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<font size="-1">Hi,<br>
<br>
<br>
for vortex-detection i (tried) to calculate the lambda2-criterion
(see e.g. <a class="moz-txt-link-freetext"
href="https://en.wikipedia.org/wiki/Lambda2_method">https://en.wikipedia.org/wiki/Lambda2_method</a>)
with ParaView. The way of calculation is based on this link
<a class="moz-txt-link-freetext"
href="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/</a>.<br>
<br>
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.<br>
<br>
Calculation of lambda2:<br>
<br>
</font><font size="-1"><tt>D = Gradients = [d_ij]</tt><tt><br>
</tt><tt>S = strain(Vel)</tt><tt><br>
</tt><tt><br>
</tt><tt>S = (D + D^T)/2</tt><tt><br>
</tt><tt>Omega = (D - D^T)/2</tt><tt><br>
</tt><tt><br>
</tt><tt>lambda = EigenValue_of(S^2 + Omega^2) </tt><tt><br>
</tt><tt> = EigenValue_of(S^2 + (D - S)^2) </tt><tt><br>
</tt><tt> = EigenValue_of(S^2 + (Gradients - strain(vel))^2)
</tt><tt><br>
</tt><tt> </tt><tt><br>
</tt><tt>lambda2 = lambda_Y</tt><tt><br>
</tt></font><font size="-1"><br>
and in ParaView this mean<br>
<br>
</font><font size="-1"><tt>o Vector of velocity with
"Calculator".................: Vel =
iHat*x_velocity+jHat*y_velocity+kHat*z_velocity</tt><tt><br>
</tt><tt>o Gradients of Vel with "GradientOfUnstructuredDataSet":
switch on "compute gradient" and name it "Gradients"</tt><tt><br>
</tt><tt>o Calculate lambda with "PythonCalculator".............:
lambda = eigenvalue(strain(Vel)**2+(Gradients - strain(Vel))**2)</tt><tt><br>
</tt><tt>o Caluclate lambda2 with Calculator....................:
lambda2 = lambda_Y</tt><tt><br>
</tt></font><font size="-1"><br>
<br>
<br>
Does anyone see the error why the calculation of lambda2 with
ParaView does not work?<br>
<br>
Remark: i contacted the author of the blog above already - seems
he never tested his calculation and has no idea what is "wrong".<br>
<br>
Stefan<br>
<br>
</font> <br>
<br>
<tt>================================================================</tt><tt><br>
</tt><tt>
</tt><tt><br>
</tt><tt> _/ <b>Dr. Stefan
Melber-Wilkending</b></tt><tt><br>
</tt><tt> _/_/
</tt><tt><br>
</tt><tt> _/ _/ Deutsches Zentrum für
Luft- </tt><tt><br>
</tt><tt> _/_/_/_/_/_/_/_/_/_/ und Raumfahrt e.V.
(DLR) </tt><tt><br>
</tt><tt> _/ _/ _/ _/
</tt><tt><br>
</tt><tt> _/ _/ _/ _/ German Aerospace
Center </tt><tt><br>
</tt><tt> _/_/_/_/_/_/_/_/_/_/ Institute of
Aerodynamics </tt><tt><br>
</tt><tt> _/ _/ _ _ and Flow
Technology </tt><tt><br>
</tt><tt> _/_/ | \ | |_| Transport Aircraft
Branch </tt><tt><br>
</tt><tt> _/ |_/ |_ |
\ </tt><tt><br>
</tt><tt> Lilienthalplatz
7 </tt><tt><br>
</tt><tt> Fields of activities: 38108 Braunschweig</tt><tt>
<br>
</tt><tt> Germany</tt><tt>
<br>
</tt><tt> o Numerical Windtunnel Simulation
</tt><tt><br>
</tt><tt> o Aero-Acoustic Windtunnel Design Phone : +49
531/295-2836 </tt><tt><br>
</tt><tt> o Numerical Optimization Fax. .: +49
531/295-2914 </tt><tt><br>
</tt><tt> o Visualization
Techniques </tt><tt><br>
</tt><tt> o High-Lift Aerodynamics Email : <a
class="moz-txt-link-abbreviated"
href="mailto:Stefan.Melber@DLR.de">Stefan.Melber@DLR.de</a></tt><tt><br>
</tt><tt> o Glider-Aerodynamics Web ..: <a
class="moz-txt-link-freetext" href="http://www.dlr.de/AS">http://www.dlr.de/AS</a></tt><tt><br>
</tt>
<br>
<tt>================================================================</tt><tt><br>
</tt><br>
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