# BCs for stream function/vorticity

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 October 12, 2005, 15:44 BCs for stream function/vorticity #1 Andrew Hayes Guest   Posts: n/a I am trying to move my program from the cavity flow to flow between two plates using the stream function/vorticity equations, and I am having trouble with the exit. For the entrance I assumed a uniform flow field. This gave Uy=0 and Ux=const, which led to vorticity=0 at the entrance, which makes sense. For the exit, I am also getting zero if I assume fully developed flow. Is that correct? thanks

 October 12, 2005, 19:35 Re: BCs for stream function/vorticity #2 Mani Guest   Posts: n/a Look at the definition of vorticity, consider a non-uniform (fully developed) velocity profile, and you will realize that vorticity cannot be zero in fully developed flow between two plates.

 October 12, 2005, 20:26 Re: BCs for stream function/vorticity #3 Andrew Mettler Hayes Guest   Posts: n/a I know it is not zero between the plates. I am trying to get the BCs at the entrance and exit. I have the BCs for the top and bottom. thanks for your help

 October 13, 2005, 13:11 Re: BCs for stream function/vorticity #4 Mani Guest   Posts: n/a Maybe I misunderstood your question. Just to make sure: The vorticity is not zero anywhere in a fully developed flow. This means that you cannot use zero vorticity at the exit boundary condition. If you know the velocity profile at the exit, you can then obtain the appropriate (non-zero) vorticity and apply that as a boundary condition. Does this answer your question?

 October 13, 2005, 14:10 Re: BCs for stream function/vorticity #5 Andrew Hayes Guest   Posts: n/a thanks, that helps out. I am having most of my trouble at the exit. So, I can use the curl of the velocity vector to find the vorticity at the exit and set that as the boundary condition? I think I can make that work in my program. thanks

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