Call number: LD2668 .T4 1951 D6 / Master of Science

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.

In 1968, Finson and Probstein outlined a theory which could be used to analyse cometary dust tails. This theory is applied to a series of P/Halley images, obtained using the UK Schmidt Telescope. The theory is successful and shows that P/Halley underwent a series of major outbursts during early 1986. The duration of the outbursts is approximately 2 days. This value coincides with the 2.2day nuclear rotation period, estimated by other observers. The size of the dust grains varies from submicron to several hundred microns and their calculated orbital parameters indicate that a considerable fraction of the larger grains contibute to the Zodiacal Dust Cloud. A range of CCD and UK Schmidt images reveal dust features in the comae of comets P/Crommelin, P/Giacobini-Zinner and P/Halley. Intensity contours for many images exhibited a "swinging round" effect i.e. for each image there was a systematic change in the photometric axis from the central condensation outwards. This was attributed to radiation pressure effects. Astrometric images of P/Halley show sharp parabolic hoods. These hoods are discussed with reference to near-nuclear dust grain orbits. Preliminary results indicate that the rotation period of Hailey is at least a few days. Mie (1908), developed a method by which the general properties of scattering and emission by dust grains, can be used to model cometary thermal spectra. Such a method is applied to several P/Halley spectra, taken during April, 1986. The results indicate that the dust grains could be composed of both an absorbing (e.g. magnetite) and a dielectric (e.g. silicate) material. The interrelations between decaying comets and Earth-crossing asteroids are discussed. Optical and infrared observations indicate that comet P/Neujmin 1 may be a transitionary object. P/Arend-Rigaux however, is still very active, displaying a large dust coma, with anisotropic emission.

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