Leapfrogging of smoke rings

The following examples concern "leapfrogging of smoke rings", that means several vortex structures are blown - with a certain temporal lag - out of a small hole ("mouth") and chase one another.

Since this "game" cannot be simulated in an unbounded domain, some artificial boundaries have to be introduced. Thus, these examples demonstrate the quality of the "do nothing" boundary conditions. All flows are driven only by a given `pressure drop'; the corresponding numerical concepts can be found in http://www.featflow.de/paper/HRT.ps.gz, and in Stefan Turek's CFD-book, Springer

The original ideas for these simulations are taken from Van Dyke's "Album of Fluid Motion" and are experimentally verified by the smokers at our institute...

• Leapfrogging of 2 smoke rings (same speed) at low Reynolds number
• Leapfrogging of 2 smoke rings (different speed) at low Reynolds number
• Leapfrogging of 2 smoke rings (different speed) at medium Reynolds number
• Leapfrogging of several smoke rings (same speed) at medium Reynolds number