Thesis (Ph. D.)--Stanford University, 1978. / "Printed in 2003 by digital xerographic process on acid-free paper"--P. after T.p. Includes abstract (p. iv). eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (p. 213-217).

Aerodynamic flow control can improve aerofoil performance by influencing the natural growth of boundary layers, which develop on the surface of vehicles moving in viscous fluids. Many active and passive techniques have been developed to reduce drag and/or increase the lift of aerofoil sections. The work presented in this thesis is concerned with the active excitation of the boundary layer on the suction side of aerofoil sections through momentum transfer via a secondary flow. The secondary flow was achieved by air passing through an air breathing device (ABD) which was implemented in the aerofoil surface. This resulted in an almost tangential and uni-directional fluid interaction. Numerical and experimental work showed a beneficial influence of the secondary flow on the aerodynamic characteristics of the studied aerofoil sections. A Taguchi analysis was initially used to confirm findings from previous work on the use of an ABD on a NACA0012 aerofoil section. The resulting parameter ranking showed general agreement with previous data in that the most important parameters are the gap-size i.e. the length over which the two fluids are in contact and the velocity gradient between the two fluids. However, it also raised questions that required an additional in-depth analysis of the parameters governing the flow control process. Due to the greater importance to the modern aviation industry of the NACA65-415 aerofoil section this particular cambered aerofoil section was used for further investigations. This study highlighted the importance of the velocity gradient between the main and secondary flows as well as the location of interaction of the ABD. In addition the gap-size is also important. Consideration of the power requirements for the ABD indicated that this may limit exploitation of the device. An evolutionary search strategy based on genetic algorithms, was employed to optimize the air breathing geometry. This optimisation produced non-intuitive geometries which revealed the importance of promoting an inner fluid recirculation in the device. Finally experimental data in a closed loop wind-tunnel showed trends which were in general agreement with the numerical predictions. However, the measurements indicated significantly greater enhancements of lift forces than those predicted by thenumerical investigation.

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Complex policy problems in today’s world require sound evidence for good decisions. Yet what constitutes sound evidence can often itself become a matter of political contention. Using original qualitative interview, focus group and document analysis, this thesis finds both that many Canadian organizations with a mandate for communicating scientific information (knowledge transfer) are working to bring together researchers and end-users into various forms of direct contact (known as interaction practices) and that different social groups have concerns with these interactions. Through using interaction practices to improve communication efforts by establishing end-user/researcher relationships, the socially constructed boundaries that exist between science and politics become blurred. When the science communicated has controversial political implications, this blurring becomes problematic, “polluting” the wider credibility of the science communicated. This thesis uses “boundary theory” to argue that organizations engaging in knowledge transfer must be aware of these risks, and in controversial political topics, work to span rather than blur these boundaries, in order to protect scientific credibility necessary to successfully communicate scientific information in politically controversial situations.

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Receptivity refers to the generation of boundary layer instability waves by external disturbances. Recent work by M. E. Goldstein has set the general framework for the different types of boundary layer receptivity mechanisms. Therefore, it is now understood that receptivity occurs near the leading edge or at locations downstream where the boundary layer undergoes a rapid streamwise adjustment. The present work analyzes the receptivity due to a free-stream acoustic wave interacting with a suction surface--hard wall junction. In this case, receptivity occurs because of the rapid changes in wall suction distribution. Analytical expressions for the amplitude of the generated instability wave have been derived and numerical estimates provided for parameter values typical of hybrid laminar flow control applications. The importance of the junction receptivity as compared to other receptivity mechanisms has been assessed.