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K-e Relizable in CFX

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Old   June 19, 2016, 16:36
Default K-e Relizable in CFX
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Aja
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Hi,

Is there K-e Realizable model in CFX?

There was this model in Fluent. I just see k-e scalable and RNG k-e in CFX...

I want to predict point of turbine stall by using K-e models. Which model is good in this case?

I am grateful that guide me in this case.

Thanks.
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Old   June 19, 2016, 20:15
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Glenn Horrocks
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CFX does not have the k-e realizable model. CFX has deliberately not put every available turbulence model in the software, the ones which are in there are chosen as they are widely used and are the best available for a significant class of flows. The k-e realizable model has not made the cut.

My recommendation for choice of turbulence model is: Use SST unless you know a good reason not to. I have not heard you mention a good reason why the SST model should not work in your case, so SST is my recommendation.
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Old   June 20, 2016, 02:59
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Quote:
Originally Posted by ghorrocks View Post
CFX does not have the k-e realizable model. CFX has deliberately not put every available turbulence model in the software, the ones which are in there are chosen as they are widely used and are the best available for a significant class of flows. The k-e realizable model has not made the cut.

My recommendation for choice of turbulence model is: Use SST unless you know a good reason not to. I have not heard you mention a good reason why the SST model should not work in your case, so SST is my recommendation.
Thanks for your reply.

Y+ is near 1 on the blade and i am sure that grid is not sensitive to this boundary layer resolution.

I should obtain the following result. this parameter is torque coefficient that is proportional to torque(T).

As you see above picture, stall happens about flow coefficient equal to When i decrease number node in node, stall happens in flow coefficient equal equal to 0.!!!! this is my reason because this happen creates wrong validation.


explanation about torque coefficient is as follows:

Horizontal axis is flow coefficient. Calculations are carried out at different values of flow coefficient/, where:

U*=v/U

The flow coefficient is varied by varying the axial velocity,v, while keeping the rotational speed constant.


more explanation:

Shear stress transport is K-w sst. Am i right?


Thanks

Last edited by aja1345; July 9, 2016 at 08:28.
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Old   June 20, 2016, 03:22
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What is deference between these two following models?

Last edited by aja1345; June 21, 2016 at 04:03.
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Old   June 20, 2016, 07:26
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Quote:
Shear stress transport is K-w sst. Am i right?
Yes.

Difference between SST and k-omega: SST uses k-e in the core of the flow and transitions to k-omega at the walls.

Your comment that changing node count in the inlet changes the result says you are not mesh insensitive. You probably need a finer mesh to resolve this properly. Note that there is more to mesh sensitivity than just y+. y+ is just the near wall resolution.
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