Thesis (Ph.D.)--Texas A & M University, 2004. / Title from caption (viewed on Feb. 8, 2008). Title from document title page. Includes bibliographical references. Available in PDF format via the World Wide Web.

Thesis (PhD) - Swinburne University of Technology, Centre for Molecular Simulation - 2007. / Dissertation submitted in fulfilment of requirements for the degree Doctor of Philosophy, Centre for Molecular Simulation, Faculty of Information and Communication Technologies, Swinburne University of Technology, 2007. Typescript. Includes bibliographical references (p. 151-161).

Thesis (MSc)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Thesis (M.App.Sc.) - Carleton University, 2007. / Includes bibliographical references (p. 102-106). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [143]-147).

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2006. / Includes bibliographical references (p. 73-76).

The concept of moving surface boundary-layer control, as applied to the Joukowsky and NACA airfoils, is investigated through a planned experimental program complemented by theoretical and flow visualization studies. The moving surface was provided by one or two rotating cylinders located at the leading edge, the trailing edge, or the top surface of the airfoil. Three carefully designed two-dimensional models, which provided a wide range of single and twin cylinder configurations, were tested at a subcritical Reynolds number (Re = 4.62 x 10⁴ or Re — 2.31 x 10⁵) in a laminar-flow tunnel over a range of angles of attack and cylinder rotational speeds. The test results suggest that the concept is indeed quite promising and can provide a substantial increase in lift and a delay in stall. The leading-edge rotating cylinder effectively extends the lift curve without substantially affecting its slope. When used in conjunction with a second cylinder on the upper surface, further improvements in the maximum lift and stall angle are possible. The maximum coefficient of lift realized was around 2.22, approximately 2.6 times that of the base airfoil. The maximum delay in stall was to around 45°. In general, the performance improves with an increase in the ratio of cylinder surface speed (Uc) to the free stream speed (U). However, the additional benefit derived progressively diminishes with an increase in Uc/U and becomes virtually negligible for Uc/U > 5. There appears to be an optimum location for the leading-edge-cylinder. Tests with the cylinder at the upper side of the leading edge gave quite promising results. Although the CLmax obtained was a little lower than the two-cylinder configuration (1.95 against 2.22), it offers a major advantage in terms of mechanical simplicity. Performance of the leading-edge-cylinder also depends on its geometry. A scooped configuration appears to improve performance at lower values of Uc/U (Uc/U ≤ 1). However, at higher rates of rotation the free stream is insensitive to the cylinder geometry and there is no particular advantage in using the scooped geometry. A rotating trailing-edge-cylinder affects the airfoil characteristics in a fundamentally different manner. In contrast to the leading-edge-cylinder, it acts as a flap by shifting the CL vs. α plots to the left thus increasing the lift coefficient at smaller angles of attack before stall. For example, at α = 4°, it changed the lift coefficient from 0.35 to 1.5, an increase of 330%. Thus in conjunction with the leading-edge- cylinder, it can provide significant improvements in lift over the entire range of small to moderately high angles of incidence (α ≤ 18°). On the theoretical side, to start with, the simple conformal transformation approach is used to obtain a closed form potential-flow solution for the leading-edge-cylinder configuration. Though highly approximate, the solution does predict correct trends and can be used at a relatively small angle of attack. This is followed by an extensive numerical study of the problem using: • the surface singularity approach including wall confinement and separated flow effects; • a finite-difference boundary-layer scheme to account for viscous corrections; and • an iteration procedure to construct an equivalent airfoil, in accordance with the local displacement thickness of the boundary layer, and to arrive at an estimate for the pressure distribution. Effect of the cylinder is considered either through the concept of slip velocity or a pair of counter-rotating vortices located below the leading edge. This significantly improves the correlation. However, discrepancies between experimental and numerical results do remain. Although the numerical model generally predicts CLmax with a reasonable accuracy, the stall estimate is often off because of an error in the slope of the lift curve. This is partly attributed to the spanwise flow at the model during the wind tunnel tests due to gaps in the tunnel floor and ceiling required for the connections to the externally located model support and cylinder drive motor. However, the main reason is the complex character of the unsteady flow with separation and reattachment, resulting in a bubble, which the present numerical procedure does not model adequately. It is expected that better modelling of the cylinder rotation with the slip velocity depending on a dissipation function, rotation, and angle of attack should considerably improve the situation. Finally, a flow visualization study substantiates, rather spectacularly, effectiveness of the moving surface boundary-layer control and qualitatively confirms complex character of the flow as predicted by the experimental data. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

A moving contact line is the idealized line of intersection between two immiscible fluids as one displaces the other along a solid boundary. The displacement process has been the subject of a large amount of theoretical and experimental research; however, the fundamental processes that govern contact line motion are still unknown. The challenge from an experimental perspective is to make measurements with high enough resolution to validate competing theories. An experimental method has been developed to simultaneously measure interface motion, dynamic contact angles, and local fluid velocity fields using micron-resolution Particle Image Velocimetry (µPIV). Capillary numbers range from 1.7 x 10^(⁻⁴) to 6.2 x 10^(⁻⁴). Interface velocities were measured between 1.7 µm/s and 33 µm/s. Dynamic contact angles were manually measured between 1.1 µm and 120 µm from the contact line, and calculated from µPIV data to within several hundred nanometers from the contact line. Fluid velocities were measured over two orders of magnitude closer to the contact line than published values with an increase in resolution of over 3400%. The appearance of a recirculation zone similar to controversial prediction below previously published limits demonstrates the power and significance of the method.

The laminar flow over a prolate spheroid was investigated via flow visualization and Laser-Doppler Velocimetry. Experiments were conducted in a water tunnel and the flow was visualized with dyes. The measurement of three-dimensional boundary layers required a special design of the laser optics. Attention was focused in the neighborhood of three-dimensional separation. The Vortex-Lattice method was employed to calculate the inviscid flow and the development of separated vortex sheets over a prolate spheroid. An approximate-method based on the assumption of local similarity was used to solve the boundary layer equations and calculate the line of open separation. A condition of vortex shedding along separation is proposed. The two schemes, viscous and inviscid, interact through the line of separation which is allowed to displace as the wake grows. Results are compared with flow visualization data for laminar separation and pressure data for turbulent separation. / Ph. D.

Pulsed ultrasound Doppler velocimetry proved to be capable of measuring velocities accurately (relative error less than 0.5 percent). In this research, the limitations of the method are investigated when measuring: in channels with a small thickness compared to the transducer diameter, at low velocities and in the presence of a flow reversal area. A review of the fundamentals of pulsed ultrasound Doppler velocimetry reveals that the accuracy of the measured velocity field mainly depends on the shape of the acoustic beam through the flow field and the intensity of the echo from the incident particles where the velocity is being measured. The ultrasonic transducer turned out to be most critical component of the system. Fundamental limitations of the method are identified. With ultrasonic beam measurements, the beam shape and echo intensity is further investigated. In general, the shape of the ultrasonic beam varies depending on the frequency and diameter of the emitter as well as the characteristics of the acoustic interface that the beam encounters. Moreover, the most promising transducer to measure velocity profiles in small channels is identified. Since the application of pulsed ultrasound Doppler velocimetry often involves the propagation of the ultrasonic burst through Plexiglas, the effect of Plexiglas walls on the measured velocity profile is analyzed and quantified in detail. The transducers ringing effect and the saturation region caused by highly absorbing acoustic interfaces are identified as limitations of the method. By comparing measurement results in the small rectangular channel to numerically calculated results, further limitations of the method are identified. It was not possible to determine velocities correctly throughout the whole channel at low flow rates, in small geometries and in the flow separation region. A discrepancy between the maximum measured velocity, velocity profile perturbations and incorrect velocity determination at the far channel wall were main shortcomings. Measurement results are improved by changes in the Doppler angle, the flow rate and the particle concentration. Suggestions to enhance the measurement system, especially its spatial resolution, and to further investigate acoustic wave interactions are made.