Simulation for Reynolds number of 10 and Knudsen number of 0.1

Astro10 · April 28, 2018, 16:28

Hello,

Which software/model should be used for a Reynolds number of 10 and Knudsen number of 0.1?

Thanks

LuckyTran · April 29, 2018, 20:29

Can you maybe describe what are the physics you want to simulate?

Re = 10 is that laminar or turbulent? Kn = 0.1 means continuum hypothesis holds right? Virtually any CFD solver can handle continuum flows... And just about any CFD solver can handle laminar flows.

Astro10 · April 30, 2018, 08:20

This is a gas flow into a vacuum. The inlet will have a high reynolds number while the flow into the vacuum is very low. It should be mostly laminar?

flotus1 · April 30, 2018, 08:32

For Kn=0.1, continuum hypothesis is no longer valid.
You can stretch it a bit by using slip boundary conditions (aka Maxwell boundary condition) for velocity and temperature at solid walls, depending on how accurate your results need to be.
Most CFD packages have this type of boundary condition already implemented or allow you to implement it yourself.

The correct approach would probably be DSMC. Given that the Mach number should be fairly high for a flow into vacuum, it should be feasible from a computational point of view. The computational cost for standard DSMC is proportional to 1/Ma².
IIRC there is an extension for OpenFOAM based on DSMC, but I never used it.

April 28, 2018, 16:28	Simulation for Reynolds number of 10 and Knudsen number of 0.1	#1
Astro10 New Member Bob Join Date: Apr 2016 Posts: 3 Rep Power: 10	Hello, Which software/model should be used for a Reynolds number of 10 and Knudsen number of 0.1? Thanks

April 29, 2018, 20:29		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,675 Rep Power: 66	Can you maybe describe what are the physics you want to simulate? Re = 10 is that laminar or turbulent? Kn = 0.1 means continuum hypothesis holds right? Virtually any CFD solver can handle continuum flows... And just about any CFD solver can handle laminar flows.

April 30, 2018, 08:20		#3
Astro10 New Member Bob Join Date: Apr 2016 Posts: 3 Rep Power: 10	This is a gas flow into a vacuum. The inlet will have a high reynolds number while the flow into the vacuum is very low. It should be mostly laminar?

April 30, 2018, 08:32		#4
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	For Kn=0.1, continuum hypothesis is no longer valid. You can stretch it a bit by using slip boundary conditions (aka Maxwell boundary condition) for velocity and temperature at solid walls, depending on how accurate your results need to be. Most CFD packages have this type of boundary condition already implemented or allow you to implement it yourself. The correct approach would probably be DSMC. Given that the Mach number should be fairly high for a flow into vacuum, it should be feasible from a computational point of view. The computational cost for standard DSMC is proportional to 1/Ma². IIRC there is an extension for OpenFOAM based on DSMC, but I never used it.