Calculating Wall Shear Stress & Skin Friction Coefficient

[CFD Engineer]

Hello all,
I am simulating flow over an airfoil (2D & 3D) and finding a way to get the values of wall shear stress and skin friction coefficient on the walls of my airfoil. I have 2 separate walls (one upper and one lower wall of airfoil) and need to compute these two variables on them separately. Since I am new to Nek5000, can any body here guide me how I could do that and obtain the plots of these 2 things in nek5000.
Will really appreciate it.

Thanks. 

[stek...@gmail.com]

Hi, I suggest you look at the turbChannel example and go from there.

Basically I'd try to do it like this:

- assign an object index to each surface of interest, say the upper wall is object 1, the lower wall is object 2

- call torque_calc in userchk

- now you can access drag-force for each object via:

dragx(objectindex)

dragy(objectindex)

dragz(objectindex)

- now calculate your coefficients; for example divide the wall-tangential component of the drag by the surface area to get the average wall shear. There are pre-calculated arrays with element surface areas and surface normals that help you do this.

There's also the KTH statistics toolbox that might be of help.

hope that helps!