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-   -   Calculation of Vorticity (https://www.cfd-online.com/Forums/main/77984-calculation-vorticity.html)

 mortain July 8, 2010 18:49

Calculation of Vorticity

Hello,

I am using fortran for simulating the fluid flow not based on Navier Stokes but on lattice Boltzmann method!

I would like to evaluate the vorticity, given the velocity vectors.

The vorticity is, for the x direction, equal to:

http://www.cfd-online.com/Forums/vbL...55ccd28d-1.gif_x=(u_z(x,y+1,z)-u_z(x,y,z))-(u_z(x,y,z+1)-u_z(x,y,z))
since http://www.cfd-online.com/Forums/vbL...9222c03b-1.gifu/http://www.cfd-online.com/Forums/vbL...9222c03b-1.gifx=lim(http://www.cfd-online.com/Forums/vbL...168b0fff-1.gifx-->0)[u(x+http://www.cfd-online.com/Forums/vbL...168b0fff-1.gifx)-u(x)]/http://www.cfd-online.com/Forums/vbL...168b0fff-1.gifx hence I have to take the value of the next lattice minus the value at the lattice divided by one, which is the http://www.cfd-online.com/Forums/vbL...168b0fff-1.gifx.

Apparently tihs doesn't give the expected result in terms of vorticity. I was reading something here: http://folk.uio.no/jks/matpiv/html/node31.html but I'm not sure and I wanted the opinions of CFD, since in CFD softwares the vorticity is evaluated automatically.

Regards

Antonio

 Rami July 12, 2010 04:10

The vorticity definition (in tensor notation) is wik = (ui,k-uk,i)/2, while your expression is wx=ux,y-uz,z - which is wrong.

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