# Dimensionless numbers

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 September 5, 2007, 09:25 Dimensionless numbers #1 kuba Guest   Posts: n/a Hi, I have to compare to different flow patterns (gas convection) and as a first shot I chose dimentionless numers like Reynolds number, Grashof number, Rayleigh number. Could anyone help me and tell me how/what should I do in Fluent to get these data or some other ideas to compare two different geometries with different flows! Thank you in advance! Brgds, kuba

 September 5, 2007, 14:49 Re: Dimensionless numbers #2 V. Kumar Guest   Posts: n/a do not fully understand your requirement. I guess you want to set particular values of Re, Gr and Ra for your simulations. There are two ways for this: 1) compute everything in dimensionless form. That is transform your equations so that the coefficients of your governing equations are transformed to dimensionless numbers. Then simply compare the dimensionless equations with the equation in dimensional form. E.g. viscosity will be 1/Re thermal conductivity will be 1/Re Pr, density = 1, Delta T = 1, gravity = Gr/Re^2 and so on. 2) Another way is to fix dimensionless numbers and some properties and calcualte back your bounadry conditions and flow velocity and remaining properties from the definition of the dimensionless numbers. I hope this will help.

 September 6, 2007, 04:48 Re: Dimensionless numbers #3 kuba Guest   Posts: n/a Hi, Thank you for the answer but I thought about calculating these numbers for 2 different systems and then compare and draw some conclusions (what are the differences between them). But how to calculate these numbers in Fluent? Brgds, kuba