Hi Andy,
i think i found the reason: i need the computation of (unsymmetrical)
eigenvalues for lambda2 - however it seems that the function
"eingenvalue" calculates only symmetric ones (see
https://www.paraview.org/ParaView/Doc/Nightly/www/py-doc/paraview.vtk.numpy_interface.algorithms.html).
How can i calculate the unsymmetric ones with ParaView?
Best regards,
Stefan
Hi,
Maybe compute each portion manually and check that against the correct
values. Also, verifying the gradient calculation is correct is another
thing to look at. If the grid isn't specified properly then the
gradient operation will likely be wrong.
On Fri, Jun 9, 2017 at 8:46 AM, Stefan Melber <stefan.mel...@dlr.de
<mailto:stefan.mel...@dlr.de>> wrote:
Hi,
for vortex-detection i (tried) to calculate the lambda2-criterion
(see e.g. https://en.wikipedia.org/wiki/Lambda2_method
<https://en.wikipedia.org/wiki/Lambda2_method>) with ParaView. The
way of calculation is based on this link
http://www.iesensor.com/blog/2016/01/24/using-paraview-to-visualise-vorticity-lambda2-vorticity-q-criterion/
<http://www.iesensor.com/blog/2016/01/24/using-paraview-to-visualise-vorticity-lambda2-vorticity-q-criterion/>.
However - the results are a kind of "wrong" - see attached
pictures: l2_solver.png shows what the flow solver writes out for
lambda2, l2_paraview.png shows what calculated with the algorithm
below.
Calculation of lambda2:
D = Gradients = [d_ij]
S = strain(Vel)
S = (D + D^T)/2
Omega = (D - D^T)/2
lambda = EigenValue_of(S^2 + Omega^2)
= EigenValue_of(S^2 + (D - S)^2)
= EigenValue_of(S^2 + (Gradients - strain(vel))^2)
lambda2 = lambda_Y
and in ParaView this mean
o Vector of velocity with "Calculator".................: Vel =
iHat*x_velocity+jHat*y_velocity+kHat*z_velocity
o Gradients of Vel with "GradientOfUnstructuredDataSet": switch on
"compute gradient" and name it "Gradients"
o Calculate lambda with "PythonCalculator".............: lambda =
eigenvalue(strain(Vel)**2+(Gradients - strain(Vel))**2)
o Caluclate lambda2 with Calculator....................: lambda2 =
lambda_Y
Does anyone see the error why the calculation of lambda2 with
ParaView does not work?
Remark: i contacted the author of the blog above already - seems
he never tested his calculation and has no idea what is "wrong".
Stefan
================================================================
_/ *Dr. Stefan Melber-Wilkending*
_/_/
_/ _/ Deutsches Zentrum für Luft-
_/_/_/_/_/_/_/_/_/_/ und Raumfahrt e.V. (DLR)
_/ _/ _/ _/
_/ _/ _/ _/ German Aerospace Center
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o High-Lift Aerodynamics Email : stefan.mel...@dlr.de
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