Dear Sir,

Other than Q- or lambda_2 criteria, Finite time Lyapunov exponent (FTLE) contours has been used quite popularly in recent days to detect the vortex boundaries from the purview of manifold theory in various flow dynamics problems. Apart from that, very recently, the concept of an eigenvector based `Rortex' or vortex vector has been introduced which can be efficiently used detect coherent structures.

"Rortex—A new vortex vector definition and vorticity tensor and vector decompositions" - Chaoqun Liu, Yisheng Gao, Shuling Tian, and Xiangrui Dong, Physics of Fluids, 30, 035103 (2018).

Best regards,

Chandan

Dear Sir,

Other than Q- or lambda_2 criteria, Finite time Lyapunov exponent (FTLE) contours has been used quite popularly in recent days to detect the vortex boundaries from the purview of manifold theory in various flow dynamics problems. Apart from that, very recently, the concept of an eigenvector based `Rortex' or vortex vector has been introduced which can be efficiently used detect coherent structures.

"Rortex—A new vortex vector definition and vorticity tensor and vector decompositions" - Chaoqun Liu, Yisheng Gao, Shuling Tian, and Xiangrui Dong, Physics of Fluids, 30, 035103 (2018).

Best regards,

Chandan

Interested

Thanks Chandan! Very helpful.

Dear Sir,

I look forward to reading about your new technique for vortex detection.

Best regards,

Chandan

Chandan: Have you used any of these tools? What is your personal experience? I think that our approach is somewhat straightforward based directly on Navier-Stokes equation. At this stage, it is valid for incompressible flows only. We are planning to write it up, for some specific example cases. We will provide comparison among various possibilities. At this point in time, we are not looking at FTLE. We will post all developments in RG.

Dear Sir,

I have used FTLE for understanding chaotic behaviour of the wake of a flapping wing in terms of fundamental vortex interactions. You may have a look at our recent publications as mentioned below:

1) Chandan Bose, Sunetra Sarkar (2018) : Investigating chaotic wake dynamics past a flapping airfoil and the role of vortex interactions behind the chaotic transition, Physics of Fluids, Volume 30, Issue 4, 047101. DOI: 10.1063/1.5019442.

2) Sandeep Badrinath, Chandan Bose, Sunetra Sarkar (2017) : Identifying the route to chaos in the flow past a flapping airfoil, European Journal of Mechanics/ B-Fluids, Volume 66, Pages 38-59, DOI: 10.1016/j.euromechflu.2017.05.012.

We are still investigating different interesting mechanisms from the saddle point approach in the Lagrangian framework.

However, the concept of Rortex is comparatively new as an Eulerian technique. We have not used it yet. I had the opportunity to review a couple of paper on this technique.

I would like to try implementing your technique in my problem once it is ready. I will follow your update.

Thank you,

Chandan

Dear Sir,

You can also take a look at Prof. Haller's criterion for identifying Lagrangian coherent structures, if you have not already:

https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/an-objective-definition-of-a-vortex/3CD781A3AEC4BA16571CBC2D9B4E973F

Thanks Mohd. Furquan! Yes, we are aware of this paper and its predecessor ones. We are also looking at RORTEX, as suggested by Chandan. Most of these coherent structure eduction techniques fall flat if you have vorticity and no vortex. Generically, turbulence is never always associated with vortex, as it is defined in terms of 3D vorticity field. We have already defined a better criterion for tracking disturbance field, without being bothered whether this is due to presence of additional vorticity or vortex, in:

Vortex - induced instability of an incompressible wall - bounded shear layer - Sengupta T.K., De, S., and Sarkar, S.; J. Fluid Mech. vol. 493, pp 277-286 (2003)

It is a shame that people have not paid attention in the contents of this paper. We are in the process of synthesizing all such techniques under one framework. It only works for incompressible flows, as governed by Navier-Stokes equation.

We are proposing disturbance mechanical energy and disturbance enstrophy transport equations as the physically relevant tools to not only identify vortices, but also for tracking any disturbance evolution. However, these are valid for incompressible flows. Both the methods are exact and derived from Navier-Stokes equation without any assumptions or simplifications.

Dear Sir Tapan K. Sengupta

This recent paper by the same group of authors might be of interest to you.

A selected review of vortex identification methods with applications

http://link-springer-com-443.webvpn.jxutcm.edu.cn/article/10.1007%2Fs42241-018-0112-8

Best regards,

Chandan

Thank you Chandan! Hopefully, we will also contribute to the field shortly!

Tapan Sengupta

I would be eager to read that.

Chandan