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-   -   problem with torque calc (http://www.cfd-online.com/Forums/openfoam-solving/64991-problem-torque-calc.html)

yuhai May 31, 2009 06:46

problem with torque calc
 
Dear foamers,
I am now calculating the torque of a turbine driven by wind power, with turbDymFoam.
at a higher rotating speed, the torque shows a perfect fit with the experiementation data.
while, at lower rotating speed, the torque coeff is 20% lower than experimentation data.
Can you give some hints for this?


cheers.

henrik May 31, 2009 08:06

Dear Yuhai,

the information you are offering to solve the problem is far from exhaustive. Could this be problem related to the turbulence modelling you use?

Henrik

yuhai May 31, 2009 09:41

1 Attachment(s)
Quote:

Originally Posted by henrik (Post 217718)
Dear Yuhai,

the information you are offering to solve the problem is far from exhaustive. Could this be problem related to the turbulence modelling you use?

Henrik

oh, yes, sorry, I am lack of information.
I am now using the standard k-epsilon with values of k and e, that work fine in Fluent, What I mean is that I used same model and k/e value in OpenFOAM and Fluent, but at lower rotating speed, they give a difference of 20%, while quite alike at higher rotating speed.
I have also tried RNG and SST, but the result is unacceptable for my current k/e/w value. For RNG and SST is not conducted in Fluent, I can't make a compare.

hier is some setting in fvScheme:


ddtSchemes
{
default Euler;
}
gradSchemes
{
default leastSquares;
grad(p) leastSquares;
grad(U) leastSquares;
}
divSchemes
{
default none;
div(phi,U) Gauss upwind;
div(phi,k) Gauss upwind;
div(phi,epsilon) Gauss upwind;
div(phi,omega) Gauss upwind;
div(phi,R) Gauss upwind;
div(R) Gauss linear;
div(phi,nuTilda) Gauss upwind;
div((nuEff*dev(grad(U).T()))) Gauss linear;
}
laplacianSchemes
{
default none;
laplacian(nuEff,U) Gauss linear corrected;
laplacian((1|A(U)),p) Gauss linear corrected;
laplacian(DkEff,k) Gauss linear corrected;
laplacian(DepsilonEff,epsilon) Gauss linear corrected;
laplacian(DREff,R) Gauss linear corrected;
laplacian(DnuTildaEff,nuTilda) Gauss linear corrected;
laplacian(DomegaEff,omega) Gauss linear corrected;
laplacian((rho*(1|A(U))),p) Gauss linear corrected;
laplacian(alphaEff,h) Gauss linear corrected;
laplacian(rAU,p) Gauss linear corrected;
}
interpolationSchemes
{
default linear;
interpolate(U) linear;
}
snGradSchemes
{
default corrected;
}
fluxRequired
{
default no;
p;
}


the air flow is from left side to the turbine. wind speed 10m/s.
while I got fine result at angular velocity = 14, but not at av=8.
I am now wondering whether should I calculate different Re and k/e for different angular velocity?

Best Regards.


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