[fredo490]

Dear all,
I'm running some simulations with rhoSimplecFoam (k-epsilon, Air) and I encounter some convergence / initialization problems. I mostly run my case at Mach 0.3 and 0.4 and I often get divergence even with simple geometries such as Naca Airfoils or Cylinders.

I tried different techniques:
- initialize the flow with a potentialFoam
- initialize the velocity internalField at different speed (0 to 80m/s)
- play with the under relaxation numbers ...
- using upwind scheme
- use different meshes (structured, unstructured, yPlus from 0.1 to 30,...)

After many tries, I found that a good way to avoid divergence and get convergence is to slowly increase the inlet velocity value ! For example, I start at 2m/s, then 5m/s, then 10m/s and so on until the actual velocity. However, this technique is "slow" and requires some manual change.

First, is this "initialization" ok ? I mean, I didn't see anybody using such a technique, maybe there is a problem I don't know about.

Second, is there a way to make this automatically ? I found this link but it looks old and unusable in OF2: http://www.idurun.com/?p=512

My inlet is:

alphat:
        type            calculated;
        value           uniform 0;

epsilon:
        type            fixedValue;
        value           uniform 2.15e-1;

k:
        type            fixedValue;
        value           uniform 1.6e-2;

mut:
        type            calculated;
        value           uniform 0;

p:
        type            zeroGradient;

T:
        type            fixedValue;
        value           uniform 281.4;

U:
        type            fixedValue;
        value           uniform (81.02 0 0);

My outlet is:

alphat:
        type            calculated;
        value           uniform 0;

epsilon:
        type            inletOutlet;
        inletValue     uniform 2.15e-1;
        value           uniform 2.15e-1;

k:
        type            inletOutlet;
        inletValue     uniform 1.6e-2;
        value           uniform 1.6e-2;

mut:
        type            calculated;
        value           uniform 0;

p:
        type            fixedValue;
        value           uniform 95650;

T:
        type            inletOutlet;
        inletValue     uniform 281.4;
        value           uniform 281.4;

U:
        type            inletOutlet;
        inletValue     uniform (81.02 0 0);
        value           uniform (81.02 0 0);

My wall is:

alphat: 
        type            alphatWallFunction;
        value           uniform 0;

epsilon:
        type            compressible::epsilonWallFunction;
        value           uniform 2.15e-1;

k:
        type            compressible::kqRWallFunction;
        value           uniform 1.6e-2;

mut:
        type            mutkWallFunction;
        value           uniform 0;

p:
        type            zeroGradient;

T:
        type            zeroGradient;

U:
        type            fixedValue;
        value           uniform (0 0 0);

My internalFiel is:

alphat:
        value           uniform 0;

epsilon:
        value           uniform 2.15e-1;

k:
        value           uniform 1.6e-2;

mut:
        value           uniform 0;

p:
        value           uniform 95650;

T:
        value           uniform 281.4;

U:
        value           uniform (81.02 0 0);