[Paraview] Calculation of Lambda2 using ParaView...
Stefan Melber
Stefan.Melber at DLR.de
Fri Jun 9 08:46:25 EDT 2017
Hi,
for vortex-detection i (tried) to calculate the lambda2-criterion (see
e.g. 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/.
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
_/_/_/_/_/_/_/_/_/_/ Institute of Aerodynamics
_/ _/ _ _ and Flow Technology
_/_/ | \ | |_| Transport Aircraft Branch
_/ |_/ |_ | \
Lilienthalplatz 7
Fields of activities: 38108 Braunschweig
Germany
o Numerical Windtunnel Simulation
o Aero-Acoustic Windtunnel Design Phone : +49 531/295-2836
o Numerical Optimization Fax. .: +49 531/295-2914
o Visualization Techniques
o High-Lift Aerodynamics Email : Stefan.Melber at DLR.de
o Glider-Aerodynamics Web ..: http://www.dlr.de/AS
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