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Old   June 2, 2005, 18:43
Default k-e turbulence
  #1
hung
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Hi everyone!

Now I'm modeling a turbulence flow over the spheroid by Fluent, and I used K-epsilon model. But my result ( Cf, Cp....) are quite difference to the results in the paper.

I used the K-epsilon, but I'm not sure about the coefficients in this model, for example k, epsilon....

Somebody can recommand to me, how to simulate it to get a better result. Thanks a lot!

pah
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Old   June 2, 2005, 21:02
Default Re: k-e turbulence
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zxaar
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read the discussion "Which do you prefer? 6.1 or6.2?" on this page, there what ever i have said is applicable to the case you are talking about.
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Old   June 3, 2005, 01:09
Default Re: k-e turbulence
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hung
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Thanks for your reply!

I'm doing with the Prolate spheroid 6:1 and it has angle of attach 10, 20 deg at Re=4.2*1e6. And I did with k=0.1, epsilon=0.1. But the result so bad.

Somebody, Plz recommand to me the way to simulate it. Thanks one more!

PAH
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Old   June 3, 2005, 02:14
Default Re: k-e turbulence
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zxaar
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did you read the discussion i suggested to read,
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Old   June 3, 2005, 02:46
Default Re: k-e turbulence
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hung
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Hi zxaar!

I did, that's great and detail guiding. But my problem now is Turbulence models only. Because I want to complete turbulence model at the Steaty state case first, if it's true then I go to unsteady case.

Therefore, I'm considering the Tur coefficients. Could you recommand some ideas about it to me!

Thanks a lot!

PAH

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Old   June 3, 2005, 03:25
Default Re: k-e turbulence
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zxaar
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see if you have to stik to steady state calculations of k-e type, the best results you get with k-e realisable, and if u can have yplus near to 1, use enhanced wall functions, but with k-e type models you will need prism mesh near to walls of your body. and using yplus near to 1 is your best bet.

i suppose RSM should also give good results but i haven't tried it yet. note using prism near to walls gives best pressure coefficient predictions.
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Old   June 3, 2005, 03:46
Default Re: k-e turbulence
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hung
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Thanks for your recommand!

I use the k-e model and my grid on the wall is hex, because the hybrid grid is used in my model in some blocks.

And then, at the Models is set up with k-e realisable. But in the Inlet BC, we need to set up K, epsilon. In here, I'm trouble. I just set them as I mentioned.

Thanks !

PAH
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Old   June 3, 2005, 03:52
Default Re: k-e turbulence
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zxaar
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use intensity and lengh scale instead, read what manual has to say about it, in the boundary conditions part, then judge what you want to set,
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Old   June 3, 2005, 05:38
Default Re: k-e turbulence
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hung
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I want to set the dimensionless model of flow over the spheroid, and then I use the Velocity inler is U=1 with the long axe a=1.

Do you have some ideas about dimensionless in Fluent?

Thanks a lot, Zxaaz!

PAH
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Old   June 3, 2005, 06:34
Default Re: k-e turbulence
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zxaar
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nope i never tried that
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