# Question...Turbulence Intensity & Viscosity ratio

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 October 6, 2005, 03:40 Question...Turbulence Intensity & Viscosity ratio #1 Jay Guest   Posts: n/a Hi Is there somebody who could explain the meaning of "Turbulence Intensity, Back flow Turbulcen Intensity and Turbulence Viscosity Ratio"? I do not know why those are 5% or 10%. Please give me a tip. Thanks

 October 6, 2005, 04:41 Re: Question...Turbulence Intensity & Viscosity ra #2 RoM Guest   Posts: n/a Turbulence intensity is defined as the ratio of the root-mean-square of the velocity fluctuation (u') and the mean flow velocity (u_avg). It can be estimated in terms of Re using equation 7.2-1 from the users guide. A Re number of 5e4 is equal to a turbulence intensity of 4% (according to 7.2-1). Turbulent viscosity ratio is define as the ratio of the tubulent viscosity (calculated by your tubulence model) and the laminar viscosity (from the material panel). For most fully turbulent flows it will range from 1000 to 1e4. Backflow parameters are taken by fluent if any backflow occurs during the iteration, otherwise they are not used. A good guess of these parameters will help your solution to run stable if backflow occurs, a (very) bad guess can cause divergence. Read users guide chapter 7.2.2 "Determening Turbulence Parameters" for more information. RoM hossein65 and Anna Tian like this.

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