Newbie: why use stream function instead of solving for x and y flow components?

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 January 2, 2012, 13:07 #2 Senior Member     Paolo Lampitella Join Date: Mar 2009 Location: Italy Posts: 518 Blog Entries: 14 Rep Power: 17 My knowledge about the streamfunction-vorticity (SV) method is at textbook-basic programming level but i think it's fair to say: - The main advantage of the SV method is in 2D computations, where only 2 equations need to be solved (psi and omega) versus the 3 required by a classical approach (u, v and p). - The continuity equation is satisfied by construction due to the use of the streamfunction (however, there is probably more under the hood) - There are probably also people using it for 3D computations. I guess, because of the continuity equation advantage For what concerns the trajectories, if the flow is steady and 2D they coincide with the streamlines so they are easily obtained as contours of the streamfunction

 January 3, 2012, 09:22 #4 Senior Member   Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 194 Rep Power: 8 you don't have to worry about the pressure is the main reason. After solving for the velocities you can come back and get the pressure if you need it.

 January 3, 2012, 10:31 #5 New Member   Join Date: Jan 2010 Posts: 28 Rep Power: 7 Hi everyone: Thanks a lot for all your help!! Really appreciate it. Well, it sounds like there wouldn't be any DISADVANTAGE to using the primitive variables method instead of the vorticity-streamfunctions method. It doesn't sound like there's any information I'd miss if I used primitive variables (this worried me). Also, I agree with otd that it might be best to use the primitive variables method because I'm not confident I understand what is going on under the hood of the vorticity method (e.g., the exact assumptions that are incorporated). My chemistry is quite complex--it would lead to density and viscosity and pressure variations. So there could be simplifying assumptions for using the vorticity-streamfunction method that might get me into trouble. mettler, do you mean that when using the streamfunction method, we don't solve for P, but we can get it once we have the velocity? Again, thanks a lot for your patience. It is nice to be able to get some knowledgeable opinions before diving right in and perhaps starting off on the wrong foot!

 January 3, 2012, 10:55 #6 Senior Member   Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 194 Rep Power: 8 yes, when transforming the equations into the stream function - vorticity equations the pressure term drops out. I highly recommend going thru the math to get to the stream function-vorticity equations. It is not very difficult, but it is rather time consuming. It is just a lot of substitution. But, it will help out in the long run.

 Tags stream-function, streamfunction, streamline, vorticity

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