[Josh]

Good day!

I have been modelling 2D URANS flows over airfoils. In a recent report, I had several plots of vorticity magnitude. A reviewer complained that the vorticity magnitude was not sufficient for vorticity detection. The reviewer suggested we plot the Q-criterion (second invariant of the velocity tensor) or Okubo-Weiss criterion (Weiss, J., The Dynamics of Enstrophy Transfer in 2‐Dimensional Hydrodynamics, Physica D: Nonlinear Phenomena, 48, pp. 273–294 (1991)) for better visualization.

After talking to people within my department, I think the reviewer's suggestion may be incorrect. I've never seen anybody use the Q-criterion in 2D and/or URANS flows. I argue that the Q-criterion (and Okubo-Weiss criterion) has no significance for 2D flows, which are what I'm studying. However, I can't describe why.

Am I right in my assumption? If so, why? Can you direct me to an example that has used either criterion in 2D and/or URANS flows?

Thanks for all your help.