High Pressure and Turbulence

AndyR · July 14, 2020, 15:27

Folks,
I have a high pressure device flowing air through a series of baffles.
Working pressure around 2000psi
I am using ideal gas law and Standard K-Epsilon.
Max Mach number around 0.2
I am running into the TVR limiter almost everywhere.
Mass and pressure seem well converged.
But the turbulent viscosity field seems unrealistic.
I would expect high values in the baffles themselves, but not in some of the low velocity regions.

Is there a pressure dependency to the turbulent viscosity I am not understanding. IE should I just set the limiter an order (or two) of magnitude higher.
Andy

cwl · July 15, 2020, 01:26

Might be coarse mesh.

AndyR · July 15, 2020, 12:07

It may be a mesh density issue.
However, I am wondering if this is related to density through the normal stress.
As I recall (and I may be a bit out of date here) Star's (and other's) implementation of K-E results in an unphysical turbulent viscosity in regions of high normal stress. And as the K term is per unit mass, and I have a high density (at least for a gas) so perhaps that overshoot due to normal stress is magnified.
I am going to try increasing the mesh density a bit (have to keep the run time finite ;-) and perhaps shift to the realizable KE.

Not a high swirl device but may even try RSM

Any other thoughts out there?
AndyR

July 14, 2020, 15:27	High Pressure and Turbulence	#1
AndyR Member Andy Robertson Join Date: Mar 2009 Location: Long Island NY Posts: 46 Rep Power: 17	Folks, I have a high pressure device flowing air through a series of baffles. Working pressure around 2000psi I am using ideal gas law and Standard K-Epsilon. Max Mach number around 0.2 I am running into the TVR limiter almost everywhere. Mass and pressure seem well converged. But the turbulent viscosity field seems unrealistic. I would expect high values in the baffles themselves, but not in some of the low velocity regions. Is there a pressure dependency to the turbulent viscosity I am not understanding. IE should I just set the limiter an order (or two) of magnitude higher. Andy

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July 15, 2020, 01:26		#2
cwl Senior Member Chaotic Water Join Date: Jul 2012 Location: Elgrin Fau Posts: 435 Rep Power: 17	Might be coarse mesh.

July 15, 2020, 12:07		#3
AndyR Member Andy Robertson Join Date: Mar 2009 Location: Long Island NY Posts: 46 Rep Power: 17	It may be a mesh density issue. However, I am wondering if this is related to density through the normal stress. As I recall (and I may be a bit out of date here) Star's (and other's) implementation of K-E results in an unphysical turbulent viscosity in regions of high normal stress. And as the K term is per unit mass, and I have a high density (at least for a gas) so perhaps that overshoot due to normal stress is magnified. I am going to try increasing the mesh density a bit (have to keep the run time finite ;-) and perhaps shift to the realizable KE. Not a high swirl device but may even try RSM Any other thoughts out there? AndyR