Strange residuals simple
 

Hi everybody,

I'm currently creating a RANS model of a cube in the air. I'm in high Re and I'm trying to model the flow around this cube in k-omega-SST.
As you can see in the picture below, my residuals are strange... My residuals react like if I change something in fvSchemes or fvSolution. The model seems to converge and then blows up !
I'm sure of my BC, and k-epsilon works without any problems.
Do you have any ideas or suggestions about my problem ?

Thank you in advance.

Louis

OpenFOAM 2.2.0

This indeed looks like you changed the fvSchemes... Can you tell us a bit more about your setup? What about b.c. and fvSchemes?
Did you have any "bounding errors" in the log file before the blow ups?

Thanks for your reply.

My "bounding error" appear after the blow ups. But only for the "little" blow ups ( approximately times 1600 and 2900), the others don't involve "bounding error"... Despite the fact that they're more important, it's very strange.

Concerning my BC, in inlet I've a logarithmic profile for the velocity (which corresponds to a field data). Same thing for the TKE (Turbulent Kinetic Energy) and omega.

On the wall I keep the wall-functions even if I have my y+ E [0,4].

And for my fvSchemes, this residuals correspond to an upwind resolution. I've tried linearUpwind grad(U), the same blow ups appear... so I keep 1st order for the moment.

Did you try to run the case with constant (fixed value) boundary condition? Maybe the profile is the source of your pain...

I didn't try, I will tomorrow.

But another case that I studied was in low-Re, and exactly the same thing occurred (with inlet fixed value).
It's only with k-omega-sst, my k-epsilon model don't have this problem I don't know why. At that time, I thought it was openFOAM which didn't like the k-omega-sst in low-Re... But I was clearly wrong.

I will try tomorrow to keep a fixed value in inlet, I will let you know if it works. If not, you will have to find another solution for me ;)

I just recalled, that i saw exactly what happend in your case, when i had bad posed periodic b.c. Do you use any periodics at all?

When you say periodic b.c, you mean like a velocity which change periodically during the simulation ?
Sorry, but I have never used this kind of b.c... maybe an option is wrong.

I'm going to try with a fixed value at the inlet, if it works, it might be the logarithmic profile which is wrong.

In "0/U" at the inlet I have :

inlet
{
type timeVaryingMappedFixedValue;
setAverage off;
offset (0 0 0);
}

And my velocity profile is in "constant/boundaryData/inlet/0/U". This is well read by OpenFOAM, I find a good profile at the inlet of my system. Omega get the same option.

Well... I don't know really why, but I've found my problem.

First I've tried a fixed value at the inlet, it's doing the same thing than before...

To make the convergence more easy for my model, I've initialize my model with low-Re, and then I increased it (otherwise it blows up).

This morning I tried another way to make my model converged, I've resolved it with y+ ~ 100, and then I've used mapFields to paste my solution on my heavy mesh (y+ ~ 1).

It seems that the blow ups on my residuals are linked to my mesh or k-omega in low-Re, I don't really know, maybe twice.

Well... Rodriguez thanks for your help !

Good continuation, and if one day I've another problem, I'll keep you informed ;)

Great to hear that!