Pressure Far Field Boundary for low Mach Numbers

HorstvanGrass · May 14, 2019, 15:26

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, 16:05

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, 15:26	Pressure Far Field Boundary for low Mach Numbers	#1
HorstvanGrass Member Horst van Gras Join Date: Oct 2018 Posts: 45 Rep Power: 8	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!

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Multiphase flow - incorrect velocity on inlet	Mike_Tom	CFX	6	September 29, 2016 02:27
Radiation interface	hinca	CFX	15	January 26, 2014 18:11
An error has occurred in cfx5solve:	volo87	CFX	5	June 14, 2013 18:44
Low Mixing time Problem	Mavier	CFX	5	April 29, 2013 01:00
RPM in Wind Turbine	Pankaj	CFX	9	November 23, 2009 05:05

May 15, 2019, 16:05		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,754 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.