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K-epsilon vs. k-omega turbulence modelling

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Old   January 6, 2012, 06:00
Default K-epsilon vs. k-omega turbulence modelling
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Hello,

I am currently working on a heat transfer model involving strong vortical cooling effects in the pressure based solver. To reduce computational expense, the turbulence models of choice are the realisable k-epsilon and SST k-omega two equation models, with the aim to fully resolve the boundary layer with a suitably defined fine mesh density.

These two models have returned sizeable numerical differences. I am trying to understand why this could be. Could anyone give any information regarding these turbulence models for this particular case?

Cheers

Tom
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Old   January 14, 2012, 00:45
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Lucky Tran
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The SST k-omega model reduces to a standard k-epsilon model away from walls.

Near walls, the SST k-omega uses the the omega formulation whereas the realizable k-epsilon uses the epsilon formulation.

The two models differ in their approach both near walls and away from walls.

The SST k-omega model is generally thought to be better near walls, but because it reduces to the standard k-epsilon model away from walls and not the realizable k-epsilon model, it also has weaknesses.

The two models are very different and it should be no surprise that significant differences in results can be obtained from each model (this should be considered the norm rather than unusual).
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Old   January 15, 2012, 13:38
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Thank you for your input.

You have alerted me to one point regarding the turbulence models I have used; that being the SST k-omega model which has a blending function to reduce the model to the standard k-epsilon model.

I overlooked this feature, and was expecting that the solutions provided would support the application of the SST k-omega model, given its suggested superiority in the near wall flow regions.

It would be good to gauge what turbulence models other users of Fluent have adopted to capture steady state heat transfer, particularly when flow characteristics such as separation, reattachment, and recirculation have a strong presence.
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Old   January 24, 2012, 07:13
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Hi,
I have used SST k-omega model, Realizable and RNG k-epsilon models for a similar problem involving heat transfer in a duct (internal flow) with a lot separation, reattachment and re-circulations at near-wall regions. Significant differences in wall temperatures are seen between the turbulence models.
Unfortunately very high temperatures are obtained with the usage of SST k-omega model compared to the k-epsilon models, which has resulted in bad-comparison with the results from the literature. This finding is contrary to other numerical simulation papers. The re-circulation size in case of SST k-omega model is also very different from the k-epsilon models.
y+ less than 1 was maintained for all the cases.

The reason for high temperatures with the usage of SST k-omega model evades me. Please let me know of your suggestions, as to what can be wrong.

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Avinash
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Old   February 6, 2013, 23:42
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Hi,
did you find the reason for the wrong behavior of the SST?
I recognized the same behavior when applying the SST in separated flows (although in OpenFoam) getting to high wall temperatures and a significant underestimation of the Nusselt number respectively.

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Pascal
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