I want to visualize the vortex structures in the flow through a pipe junction having square cross-section.
If I select negative value of Lambda-2 criterion in paraview, I find structures near the walls. For positive values of Lambda2, the structures are away from the walls.
Also, I am getting same pattern of vortex structures with positive values of Lambda2 which I do get with positive value of Q criterion.
So,
1) should I select positive values of Lambda2 or negative values?
2)Do Q- and Lambda2- criteria give similar structures?
It is my experience that for confined flows the picture of vortex detected by the lambda2=0 criterion is not very useful and a negative value produce somehow better results.
Considering the original paper, I think you can find the answer 2) in Table 1
https://www.researchgate.net/profile/Fazle_Hussain/publication/231865270_Hussain_F_On_the_identification_of_a_vortex_JFM_285_69-94/links/54d236ab0cf28e069723aaf2/Hussain-F-On-the-identification-of-a-vortex-JFM-285-69-94.pdf
Article Hussain, F.: On the identification of a vortex. JFM 285, 69-94
Thank you Filippo,
I have gone through the article.
I could understand few things, I am a beginner.
I am using openfoam and I used to visualize the vortex structures using contours of Lambda2 in paraview.
It is showing a range of values for Lambda2(negative to positive through zero). If I select negative values, my results are not matching with the vortex structures published in literature. Only when I select positive value of Lambda2, they are matching.
(One more thing I noticed in my simulation is that: negative value of Lambda2 is showing vortex structures near the wall while positive value shows in the main stream direction.)
I request you to clarify this.
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