Reynolds number in Source Term

kastarkas · July 17, 2018, 07:16

Hello everyone,
I came across a source term for gas transport with diffusion.
The source term consists of "Reynolds number" term. So while creating CEL's, apparently there is velocity in that. (i.e the "velocity" variable from variables list)
and we know CFX doesn't allow for "non scalar variables" (in this case, velocity) in source terms;
Since I had different cross sections in my flow path, I went that way.

So should I compute velocity based on my geometry and flow rate, may be at inlet and then use it ? Is this right, (coz I have diff cross sections) ?

Thanks for any suggestions or inputs in advance..

Opaque · July 17, 2018, 19:59

As far as I recall, the Reynolds number does not depend on velocity (velocity is a vector), but a characteristic speed (is a scalar)

It is not clear what you meant about source cannot depend on "non-scalar variables". If the source term is for a scalar equation, it cannot be a function of a vector. Perhaps a function of the magnitude of the vector, but not the vector itself.

kastarkas · July 18, 2018, 01:51

great. Thank you Opaque; my bad it was; slightly got confused with velocity and speed; magnitude of velocity worked.
Thanks again.

July 17, 2018, 07:16	Reynolds number in Source Term	#1
kastarkas Member kastarkas Join Date: Aug 2016 Posts: 45 Rep Power: 9	Hello everyone, I came across a source term for gas transport with diffusion. The source term consists of "Reynolds number" term. So while creating CEL's, apparently there is velocity in that. (i.e the "velocity" variable from variables list) and we know CFX doesn't allow for "non scalar variables" (in this case, velocity) in source terms; Since I had different cross sections in my flow path, I went that way. So should I compute velocity based on my geometry and flow rate, may be at inlet and then use it ? Is this right, (coz I have diff cross sections) ? Thanks for any suggestions or inputs in advance..

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July 17, 2018, 19:59		#2
Opaque Senior Member Join Date: Jun 2009 Posts: 1,804 Rep Power: 32	As far as I recall, the Reynolds number does not depend on velocity (velocity is a vector), but a characteristic speed (is a scalar) It is not clear what you meant about source cannot depend on "non-scalar variables". If the source term is for a scalar equation, it cannot be a function of a vector. Perhaps a function of the magnitude of the vector, but not the vector itself.

July 18, 2018, 01:51		#3
kastarkas Member kastarkas Join Date: Aug 2016 Posts: 45 Rep Power: 9	great. Thank you Opaque; my bad it was; slightly got confused with velocity and speed; magnitude of velocity worked. Thanks again.