Why in invicid model it has vortex

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 March 16, 2012, 04:45 Why in invicid model it has vortex #1 Member   Yolk Join Date: Nov 2011 Posts: 38 Rep Power: 6 hi, when I do a invicid model in which there are pressure jump(fan model), it generate vortex on the wall. Can you tell me the reason?Thank you!

 March 16, 2012, 05:18 #2 Senior Member     Amir Join Date: May 2009 Location: Montreal, QC Posts: 739 Blog Entries: 1 Rep Power: 15 Hi, Your assumption is not right. Each inviscid flow is not necessarily irrotational!!! (e.g. rigid body rotation). Nevertheless, ensure that you've achieved converged solution. Bests, __________________ Amir

March 16, 2012, 05:35
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Yolk
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Quote:
 Originally Posted by Amir Hi, Your assumption is not right. Each inviscid flow is not necessarily irrotational!!! (e.g. rigid body rotation). Nevertheless, ensure that you've achieved converged solution. Bests,
Hi Amir,
The defenition of vorticity in my thread is the curl of velocity. If it is invicid,du/dy,du/dz,dv/dx ... are all zero, so the curl of velocity is naught. Please comment.

March 16, 2012, 05:50
#4
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Amir
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Location: Montreal, QC
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Quote:
 Originally Posted by Yannian Hi Amir, The defenition of vorticity in my thread is the curl of velocity. If it is invicid,du/dy,du/dz,dv/dx ... are all zero, so the curl of velocity is naught. Please comment.
No!
The definition of inviscid flow is that the diffusion term of momentum equation can be neglected. As I said, in some cases like rigid body rotation this condition is satisfied but obviously the vorticity is not zero! i.e. :
Any irrotational flow is inviscid but not all the inviscid flows are irrotational.
I just wanted to clear this physical point for you but as a numerical point of view, when you use the inviscid model, you've ignored the elliptic term of momentum equation and it may cause some instabilities; consequently, you need more iterations for convergence. But as a tip, you can solve your case with full navier stokes equation and then use the converged results as your initial guess for inviscid flow. (This procedure is not common but can be used just for damping instabilities)

Bests,
__________________
Amir

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