
{
default linear;
interpolate(U) linear;
}

snGradSchemes
{
default limited 0.5;
}

is there any way to solve this problem?

any suggestions?

Thanks,
Sivakumar
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Old   September 10, 2013, 09:32
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Hrvoje Jasak
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You need to read some CFD books: you are using unbounded convection schemes on bounded variables: this is why the simulations blow up for you.

Hrv
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Old   September 10, 2013, 11:00
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sivakumar selvaraju
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Dear Prof (Hrv),

Thanks for your reply and suggestion.

Thanks,
Sivakumar
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