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-   -   Convectiondominated schemes (https://www.cfd-online.com/Forums/openfoam-solving/59151-convectiondominated-schemes.html)

dak81 February 10, 2008 12:09

Hi, All! Please, answer my
 
Hi, All!

Please, answer my question. Is it possible to
solve the convection-diffusion equation with OpenFOAM when convection is dominated?

hjasak February 10, 2008 12:22

Yes - in fact, it is quite eas
 
Yes - in fact, it is quite easy.

dak81 February 10, 2008 12:58

Thanks for the answer. But cou
 
Thanks for the answer. But could you point to my mistake? I was doing so:

solve(- fvm::laplacian(T) + (u & fvc::grad(T)) == f);

where T - temperature

u - predefined analytical velocity field with multiplier alpha, so u = alpha*b,
where b - some vector field with div b = 0

f - source term calculated from the equation by substitution some analytical function theta satisfying boundary condition for T

so when alpha is small enough (<< 1)
residual = T - theta is tolerable, but
when alpha is >> 1, i obtain something wrong
solution which differs from theta very much.

Be glad to hear any suggestions from you. Thanks.

hjasak February 10, 2008 15:33

Did you every look at scalarTr
 
Did you every look at scalarTransportFoam? This is where you should start from:

solve
(
fvm::ddt(T)
+ fvm::div(phi, T)
- fvm::laplacian(DT, T)
);


Hrv

dak81 February 10, 2008 17:37

I've tested your suggestion. I
 
I've tested your suggestion. It has improved my solution but not enough. I've two problems now:
1) it is not clear how small deltaT need to be choosen to obtain stationary solution;
2) while modeling the solution become unstable on some time step i.e. after some time step an absolute residual become growing up.

Any ideas? And what is the best interpolation scheme for my case? I've noticed filteredLiear to be better than limitedLinear.


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