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When a thin delta wing with high leading-edge sweep is placed at incidence in a stream, the fluid separates from the surface at the leading edges and coils up to form a pair of symmetrically placed vortices above the upper surface of the wing. This flow pattern is stable up to high incidence, but at extreme high incidence, the stable vortex core appears to burst or rapidly diffuse. The present research was done as part of a general program to study the vortex bursting phenomenon about sharp-edged delta wings. The aim was to determine the bursting position at different angles of attack and the effect on the wing performance. It was found that the bursting occurs first downstream of the trailing edge and then moves rapidly upstream with increasing incidence. The wing stalls when the bursting point occurs at a position upstream of the wing's trailing edge. The pressure distributions on a sharp-edged rectangular wing were also measured in the present research and the overall normal force coefficient was obtained by the graphical integration of surface pressures. It was found from the pressure distributions that the flow pattern changes from one type to another in the range from ∝= 10° to ∝= 15°. The overall normal force coefficient reaches its first maximum value at 17° incidence. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The aerodynamics of a set of two-dimensional, stationary elliptic cylinders with eccentricity of 0.44, 0.92 and 0.98 is studied experimentally during the organised wake condition (R=2x10⁴-10⁵). The results indicate the effect of eccentricity and angle of attack on mean and unsteady pressure coefficients, Strouhal number and wake geometry, the three important parameters in the aeroelastic instability study. In conjunction with the available literature, the information presented here attempts at providing better understanding of the bluff body aerodynamics in the region between the two extreme cases of circular cylinder (e=0) and flat plate (e=∞) . The cylinder eccentricity and attitude has considerable effect on vortex shedding frequency, with variation of the Strouhal number in the range 0.037-0.274. Although basing Strouhal number on projected dimension or wake width reduces its dependence on angle of attack, the use of transverse distance between the separation points provides, in addition, a smoother transition even at higher eccentricities and smaller angles of attack. The measurement of fluctuating pressure in the narrow band around the Strouhal frequency showed substantial dependence on the Reynolds number at zero angle of attack, particularly for the ellipses of high eccentricity Considerable phase difference may exist between the pressure signals, however, it has negligible effect on the unsteady lift. The thesis also presents analytical results on the location of shear layer separation as obtained using Görtler's series in conjunction with mean pressure profile. The analytical data compared favourably with the results of flow visualisation through Schlieren technique. The high speed movie of the near wake region gave preliminary information about the location of the first vortex and the oscillations of the separating shear layers. The rise and decay of the unsteady pressure in the vortex formation region appeared to substantiate the visual observations. In general, the wake geometry ratio varied around the Kármán stability value of 0.281. The correlation of spanwise results clearly emphasized the three dimensional character of the unsteady aerodynamics. In general, the spanwise variation of fluctuating pressure is enhanced with increase in angle of attack. The phase data suggest inclination of the vortex line at the model to be ≲11°. Increase in angle of attack results in improved alignment of the vortex line with the cylinder axis. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

This thesis presents an experimental investigation of the fluctuating lift (or side force) coefficient on fixed two dimensional rectangular cylinders for various free stream turbulence intensities and scales. The measurements are made using turbulence producing devices such as grids and circular rods placed upstream of the stagnation line of the model. Measurements are reported for three fixed rectangular prisms with B/H of .5, .67 and 1 where H is the frontal dimension and B is the streamwise width of the body. The method of measurement made it possible to vary the body span so that the correlation of the fluctuating side force over the body span could be investigated. It was shown that for low turbulence intensity, the spanwise correlation of the fluctuating side force over the square cylinders decreases by a large amount with increasing span. For higher turbulence intensity this decrease was reduced, and for U'/U≃10% there was essentially no decrease of fluctuating lift coefficient with increase of span. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Good combustion is required to maximize steam generation and avoid emissions in the wood waste fired boilers found frequently in the pulp and paper industry. The combustion process is assisted if velocities above the grate are minimized, if gases in the combustion zone are mixed intimately, and if gaseous combustion is concentrated above the grate. A 1/15 scale replica of a power boiler was constructed for isothermal flow modelling of the flow field above the grate, the overfire air jets and the furnace up to the generating banks. The flow was made visible with smoke, and velocities were measured with a pulsed wire anemometer. It was found that a very non uniform velocity profile occurred above the fuel grate because the under grate plenum did not adequately diffuse the under grate air flow. Also, non perforated areas of the fuel grate near the furnace walls caused recirculation zones to occur above the grate near the front wall. The recirculation zones of the overfire air jets caused high velocities to occur above the grate as well. A large space between the front wall and the front overfire air nozzles on the side walls, caused vertical stratification of the flow, in which gases rising from the grate, near the front wall did not mix with the overfire air. At part load, reduced velocity in the overfire air jets caused vertical stratification of the flow as well, in which mixture of gases rising from the grate and overfire air occurred well above the fuel grate. At high nozzle velocities, gases were well mixed, throughout the cross section, large recirculations occurred and mixing was concentrated near the fuel grate. Established models for jets for free turbulent jets do not accurately represent opposing banks of jets. Centerline velocity is overpredicted by a factor of two or more, and deflection of the jet are greatly underpredicted by the models. Throw and penetration, calculated with the models do not give reasonable predictions, indicating the need for more sophisticated models. At high overfire air flow rates, oscillation of the overfire air jets was observed, with a period in the order of one second. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate