Which model can I use instead of RNG k-E and get good pressures?
 

Hallo,

Which turbulent model should I use instead of RNG k-E and get good pressures on the building facades? I had good results and good convergence while windward wall was parallel to Inlet plane and when the building is turned for 15 degrees.
But when the angle is 30 or 45 degrees RNG has really bad convergence and not stable solution.

Thanks,
Danijela

You change turbulence models because of accuracy issues, not numerical stability issues.

I would recommend you use the SST turbulence model unless you have a good reason to do otherwise.

If you are having troubles getting convergence look at this FAQ: http://www.cfd-online.com/Wiki/Ansys...gence_criteria

Thanks Glenn
for suggestion. I used also SST besides K-Omega for some previous models but usually for initializaion file. And SST gives better pressures on the building facades then k-Omega. The RNG has the best one.
the thing is that the approach I had for cases when building is 0 and 15 degree turned can not be applied for 30 and 45 degrees. With the same approach (probably mesh is the main thing) I can get only 10e-3 or 10e-4 (RMS) much worse then for first two cases.

Have you read the FAQ? It tells you everything you need to know about this issue.

Yes I did :) not once :) but most of advices consider transient analysis and I have steady state. But this was interesting ' If these parameters are not changing to an accuracy tolerance suitable for your simulation then your simulation is almost certainly OK'. I was monitoring the velocity and pressure and they oscilate. So I stopped analysis in the maximum and minimum and compared... :) the difference is not big up to 2.5%, in one point it is 5 and on leeward wall is 16%. well I have to check if I stopped it in the right moment :):rolleyes:

You did not read it very carefully then - it is written for when a steady state simulation does not converge. That is the title. The transient simulation is simply one of the options to obtain convergence if it is particularly stubborn - but it still applies to a steady state simulation.

The best thing to do to monitor convergence like this is to have monitor points with CEL expressions which calculate your parameter of interest. Then you can watch the convergence of them as the simulation progresses and you do not need to stop it to see how it is going.