[Paraview] Vorticity calc algorithm?

[Moreland, Kenneth]

The implementation of the compute derivatives filter has been around a while so the author probably hasn't seen your email. I'm not super familiar with the code, but I believe the vorticity is computed from the first order derivative of the vector field.

It is not actually using a central difference scheme to compute the gradients. Instead, it is treating the field as a piecewise linear field (or piecewise quadratic or piecewise cubic depending on the cell type) based on the volumes of the cells. The derivatives are then computed in the middle of the piecewise C1 continuous parts of the cells from the known function.

You can take a look at the source for the algorithm here:

http://vtk.org/gitweb?p=VTK.git;a=blob;f=Filters/General/vtkCellDerivatives.cxx;h=4debdf45eeb7a11e98062ab2d9efa65e938433b6;hb=ab4dc579c340167b6b3ae6cd82b3fd645642796a

Vorticity is computed between lines 169 and 216.

-Ken

From: Jean Hertzberg <Hertzberg at Colorado.EDU<mailto:Hertzberg at Colorado.EDU>>
Date: Wednesday, February 11, 2015 at 12:01 PM
To: "paraview at paraview.org<mailto:paraview at paraview.org>" <paraview at paraview.org<mailto:paraview at paraview.org>>
Subject: [EXTERNAL] [Paraview] Vorticity calc algorithm?

Hi
I asked this last week, but got zero response. Please help me, or point me towards the right documentation:
Exactly what algorithm is used to calculate vorticity in the Compute Derivatives filter? Is it a first or a second order central difference scheme for gradients, or does it use the circulation method?

Thanks

Jean Hertzberg

Dept. Mechanical Engineering
University of Colorado, Boulder

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