# turbulent flow....

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 November 17, 1998, 21:49 turbulent flow.... #1 Daejin,Kang Guest   Posts: n/a When using 'the k-¥å model', I think, I had to set the quantity of the turbulent kinetic energy, k, turbulent kinetic dissipation rate, e (or characteric length, l). We use the code of "CFD-ACE". How to set the k, e, l ......???? Ah, what is the eddy viscosity......and that quantity ???

 November 18, 1998, 16:06 Re: turbulent flow.... #2 John C. Chien Guest   Posts: n/a When the flow becomes turbulent, no one knows how to solve it. Once upon a time, there was a smart person who lived in a far away land . One day, he invented a set of time-averaged equations from the Navier-Stokes equations, and claimed that this set of equations can give you the answers of the turbulent flow. Inside this set of equations, there are unknown variables called Reynolds Stresses terms, which must be modelled and calculated before you can find the answers to the equations. In the last thirty years, researchers have been related these terms to eddy viscosity and velocity gradients. And the eddy viscosity also was further related to TKE ( turbulence kinetic energy) and TKE-dissipation. To find the answers to TKE and TKE-dissipation, you now have to solve a new set of equations , one for TKE and the other for TKE-dissipation. To go from here, a good book on turbulence modelling would be a better place to start. ( TKE-dissipation contains the length scale information of the turbulence model. A length scale is just a adjustable constant which can change from place to place in the turbulent flow. You can do whatever you like as long as you can get good results. A really good idea.)

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