CFX Error - Reynolds number out of range

saisanthoshm88 · May 10, 2012, 08:58

I was trying to run a case in and I encountered the following error:

The Reynolds number is outside of the range expected based on the Option selected for the TURBULENCE MODEL

Please look into the attachment for more info. on this error

I switched into the Laminar regime later and the problem is then resolved.

Could some one please let me know how to figure out the Reynolds number even before starting the run ( The domain geometry may not be simple in all the cases).

Lance · May 10, 2012, 09:54

It's a warning, not an error.

http://www.cfd-online.com/Forums/cfx...ide-range.html

saisanthoshm88 · May 11, 2012, 01:42

Could some one please explain how to know the Reynolds number for a complex geometry before starting the run. I mean if we are clear about the flow regime beforehand then it would help to plan the meshing.

ghorrocks · May 11, 2012, 07:04

Remember that in this case Reynolds number is simply used to determine which regime you are in. So it does not need to be calculated exactly. So just use any length, velocity and fluid property values which are representative of your geometry. If you know the transitional Reynolds number for the geometry you then know if it is laminar or turbulent and can choose a turbulence model appropriately.

Likewise for getting an appropriate y+ up-front, estimate the mesh requirements by what you expect the flow to do. The documentation has a guide of how to estimate y+.

But do not be surprised if this initial guess is wrong and requires some adjustment. It is an estimate, after all.

May 11, 2012, 01:42		#3
saisanthoshm88 Senior Member --------- Join Date: Oct 2010 Posts: 303 Rep Power: 17	Could some one please explain how to know the Reynolds number for a complex geometry before starting the run. I mean if we are clear about the flow regime beforehand then it would help to plan the meshing. __________________ Best regards, Santhosh.

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May 10, 2012, 09:54		#2
Lance Senior Member Lance Join Date: Mar 2009 Posts: 669 Rep Power: 22	It's a warning, not an error. http://www.cfd-online.com/Forums/cfx...ide-range.html

May 11, 2012, 07:04		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Remember that in this case Reynolds number is simply used to determine which regime you are in. So it does not need to be calculated exactly. So just use any length, velocity and fluid property values which are representative of your geometry. If you know the transitional Reynolds number for the geometry you then know if it is laminar or turbulent and can choose a turbulence model appropriately. Likewise for getting an appropriate y+ up-front, estimate the mesh requirements by what you expect the flow to do. The documentation has a guide of how to estimate y+. But do not be surprised if this initial guess is wrong and requires some adjustment. It is an estimate, after all.