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 ChrisPro April 5, 2012 12:36

kkl-omega coefficients

Hey All!

I'm doing 3D wing analysis using the kkl-omega turbulence model.
Does someone of you know how to calculate
kl
kt
omega
nut
and nuTilda ?

Christian

 wiedangel June 6, 2012 04:23

Hi ChrisPro,

you calculate omega and k like you do for the komegaSST or komega model. The other kl, kt you can get the values by looking at the paper:
"A three equation Eddy-viscosity model for Reynolds-Averaged-Navier-Stokes simulations of transitional flow". Journal of Fluids Engineering 2008.
Good luck.

 ChrisPro June 6, 2012 05:29

Hey!

you can leave away k

kt is calculated like k in the other turbulence models:
T*u_inf = sqrt(2/3*kt) / U_inf

in freestream one can set kl to 0

nut = Cmü,std * kt/omega

omega is the same as in the kOmegaSST model

Cmü,std = 0.09

I discovered that you can leave out nuTilda as well. The results are the same, but the timesteps it takes to get the desired residual is a bit higher!

greets
Christian

 wiedangel June 6, 2012 05:31

You are welcome ChrisPro. I am also working with kklomega, but my problem is the y+ = 1 condition which is not easy to satisfy while keeping the grid size manageable.

 ChrisPro June 6, 2012 14:53

that's true!

at the moment I simulate a case which runs since yesterday morning on a 24core machine... (and now its 8.53pm in my time zone :) )

What experienced have you made with the calculated Cl and Cd values?

With y+ = 6 I also got good residuals ( < e-06 ) but the values for Cl and Cd where much lower than expected.

greets

 wiedangel June 7, 2012 04:03

Hi ChrisPro,

for the moment I have no results yet, just began the struggle with the mesh to make it y+ conform without ending up with trillions of elements :o. I will share my findings when I have some data. I am also considering DES as it is less demanding meshwise.

 kiddmax February 13, 2014 05:26

Hi ChrisPro

I am also interested in kklomega transition model. I have validated it for 2D airfoil, but not successful with 3D complex wing, it also have convergence problem. Would you please show your fvScheme and BC setting? and what about your solver? steady solver or transient solver?

Thank you!

Best regards,
Ye

 be_inspired June 16, 2014 11:37

I really hope someone could help me.
I am trying to simulate a simple 2D airfoil with kkl omega model.
My bcs are for wall are:
kt=0
kl=0

My setting are:
U=50m/s
TI=1%
turbulent length scale=0.01m
So:
kt=0.375
omega=61.23
nut=0.00055

I have use a very low relaxation factors, but I do not obtain good results.
My mesh, runned with SA (nutSpaldingWallFunction) runs correctly:
maximum yplus=2 ( just at TE region). Minimum=0.1. Average = 0.3

 Ranjan August 18, 2015 15:30

Hi Kidmax

I am trying to get some airfoil results using kkl-omega model with PimpleFoam. May I ask how your results looked like ? I am currently getting very high cl & cd values.

 malv83 June 17, 2016 15:09

new model

After 8 years, there is a new version (or new model) of the k-kl-omega model.

There are a few problems with the k-kl-omega model in the farfield. One of them is the growth of Laminar Kinetic energy when separation occurs. Lopez and Walters have a paper (have not been published yet) correcting this issue:

Maurin Lopez. D. K. Walters. “A recommended correction to the k-kl-omega transition sensitive eddy-viscosity model”. Journal of Fluid Engineering.

This correction has to be made to the 2008 k-kl-omega model from now on.

Now, Lopez and Walters also developed a new transitional model (k-omega-v2) as an alternative to the k-kl-omega one. This new model has more capabilities (it is more reliable) than the k-kl-omega model, especially in the farfield computations. Fortunately the paper for this new model is already publish.

Maurin Lopez. D. K. Walters. “Prediction of transitional and fully turbulent free shear flows using an alternative to the laminar kinetic energy approach”. Journal of Turbulence, Vol 17, Iss. 3, 2016.

If you see the papers, you will immediately see how the k-kl-omega model is not good for free shear flows, and how the new model corrects all those issues. From now on, k-kl-omega users have to start using the new k-omega-v2 model.

Hope this helps

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