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-   -   Velocity inlet K and Epsilon (http://www.cfd-online.com/Forums/fluent/28572-velocity-inlet-k-epsilon.html)

Daniel Bruno June 3, 2001 16:57

Velocity inlet K and Epsilon
 
Hello all,

What values should be good for K and epsilon at a velocity inlet boundary condition for turbulent airflow around airfoils ?

Thanks,

Daniel Bruno

Chetan Kadakia June 7, 2001 22:39

Re: Velocity inlet K and Epsilon
 
I'm not sure if you have given enough info for one to say what are reasonable values of k and epsilon. k, being the kinetic turbulent energy equals u'u'/2. And turbulent intensity is u'/u(ave). And for freestream oncoming velocity of this type the intensity I believe is 5% to 10%. Maybe you can set the intensity or calculate k from the information I have just given

Can you tell us the parameters of the flow? Is it in the sky, or are you replicating a wind tunnel? Why do you choose a velocity inlet and not a pressure inlet?

Let me know if this helps, and if I am able to help any further.

-Chetan K.


Daniel Bruno June 10, 2001 20:42

Re: Velocity inlet K and Epsilon
 
Hi Chetan,

It is a numerical simulation of a wind tunnel flow. Is there something wrong with the velocity inlet ? I just used it because i know the free stream wind tunnel velocity (ok, with Vinf I can obtain the associated dynamic pressure). Is there some to enter 10 m/s or 61,25 Pa ?

Thanks,

Daniel Bruno

Chetan Kadakia June 11, 2001 17:24

Re: Velocity inlet K and Epsilon
 
Unless you are neglecting compressibility, you should use the pressure inlet condition (and probably also use a pressure outlet too).

Daniel Bruno June 16, 2001 18:54

Re: Velocity inlet K and Epsilon
 
It's a subsonic aiflow around an airfoil.

Chetan Kadakia June 17, 2001 01:47

Re: Velocity inlet K and Epsilon
 
See if the use of pressure b.c.'s make a difference. I forget what the reasoning behind that is. Also tell me, when using the velocity condition do use constant density or ideal gas?

For turbulence intensities in a wind tunnel, I've been told 5 to 10% is reasonable. i think you should conduct a thorough literature search for values of I, k, and eps. If you find empirical data on this before i do, then please tell us where you found it.


John C. Chien June 17, 2001 02:51

Re: Velocity inlet K and Epsilon
 
(1). The free stream turbulence level can have some effect on the boundary layer on the airfoil. (2). But in your case, you can set it to some numbers first. Obtain the converged solution, then change the free stream turbulence again to see how it affect your results. (3). The effect might be small.(depends on your interest in the airfoil boundary layer calculation). (4). It is always a good idea to match your conditions to the test conditions, if possible.


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