rhoCentralFoam low Ma

VSass · March 20, 2013, 15:48

Hey lads,

i'm trying to simulate a flow of U=0.01m/s around a sphere (Re=183). I've already done this with icoFoam and now i'm trying to get the same results using rhoCentralFoam, but the problem do not seem to converge.

I've read somewhere that this solver needs preconditioning in order to solve for low Ma speeds. Is that why i don't get a similar,converged solution like the one in icoFoam?

Thanks

chriss85 · July 3, 2015, 10:41

Sorry for the late reply, just thought I might add something.

Generally, density based solvers like rhoCentralFoam are not suited for very low Mach number flows, like you appear to have. It's better suited for transsonic/supersonic scenarios. For subsonic cases pressure based solvers are more reliable.

However, I too would like to know up to which lower Mach value the rhoCentralFoam solver is deemed suitable.

AshwaniAssam · July 5, 2015, 01:33

rhoCentralFoam being a density based solver can not be directly used for low mach number as mentioned by Chriss. The solver does not have preconditioning or other low-mach number technique.

I am not sure much about the limit but it could be above M =0.3 . Also, You should not be even getting an accurate solution. Are you getting correct result?

chriss85 · July 6, 2015, 04:50

Do you happen to have some literature regarding preconditioning techniques or other concepts for low Mach numbers in density based solvers?

I'm solving a transient problem in which I can get quite different speeds and Mach numbers (large range of temperatures, and so I also get very different speeds of sounds). I'm not really sure which solver would be best for this. Right now I've based my code on sonicFoam, but sonicFoam is known to perform badly on transsonic/supersonic speeds compared to rhoCentralFoam.

AshwaniAssam · July 6, 2015, 14:01

Did you tried sonicFoam for subsonic cases. It is a pressure-based alogo, it should be working fine. For Preconditioning you can see Blazek CFD book, or just google weiss preconditioning.

chriss85 · July 7, 2015, 04:59

Yes I'm currently using a solver based on sonicFoam. I just want to make sure it's the optimal choice for me

March 20, 2013, 15:48	rhoCentralFoam low Ma	#1
VSass Member VS Join Date: Nov 2012 Posts: 86 Rep Power: 14	Hey lads, i'm trying to simulate a flow of U=0.01m/s around a sphere (Re=183). I've already done this with icoFoam and now i'm trying to get the same results using rhoCentralFoam, but the problem do not seem to converge. I've read somewhere that this solver needs preconditioning in order to solve for low Ma speeds. Is that why i don't get a similar,converged solution like the one in icoFoam? Thanks

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July 3, 2015, 10:41		#2
chriss85 Senior Member Join Date: Oct 2013 Posts: 397 Rep Power: 19	Sorry for the late reply, just thought I might add something. Generally, density based solvers like rhoCentralFoam are not suited for very low Mach number flows, like you appear to have. It's better suited for transsonic/supersonic scenarios. For subsonic cases pressure based solvers are more reliable. However, I too would like to know up to which lower Mach value the rhoCentralFoam solver is deemed suitable.

July 5, 2015, 01:33		#3
AshwaniAssam Senior Member Ashwani Join Date: Sep 2013 Location: Hyderabad Posts: 154 Rep Power: 13	rhoCentralFoam being a density based solver can not be directly used for low mach number as mentioned by Chriss. The solver does not have preconditioning or other low-mach number technique. I am not sure much about the limit but it could be above M =0.3 . Also, You should not be even getting an accurate solution. Are you getting correct result?

July 6, 2015, 04:50		#4
chriss85 Senior Member Join Date: Oct 2013 Posts: 397 Rep Power: 19	Do you happen to have some literature regarding preconditioning techniques or other concepts for low Mach numbers in density based solvers? I'm solving a transient problem in which I can get quite different speeds and Mach numbers (large range of temperatures, and so I also get very different speeds of sounds). I'm not really sure which solver would be best for this. Right now I've based my code on sonicFoam, but sonicFoam is known to perform badly on transsonic/supersonic speeds compared to rhoCentralFoam.

July 6, 2015, 14:01		#5
AshwaniAssam Senior Member Ashwani Join Date: Sep 2013 Location: Hyderabad Posts: 154 Rep Power: 13	Did you tried sonicFoam for subsonic cases. It is a pressure-based alogo, it should be working fine. For Preconditioning you can see Blazek CFD book, or just google weiss preconditioning.

July 7, 2015, 04:59		#6
chriss85 Senior Member Join Date: Oct 2013 Posts: 397 Rep Power: 19	Yes I'm currently using a solver based on sonicFoam. I just want to make sure it's the optimal choice for me