CFD Online Discussion Forums

CFD Online Discussion Forums (
-   CFX (
-   -   SST transitional turbulence model (

Ben Akih June 7, 2006 12:54

SST transitional turbulence model
hi folks, just wondering if anyone here has experience with modelling transition using the 2 eqn sst model. i am trying to simulate the laminar turbulent transition in a mach 7.5 flow over a flat plate. my residuals decrease and oscillate. the omega and the 2 transitional closure equations are especially bad with residuals oscillating around 1e-2. that is my first problem. second problem is when i view the intermediate results, transition occurs very far downstream compared to the experimentally observed transition point. a strange thing is that this position seem to move further downstream with increasing number of iterations. i am using steady state simulation, 1% free stream turbulence degree. i have checked the converged Yplus and it is a little below 1 at the wall, which i guess should not be a problem. would be grateful for some insight. regards, ben.

Joe June 7, 2006 16:55

Re: SST transitional turbulence model
You may need to solve it as a transient problem. There was a monster thread about the transition model some time back. Search the forum for "transition wing" etc.

Chebeba June 8, 2006 13:28

Re: SST transitional turbulence model
Well, I have no experience with supersonic stuff since I work in water, but this is what I've learned. YMMW.

- It seems not to like structured meshes at all.

- It seems to like y+ < 1.0 even at max shear.

- It seems to like mesh expansion lower than 1.2 and lots of layers.

- It seems to like a lot finer mesh than what is suggested in the manual (manual says >70 streamwise nodes are fine, I usually the double.

- It seems to work best with Intensity/Length Scale as the inlet turbulence spec, but it is still very sensitive to the applied values.

- It seems to do a better job at higher angles of attack.


Chebeba June 8, 2006 15:52

Re: SST transitional turbulence model
Oh, and one more thing: It's sensitive to mesh resolution and smoothness at the front of the foil. Like how the fluid hits the leading edge will influence how far down transition occurs.

All times are GMT -4. The time now is 19:08.