[santos]

Hello

I wonder if anyone can give some advice on this problem:

I am simulating a rectangular cross section channel with dimensions 11.4 x 2 x 30 (mm). Reynolds number is 250 (based on channel height) for water flowing at room temperature.

For this Re number, the flow regime is expected to be transient.

The inlet and outlet are specified as cyclic.
The time step was set in order to maintain Courant number smaller than 1.

The solver is channelOodles.

My fvSchemes file content is the following:
ddtSchemes
{
default Euler;
}

gradSchemes
{
default Gauss linear;
grad(p) Gauss linear;
grad(U) Gauss linear;
}

divSchemes
{
default none;
div(phi,U) Gauss QUICK;
div(phi,k) Gauss limitedLinear 1;
div(phi,B) Gauss limitedLinear 1;
div(B) Gauss linear;
div(phi,nuTilda) Gauss limitedLinear 1;
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(DBEff,B) Gauss linear corrected;
laplacian(DnuTildaEff,nuTilda) Gauss linear corrected;
}

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

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p;
}

I am using BICCG for the velocity and AMG for the pressure (2 PISO correctors), with 100 cells on the top level.

With this settings, the simulation diverges (NaN) randomly. This happens regardless of the mesh refinement - I get the same behaviour for 65k, 125k, 500k and 1M cells.

As soon as I change the velocity scheme from QUICK to Gamma or linear, I stop observing the divergence problems.

Is this an intrinsic problem of using the QUICK scheme (however, it is the most used scheme in the literature on the same kind of simulations, using either CFX or Fluent), or is it a bug?

On the other hand, is Gamma scheme at least equivalent in accuracy to QUICK so it can be used instead?

Thanks a lot!

Regards
José Santos