Turbulence is all around us. It's in the swirl of coffee and milk in a latte, unfurling along the wings of airplanes and the sides of cars, churning the blood in your heart after the valve snaps closed. Yet we still don't fully grasp all of its rules.
I am not in academia any longer, so I don’t have access to the full paper, but I would be really curious about the boundary conditions they see. They claim to have a region of isolated turbulent mixing, however, this would mean that they no longer have a no-slip boundary layer, something that I find hard to believe in a fully fluid system like this. Instead, I imagine the best they could likely do is have a boundary region over which the Reynolds number decreases rapidly as you move from the turbulent region to the non-turbulent region.
As an aside, this reminds me of some really cool research that a friend of mine did back in grad school which is kind of like the inverse of this. They created an active system in which turbulent mixing was bound to the surface of a vesicle (video)
The full paper seems to be on the arxiv as well: https://arxiv.org/abs/2211.00771 . I find this extension very convenient for situations like this.
Thank you! If I am understanding right, I think my guess was pretty bang on. Fig. 3b shows the energy dissipation from the center of the vortex blob moving outward and shows a steep drop off past where they define their edge (brown line).
Also, thank you so much for the extension recommendation! I have journal access through work for journals I go to frequently, so I forget about arxiv sometimes.