Hi I'm simulating flow throught 2 parallel plates with inclined inlet and outlets. I tried the second order upwind momentum discretization (and also QUICK) but it couldn't converge very well. For example the average velocity in a plane was fluctuaing at around 1% of its maximum value. But when I switched to the first order upwind, this fluctuation is reduced to 0.2%.

I know first order can converge more easily and 2nd order is more accurate. But will a 2nd order solution that is partially converged be more accurate than a 1st order one?

Are there any ways to help the 2nd order solution converge? I have reduced the momemtum under relaxation to 0.3 but to no avail. I was wonder if I should make some changes to the multigrid entries. Any suggestions?

Try to increase the pressure under-relaxation factor to 0.6 or so.

Also consider a grid refinement.

Regards, ap

Unfortunately that didn't work. In fact the integral of the pressure in the system is also fluctuating and can't converge.

Check your grid elements. If they are high skewed that could be the possible reason. Luca

Some of the elements are indeed skewed but I can't do much about it because of the geometry of the domain. Can I work around this by using skewness correction in SIMPLEC or PISO? If so, what is a common value to try?

Just found of that PISO dosen't work. I tried it with and without skewness correctiona and used the QUICK scheme with it.

You should try to correct your grid...I had your same problem and when I remeshed the problem was solved. Luca

I remeshed taking care in reducing the number of skewed elements. It dosen't seem to work. As before, the residuals can't get below 1e-3 when I used 2nd order upwind. Pressure is also fluctuating.

[k_tafazoli]

Hi, I've got a fortran code for solving 2D compressible flow over an airfoil with the method of first order van leer flux vector splitting . I have to change it to second order van leer flux vector splitting method . Can you please help me on how to do it? It's also possible for me to solve this project with the method of AUSM+ . Are you familiar with this method? can you help me with it please?
Thanks a lot in advance