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Old   March 16, 2007, 00:34
Default Discrete Vortex Method
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Sowmitra Singh
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I am trying to simulate the flow past a cylinder using discrete vortex (vortex blob) method. To evaluate the circulation strengths of blobs on the cylinder, I make the normal flow through the cylinder zero. I then make use of the no-slip condition to determine the strengths of blobs being shed from the cylinder surface. The problem is that the strengths of blobs being shed are less than those of the wall blobs by a factor of 1000. As a result, the flow does not seem to develop. What could be the reason?

A few typical values that I am using are : Flow velocity (U) = 1 m/s Reynolds number = 550 Blob radius = 0.34m (for a cylinder of radius 1m - i.e enough to ensure a good overlap between the blobs.)

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Old   March 16, 2007, 15:59
Default Re: Discrete Vortex Method
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Adrin Gharakhani
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First, your blob radius is huge. Rule of thumb: the blob radius should be about 1.5~2 times the nominal interparticle spacing (the "grid size").

Second, you haven't mentioned how you're going from the no-slip step to the blob circulation step. But, following the no-flux BC, you get a slip velocity at the wall. Multiply that velocity by the panel length to get the panel circulation (the panels are the little segments that you use to define your circlular geometry). The simplest strategy is now to give off the panel circulation to the particle directly above it at a distance that represents the center of the stokes layer (to represent diffusion from the wall to the flow). So, now, the wall has zero circulation and the blob has circulation equal to that of the wall

Adrin
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