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> wrote: > 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 > <(531)%20295-2836> > o Numerical Optimization Fax. .: +49 531/295-2914 > <(531)%20295-2914> > o Visualization Techniques > o High-Lift Aerodynamics Email : stefan.mel...@dlr.de > o Glider-Aerodynamics Web ..: http://www.dlr.de/AS > > > ================================================================ > > > _______________________________________________ > Powered by www.kitware.com > > Visit other Kitware open-source projects at http://www.kitware.com/ > opensource/opensource.html > > Please keep messages on-topic and check the ParaView Wiki at: > http://paraview.org/Wiki/ParaView > > Search the list archives at: http://markmail.org/search/?q=ParaView > > Follow this link to subscribe/unsubscribe: > http://public.kitware.com/mailman/listinfo/paraview > >
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