# How does Fluent RANS model work?

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 February 18, 2009, 21:50 How does Fluent RANS model work? #1 Tang Jingwei Guest   Posts: n/a I have a very basic question here. Am i right that Fluent only run on RANS and LES models? Why is it that the user does not need to input any temporal discretization when he uses a RANS viscous model, say K-epsilon? Is it because RANS model take the average of the different flow components at steady state? If so, am i right that one can only use LES to visualise unsteady flows?

 February 18, 2009, 21:57 Re: How does Fluent RANS model work? #2 Carlos Guest   Posts: n/a Hi, You are right, RANS is time averaged so not really suitable for time-dependent problems. LES is the best in Fluent for this but you need ultra fine grids for complex 3D problems. A compromise is to use DES or you can use URANS which is unsteady-RANS. This somehow uses RANS as unsteady and I think you can do this in the unsteady solver but I have only used RANS to date so not sure how it works. Carlos.

 February 18, 2009, 22:00 Re: How does Fluent RANS model work? #3 Tang Jingwei Guest   Posts: n/a Thanks for the reply! How do i use URANS?

 February 18, 2009, 22:09 Re: How does Fluent RANS model work? #4 Carlos Guest   Posts: n/a Not sure, think you select RANS model as normal then switch the solver from steady to unsteady. Thats all I know. Carlos.

 February 18, 2009, 22:10 Re: How does Fluent RANS model work? #5 Tang Jingwei Guest   Posts: n/a I get it! Thanks dude

 February 18, 2009, 22:21 Re: How does Fluent RANS model work? #6 Carlos Guest   Posts: n/a No problem, good luck....

 August 22, 2009, 15:08 RNG k-epsilon model #7 New Member   Ganesan Join Date: Aug 2009 Posts: 1 Rep Power: 0 hai, is this possible the molar concentration value is similar to laminar flow in unsteady flow? and is this needed to run turbulent model before to run LES model?

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