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low-Reynolds-number k - ε turbulent model

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Old   February 28, 2009, 12:52
Default low-Reynolds-number k - ε turbulent model
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Dear all,

Can any one shed some light on the low-Reynolds-number k - ε turbulent models provided by Fluent ?

Can I use it in VOF model ?

Hope to get some reply

Best wishes.

D.
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Old   March 3, 2009, 04:45
Default Re: low-Reynolds-number k - ε turbulent model
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Any reason why you need a low Re turb model for VOF?
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Old   March 3, 2009, 04:52
Default Re: low-Reynolds-number k - ε turbulent model
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At certain places of my flow, I will have turbulent, yet low Reynolds flows..since my target is to model in VOF, so i intend to use the same in VOF. why ? Is there anything wrong in not using it ? pls give your suggestions. Thanks.
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Old   March 3, 2009, 04:59
Default Re: low-Reynolds-number k - ε turbulent model
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Low-Re Turb model looks at resolving the viscous sublayer of the boundary layer for bounded flows. The VOF model looks at multphase flow cases, I would think that resolving the viscous sublayer is the least of your worries. The standard k-e model should give reasonable turb values for any VOF case.

Hope that helps.
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Old   March 3, 2009, 05:21
Default Re: low-Reynolds-number k - ε turbulent model
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ok, i understand your point. let me write in more detail: i have a liquid in which gas bubbles are going up..now for this i am using VOF approach. the problem is i am calculating the shear stress at a point on the wall, where this bubble will flow past. the shear is due to the liquid squezzing down past the bubble, along the wall, as the bubble goes up. now, the shear computed doesn't match the exptl. results. i was thinking if i have modeled the small part ie. the part which undergoes the shear; so i was thinkign of low Re-Turb model approach here. what do you suggest here ? why do you think it is not matching with the exptlly observed shear ? thanks and kind regards.

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Old   March 3, 2009, 05:34
Default Re: low-Reynolds-number k - ε turbulent model
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I would think that the mesh might play a big role in this, have you done a mesh independent study? Also, what about your surface tension coefficient? Have you ensured that you're using correct values? Are you doing 2D or 3D? If 2D, this might be a source of error as well.

Yes, turbulence might in fact be a source of error, and thus the low-Re might be useful. Bear in mind that your mesh size needs to be in the orde of Y+=1, and have around 15 layers of mesh in the boundary layer. You can use the realizable k-e with the non-equilibrium wall functions, or you can use the k-w, which is inherently a low-Re turb model.

Hope that helps.
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Old   March 3, 2009, 05:37
Default Re: low-Reynolds-number k - ε turbulent model
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thank you very much, i am going to study your suggestions and will get back to you. thanks a lot.
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Old   June 16, 2009, 09:09
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Dear All,

I am trying to compare some shear stress experiments with CFD using the RNG k-e model, but my CFD results are under- and overpredicted compared to experimental data in certain zones so I wonder how you solve your problem (turbulence model, mesh, etc).

Thanks for the help
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