Buoyancy-Induced Columnar Vortices

Large-scale inherent instability of a thermally stratified air layer is exploited for deliberate formation of intense vertical column vortices. In hot-climate regions, buoyancy-driven vortices (``dust devils'') occur spontaneously, with core diameters of 1-50 m at the surface, heights up to one kilometer, with induced air flow of considerable angular and linear momentum. Meter-scale laboratory experiments have demonstrated the nucleation and sustainment of strong buoyancy-driven vortices over a plane heated surface driven by a controllable power source. Optical diagnostics includes high-speed video imaging and particle image velocimetry. It is shown that vortices having a nominal 10 cm diameter core with nearly-uniform vorticity distribution can be triggered by and ``anchored'' to small ground protrusions, and their circulation and angular momentum can be controlled by geometrical modifications of these surface protrusion and by simple flow vanes.