# Von Karman Vorticity

Is it possible with a BGK model to simulate a von karman vortex around a cylinder? Which parameters are the responsables for this phenomena?
Right now i´m ussing a pouiseuille flow with a Re=100 and a cero gradient output in a 400x51 grid, but nothing happens???

Thanks

Spartan

Yes it is! But you have to break the symmetry of your simulation. Try putting the center of your cylinder a bit off the middle of the channel (one cell upwards for example). This should do it.

But still nothing is happening, i broke the symetry, and i fixed Re=100 in the same way it´s done on the lbm code example cylinder, i set the umax of the pouiseuille flow at the inlet, with that i calculate the cinematic viscosity and omega.

Cuould it be a mistake in the unit conversion? I allready read the document posted and i think i´m doing the same as at the example, what i am doing wrong?!!!

Does the relationship between the cylinder´s diameter and the channel´s width special?

This is the only simulation that is missing in order to finish my undergraduate thesis, help me!!!

Spartan

do you use no-slip or periodicity on top/bottom boundaries (i guess no-slip is more favorable to unstable flow)? what bc do you use on inlet/outlet? zou/he?

At the Top/Bottom BC´s i´m using non-slip boundaries, and at the output i´m using zero gradient on rho and ux, and at the input BC´s with a poiseuille flow. All the BC´s are Zou and He.

Something weird happened. I doenload cylinder.m and fix my model with the exact parameters that Jonas used on his model, to try to understand what is happening with mine, but it reaches inestability. I don´t know why? The only way to keep it stable is to change the omega, but happens the same, the flux stabilizates after some time and the vorticity never appears!!!