turbulent model kepsilon
hi,
i am trying to look at the flow of air around a rectangle (length 7m and width 2.5m) (in turbulent regime). the inlet velocity is 16.66m/s. i solved in 2nd order implicit segregated. i have tried 3 different models of turbulent regime in order to compare them: kepsilon standard, Kepsilon realisable and Kepsilon RNG. i did focus my study on the recirculation zone generated after the rectangle and the drag coefficient. the results i have are quite disturbing: length of recirculation zone: kespilon standard: 4.44m kepsilon realisable: 4.36m kepsilon RNG: 7.59m drag coefficient kespilon standard: 2.3811 kepsilon realisable: 2.2554m kepsilon RNG: 2.5053m my problem is that i dont understand why the length of the recirculation zone is that big for the case of the kepsilon RNG. it is almost the double of the length for the realisable or the standard. if someone has an explanation that would be nice! thanks 
Re: turbulent model kepsilon
Hi, It depends on which model you are using. You have to select apporpriate model for your geometry from the literature available. Each model will treats the NS equations in different way. So, you should be careful before selecting the Turbulence model.

Re: turbulent model kepsilon
Hi there,
I am doing something pretty similar right now. You can look up a paper by Yao, Savill and Sandham (in Flow, Turbulence and Combustion 68, 2002); they compare DNS and RANS for the truncated trailing edge flow. RANS always gave approximatelly half the recirculation region. This might suggest that the RNG variant is actually closer to the truth. What is more peculiar is that the RNG and the realizable model do not agree well, but instead the realizable agrees with the standard. The solution will also depend on the wall functions used. Are you using the same wall functions in all 3 runs? Are the mesh densities the same? Also since you are using essentially variants of the same model, try using the SA model or the komega model and compare with that as well. Good luck! 
Re: turbulent model kepsilon

Re: turbulent model kepsilon

kepsilon method
Hi Im Surena Norouzi. Im from iran. Im a fluid mechanic engineering. I try to solve internal flow in a gas turbine blade. I must to use the KEpsilon Method to simulate flow. I use finite difference method to solve Navier Stocks equations. But i have not discreat form of KEpsilon equation in staggered mesh. please help me. regards

Re: kepsilon method
hello,
My project is also regarding internal flows of a turbine blade. I am trying to find the internal heat transfer coefficints and trying to cool the blade by means of impingement and film cooling. I am dealing with totally conjugat heat transfer. Can you please tell me on what model should i select and what boundary conditions should i apply. You please tell me as to what journals should i refer to or send some if you have already any. thanks Ravi 
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