Instabilities with too low yplus values?
 

Hi,

I'm running a case with the k-omega SST turbulence model without wallfunctions, and are having some trouble with convergence.

From one guide I've read, the yplus values should be below 6. But when I try to fulfill this, I get maximum yplus values around 5-6, and avg. values of around 1, while the minimum values are as low as 0.07.

The problem is that approx. halfway though my simulations the pressure residuals suddenly increase (and stabilizes) at a pretty high level (just below 1.0). I have also tried using a smaller cells, with smaller yplus values, but the same thing happens.

However, if I have a courser mesh, with average yplus values of ~4-5, maximum values of 15, and minimum values of ~0.8, the pressure residual behaves nicely.

I've read somewhere that too small yplus values can cause troubles, and I guess that's what I'm experiencing now ?

Any thoughts?

Cheers