Buoyancy-induced, columnar vortices with application to power generation
Simpson, Mark William
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Buoyancy-induced, columnar vortices (dust devils) that are driven by thermal instabilities of ground-heated, stratified air in areas with sufficient insolation convert the potential energy of low-grade heat in the near-surface air layers into a vortex flow with significant kinetic energy. A variant of the naturally-occurring vortex is deliberately triggered and anchored within an azimuthal array of vertical, stator-like flow vanes that form an open-top enclosure and impart tangential momentum to the radially entrained air. The induced flow within the enclosure may be ultimately exploited for power generation by coupling the vortex to a vertical-axis turbine. The fundamental mechanisms associated with the formation, evolution, and dynamics of an anchored, buoyancy-driven columnar vortex that is formed within such an enclosure over a heated ground plane are investigated in laboratory experiments. Specific emphasis is placed on the dependence of the vortex cellular structure and vorticity production and sustainment mechanisms on the thermal resources and the magnitude and direction of the entrained flow that is regulated by the flow vanes. Manipulation of vorticity concentrations and advection are exploited in order to modify and optimize the available mechanical energy within the induced flow field and, therefore, the extractable power. Finally, anchored vortices are formed in the natural environment within a scaled field prototype of the flow enclosure using only insolation as the source of buoyancy. These field tests demonstrated formation and sustainment of energetic columnar vortices that enable potential thermomechanical link for tapping the gravitational potential energy of the unstable air layers for power generation.