# Is it possible to generate one half of a Karman Vortex Street?

The Karman Vortex Street is a type of phenomenon which is generally illustrated by examples in which a long, solid, smooth circular cylinder moves at constant velocity through a fluid. The long axis of the cylinder is perpendicular to the relative velocity vector. Eddies form on the downstream side of the cylinder and detach at a regular temporal rate. The eddies form alternately in two places either side of the "flow axis". The downstream wake behind the cylinder can be described as a series of alternating, counter-rotating vortices. Karman vortex streets can also be generated by cylinders with other cross-sections, even by flat plates.

My Question

Is it possible to generate a "vortex street" which consists of a single series of co-rotating vortices?

Example

Consider an infinitely wide river with a flat bottom and water flowing steadily from west to east and a solid, smooth cylinder with semi-circular x-section attached (curved surface upwards) to the riverbed with its long axis running north-south. Now is it possible, under certain combinations of fluid viscosity, fluid velocity and cylinder geometry, that, on the downstream side of the cylinder, tubular vortices parallel to the cylinder will periodically form, grow and detach and be carried downstream at regular time intervals?

• Don't airfoils do what you want? Or am I misunderstanding your goal? Jan 17, 2015 at 22:10
• @KyleKanos. No that is not what I am thinking of. I have revised my example to try and make it clearer what I seek. Jan 18, 2015 at 1:06
• This might be the case of breaking out your trustiest CFD program and looking at a few different Reynold's numbers. Jan 18, 2015 at 2:34
• @KyleKanos. Good suggestion, but getting into CFD would be a major project for me. Jan 18, 2015 at 12:42

## 1 Answer

Yes. These kind of corotating Karman Vortex Streets do exist.

I have made real video's about this, when I noticed it in nature. No CFD, but Real stuff.

https://www.youtube.com/watch?v=iXfkaFmpnL4&list=PLgUc9kJnDMMExJivT2dWh9dAjdYYUgOFE&index=8

I was studying Turbulence, and I am more interested in other aspects of this flow. (Optics)

But in the video you could see how this single vortexes or creating this "half street", they are same times divided to smaller ones and united to a single one. But anyhow, clearly only another half of the typical vortex street.

It should be noted that all Vortexes are "single vortexes". I actually have even better example of this kind of Vortex. You can actually found this patented dropstructure, which energy dissipation is based on such a one half vortex street.

So it's basically a open channel nozzle. At this case the one-sided rotation becomes very apparently, as there is a strong continuous counter-current at the riverbanks. You can see some of the benefits of the structure live here.

• Welcome to Physics! Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. Jun 19, 2015 at 15:35
• Yes thankyou. It appears to be what I was asking for - a single series of co-rotating vortices. Although I cannot be 100% sure from the video that all the vortices are rotating the same way (clockwise). Also there is a separate but perhaps complimentary series of vortices, less well-defined, flowing from the other side of the red-daubed rock (at top of the screen). Jun 20, 2015 at 21:17
• You can find more videos in my channel, and see even really clean one; <youtube.com/…> here every single big vortex rotates to same direction. It's not just so easy to see, cause there is no color, and the youtube video quality is so low. Jun 21, 2015 at 7:21
• @JokelaTurbine - Mainly for interest. I took 4th photo from top of page here in 2009 and it is now in dozens of places on the web (no credit, no \$ :-) ). THere seem to be vortex streets off a number of the islands and the rear ones appear closer to linear that double sided. Probably not the case but appearance is interesting. Jul 9, 2015 at 8:43
• @RussellMcMahon - I see trails of cumulus clouds (presumably) downwind of islands (above which I presume ascending thermal air pockets have produced the clouds). This is interesting (to me) in its own right but I don't see von Karman vortices :-). Jan 2, 2016 at 13:53