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Thesis (Ph.D. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 250-259).

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xix, 172 p.; also includes graphics. Includes bibliographical references (p. 168-172).

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Studies on the effect of transport properties coupled with the interaction of fluid dynamics and combustion in acoustically forced laminar hydrogen jet diffusion flames have been performed using the planar laser-induced fluorescence (PLIF) technique. These unsteady diffusion flames are of particular interest because they are reproducible turbulent-like events that can be investigated to gain insight into turbulent combustion. Results reported herein add to the ongoing effort of understanding the complex transport processes taking place in the flames encountered in most modern heat-producing and power-producing devices. Fuel transport properties (i .e. fuel Lewis number, LeF) were varied by fuel dilution with various levels of helium (He) or argon (Ar). The fuel stream ofBurkeSchumann type hydrogen flames was acoustically excited by using a loudspeaker and the two-dimensional OH and temperature fields were measured. PLIF measurements were performed using an intricate two-laser, two-camera system; digital image analysis was implemented to reduce the large image data set obtained. The temperature of the unsteady flames departed significantly from the steadystate temperature as predicted by previous researchers. It was found that, regardless of LeF, unsteady He-diluted flames had maximum flame temperatures at some point during the speaker -oscillation that were always higher than the maximum temperatures of the H2-Ar flames. This was contrary to the trends seen in steady flames. An increased H2 mass flux to the flame zone in the unsteady H2-He flames was the reason for this observation since mass diffusion becomes important in the driven flames due to increased mass gradients and the difference in diffusivity of hydrogen in the diluents used. Low turbulence intensities (i.e.low frequency) allowed the flames to respond steadily to the changing flowfield. The structure of the reaction zone of unsteady flames at this low frequency was altered (i.e. stretched or compressed) slightly and, in general, these flames resembled the steady flames structurally. At high frequency, however, the flames responded to the imposed flow oscillation by considerable reaction zone stretch/compression. Results obtained from the present experiments suggest that, depending on the Lewis number, the flame temperature responds differently to the stretch imparted on the flame by the unsteady flowfield. These Lewis number effects were evidenced by both the low and high frequency flames, however, they were most obvious in the high frequency cases. The temperature of flames with LeF ~ l increased/decreased when the reaction zone thickened/thinned. On the other hand, flames with LeF < l increased/decreased in temperature when the reaction zone thinned/thickened. These trends competed with the thermal and mass transport processes present in the high-curvature regions of the flames.

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Experiment shows that the steady axisymmetric flow past a sphere becomes unstable in the range 120 < Re < 300. The resulting time-dependent nonaxisymmetric flow gives rise to nonaxisymmetric vortex shedding at higher Reynolds numbers. The present work reports a computational investigation of the linear stability of the axisymmetric base flow. When the sphere is towed, fixed, or otherwise constrained, stability is determined solely by the Reynolds number. On the other hand, when the sphere falls due to gravity, the present work shows that a additional parameter, the ratio of fluid density to sphere density (β = ρ(f)/ρ(s)) is involved. We use a spectral technique to compute the steady axisymmetric flow, which is in closer agreement with experiment than previous calculations. We then perform a linear stability analysis of the base flow with respect to axisymmetric and nonaxisymmetric disturbances. A spectral technique similar to that employed in the base flow calculation is used to solve the linear disturbance equations in streamfunction form for axisymmetric disturbances, and in a modified primitive variable form for nonaxisymmetric disturbances. For the density ratio β = 0, which corresponds to a fixed sphere, the analysis shows that the axisymmetric base flow undergoes a Hopf bifurcation at Re = 175.1, with the critical disturbance having azimuthal wavenumber m = 1. The results are favorably compared to previous experimental work.

In this work, a two-dimensional model representing the vortices that animals produce, when they are flying/swimming, was constructed. A D{shaped cylinder and an oscillating airfoil were used to mimic these body{shed and wing{generated vortices, respectively. The parameters chosen are based on the Reynolds numbers similar to that which is observed in nature (104). In order to imitate the motion of ying/swimming, the entire system was suspended into a water channel from frictionless air{bearings. The position of the apparatus in the channel was regulated with a linear, closed loop PI controller. Thrust/drag forces were measured with strain gauges and particle image velocimetry (PIV) was used to examine the wake structure that develops. The Strouhal number of the oscillating airfoil was compared to the values observed in nature as the system transitions between the accelerated and steady states... As suggested by previous work, this self-regulation is a result of a limit cycle process that stems from nonlinear periodic oscillations. The limit cycles were used to examine the synchronous conditions due to the coupling of the foil and wake vortices. Noise is a factor that can mask details of the synchronization. In order to control its effect, we study the locking conditions using an analytic technique that only considers the phases.. The results suggest that Strouhal number selection in steady forward natural swimming and flying is the result of a limit cycle process and not actively controlled by an organism. An implication of this is that only relatively simple sensory and control hardware may be necessary to control the steady forward motion of man-made biomimetically propelled vehicles. / by Cyndee L. Finkel. / Thesis (Ph.D.)--Florida Atlantic University, 2013. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

Thesis (Ph. D.)--Brigham Young University. Dept. of Mechanical Engineering, 2003. / Includes bibliographical references (p. 133-136).

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