Transition point extraction (k-kl transition model)
 

Hello OF users,

I have a simple question: is there a way to write out the transition location on a surface when computing with the k-kl transition model? I am running a calculation on an airfoil and would like to know the predicted transition point on the upper and lower surfaces. This is to be done after the computation is converged - anyone knows of a way to do this?

I have thought that you can look at the pressure distributions but that would be quite tedious as I have many cases and angles of attack. Any elegant alternatives are appreciated!

Thanks!

cf
 

The first thing I have to say is that there is not a single transition point. you can talk about a transition zone, but not a transition point, at least not for this model. Physically it makes sense, since transition does not happen instantly, it is a process.

You can see that zone by plotting the skin friction coefficient, it will increase once the transition starts until fully turbulent flow is achieved.

Also, there is a new transitional model in the market that all k-kl-omega users have to switch to.

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