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-   -   Use custmer defined function to calculate Re (http://www.cfd-online.com/Forums/fluent/39369-use-custmer-defined-function-calculate-re.html)

peter January 24, 2006 07:14

Use custmer defined function to calculate Re
 
I used a pressure inlet and pressure outlet bc for inlet and outlet respectively in a 2d case, i want to use the simulated velocity at inlet to calculate the Reynolds number, so i use coustmer defined function panel, and I chose "select operand field function from (VELOCITY->Velocity Magnitude )*(GRID->Y coordinates)/(PROPERTIES->Molecular viscosity), this means U*D(pipe width)/viscosity, but the results seems not right. any one who konw how to do this? or anyother easier method? thanks you very much

Mario January 24, 2006 09:39

Re: Use custmer defined function to calculate Re
 
Try the following definition: Re = U*D*density/viscosity

I think you have mixed up dynamic and kinematic viscosity. In your equation "viscosity" represents the kinematic viscosity but Fluent provides the dynamic viscosity.

kinematic visc = dynamic visc / density


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