Pressure Far Field Boundary for low Mach Numbers

HorstvanGrass · May 14, 2019, 14:26

Hi there,
ist there a minimum for the Mach number in pressure far field boundary condition? Because for Pressure 90000 and Mach 0.1 there is no chance for convergence. Increased quality and simplified the mesh but residuals won't decrese. By looking for residuals contours of velocity and turbulance modell, they are very high in the complete mesh, what I find doesn't make so much sense. With a badder mesh and Mach over 0.3 it's super easy converging.
So is it possible that's I have to refine it so much to get the little compressible effects or is it just not possible with this boundary condition.

Thx in advance!

LuckyTran · May 15, 2019, 15:05

There isn't a low mach number limit.

You have a general problem unrelated to the type of boundary condition. Maybe your initial condition is bad or your solver settings not tuned. But it's not because the boundary condition is not working. Whatever you are doing, you got lucky with the higher Mach numbers and unlucky with the super low Mach numbers.

May 14, 2019, 14:26	Pressure Far Field Boundary for low Mach Numbers	#1
HorstvanGrass Member Horst van Gras Join Date: Oct 2018 Posts: 45 Rep Power: 7	Hi there, ist there a minimum for the Mach number in pressure far field boundary condition? Because for Pressure 90000 and Mach 0.1 there is no chance for convergence. Increased quality and simplified the mesh but residuals won't decrese. By looking for residuals contours of velocity and turbulance modell, they are very high in the complete mesh, what I find doesn't make so much sense. With a badder mesh and Mach over 0.3 it's super easy converging. So is it possible that's I have to refine it so much to get the little compressible effects or is it just not possible with this boundary condition. Thx in advance!

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May 15, 2019, 15:05		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,676 Rep Power: 66	There isn't a low mach number limit. You have a general problem unrelated to the type of boundary condition. Maybe your initial condition is bad or your solver settings not tuned. But it's not because the boundary condition is not working. Whatever you are doing, you got lucky with the higher Mach numbers and unlucky with the super low Mach numbers.