CFX Solver Reynolds Number

haider760 · March 1, 2012, 00:34

Hello all,

I was simulating simple flow inside a pipe for seeing pressure drop and heat transfer during the flow. I found that Reynolds number that Cfx solver calculates is quite different from the theoretical Reynolds Number.

I went through different threads which states that because cfx uses length scale which is cube root of volume therefore we have this difference.

I have understanding that due to difference of Reynolds number physics of flow will change (i.e laminar flow will be in turbulence regime) and if i have to compare it with some correlation that are based on theoretical Reynolds number, then the comparison may not be appropriate.

I also defined theoretical Reynolds Number using additional variables, but i found that momentum equations are still solved using cfx solver calculated Reynolds Number.

I was wondering if there could be any way that i can define cfx solver reynolds number as the theoretical Reynolds number so that i can compare my results on an equal ground. Or should i ignore this difference in Reynolds Number and still compare my results?

Any help will be appreciated?

Thanks
Regards
Haider

ghorrocks · March 1, 2012, 18:01

You cannot change the Re number reported in the output file. It is just a guide as to what flow regime the flow is likely to be in, and it can be completely wrong. It is not used in the solver to set anything, it just triggers some warning messages (which can be ignored if not relevant). Just ignore it and use your own definition of Re number.

haider760 · March 4, 2012, 23:05

Thanks Gorrocks!

It really cleared many doubts!

March 1, 2012, 00:34	CFX Solver Reynolds Number	#1
haider760 New Member Haider Muhammad Join Date: Dec 2011 Posts: 5 Rep Power: 14	Hello all, I was simulating simple flow inside a pipe for seeing pressure drop and heat transfer during the flow. I found that Reynolds number that Cfx solver calculates is quite different from the theoretical Reynolds Number. I went through different threads which states that because cfx uses length scale which is cube root of volume therefore we have this difference. I have understanding that due to difference of Reynolds number physics of flow will change (i.e laminar flow will be in turbulence regime) and if i have to compare it with some correlation that are based on theoretical Reynolds number, then the comparison may not be appropriate. I also defined theoretical Reynolds Number using additional variables, but i found that momentum equations are still solved using cfx solver calculated Reynolds Number. I was wondering if there could be any way that i can define cfx solver reynolds number as the theoretical Reynolds number so that i can compare my results on an equal ground. Or should i ignore this difference in Reynolds Number and still compare my results? Any help will be appreciated? Thanks Regards Haider

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March 1, 2012, 18:01		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	You cannot change the Re number reported in the output file. It is just a guide as to what flow regime the flow is likely to be in, and it can be completely wrong. It is not used in the solver to set anything, it just triggers some warning messages (which can be ignored if not relevant). Just ignore it and use your own definition of Re number.

March 4, 2012, 23:05		#3
haider760 New Member Haider Muhammad Join Date: Dec 2011 Posts: 5 Rep Power: 14	Thanks Gorrocks! It really cleared many doubts!