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.

abstract: ABSTRACT The Spirit landing site in Gusev Crater has been imaged by the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) camera more than thirty times since 2006. The breadth of this image set allowed a study of changes to surface features, covering four Mars years. Small fields of bedforms comprised of dark material, and dark dust devil tracks are among the features revealed in the images. The bedforms are constrained within craters on the plains, and unconstrained in depressions less than 200m wide within the topography of the Columbia Hills, a ~120m-high structure in center of Gusev. Dust devil tracks appear in many images of the bedforms. Within the Columbia Hills, three bedform fields approximately 180m2 and composed of fine dark basaltic sand were studied, using five HiRISE images taken from 2006 to 2014. Both bedform crests and the dust devil tracks superimposed on them were evaluated for change to azimuth and length, and for correlation between the features. The linear to slightly sinuous transverse crests ranging from less than 1m to 113m in length and two to three meters in wavelength, are primary bedforms. During the study they shifted as much as 33 degrees in azimuth, and individual crests moved on the surface as much as 0.75m. The greatest changes corresponded to a global dust storm in 2007. Average crest movement was documented at the rate of 0.25m per year. Rather than moving progressively, the crests eventually returned to near their original orientation after the storm. The dust devil tracks, reflecting a more complex wind regime, including vortex development during diurnal heating, maintained predominantly NW-SE orientations but also reflected the effects of the storm. The observed modifications were neither progressive, nor strictly seasonal. The apparent stability of the bedform geometry over four seasons supports the predictions of the Mars Regional Atmospheric Modeling System (MRAMS): low speed (1-7.5 ms-1), daily alternating winds of relatively equal force. Crest profiles were found to be nearly symmetrical, without slipfaces to indicate a preferential wind direction; this finding also is supported by the MRAMS model. / Dissertation/Thesis / Masters Thesis Geological Sciences 2016