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What viscous/turbulence model?

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Old   November 11, 2007, 12:34
Default What viscous/turbulence model?
  #1
DrBorque
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Hi,

I am new to CFD packages and there is one major thing that i don't understand with the CFD package ANSYS FLUENT. I am attempting to examine the flow around a human powered vehicle, which, for all intents and purposes, is a short and narrow car. The Reynolds number peaks at around 4.5x10^6 so it is fairly obvious that laminar and inviscid viscous models should not be used. I understand that k-epsilon is perhaps the best model to use as it is generally fairly easy going and can be used for almost anything (or so i've been told), but are there any other models that would do a better job? Computer time is not an issue. I'm not sure how to set the boundary conditions either, do i use k and epsilon, intensity and length scale (and what values for intensity and length), intensity and viscosity ratio, or hydraulic diameter (diameter being the width of the control volume i suppose)? I am also assuming that everything should be set to second order as this will increase accuracy, is this correct? Will using second order result in no convergence? I stress again that this is external flow only, there are no air intakes/vents on an HPV. Any help (or references to internet websites and books) you have to offer would be greatly appreciated.

Thanks in advance,

DrBorque
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Old   November 11, 2007, 23:10
Default Re: What viscous/turbulence model?
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Chandra Manik
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Dear DrBorque I would like to share you about your message, please also other correct me if i wrong.

1. Model and general feature You have to see your model, what model you want to generate. There are 2 typical model of feature in Fluent, 2D and 3D. And what typical condition in your model, is there any heat sources, or etc based on your model condition

2. Meshing I believe your meshing already finished and well in boundary condition, skewness, for boundary condition you can cange it anytime in Fluent.

3. Flow physic next you need to recognize your flow physic, first what is the domain, air water of ect?. If the water of any fluid pass from surface (in case 3D) you have to calculate Reynold number this important to recignize the formulation (laminar, or turbulence), if you want to see the effect of eddy current, please use LES (large Eddy simulation as an option of solver).

Dear, what i share here is very small part, better way you can adopt all condition well please refer to Fluent and Gambit User Guide, i prefer you can learn on Sample that they provide and also Validation formulation, they make it very well.

Regards

Chandra Manik

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