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CHARACTERIZATION OF HIGH SPEED INLETS USING GLOBAL MEASUREMENT TECHNIQUES

Che Idris, Azam

[Thesis]. Manchester, UK: The University of Manchester; 2014.

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Abstract

After the end of the NASA space shuttle programme, there has been resurgence of interestin developing a single stage-to-orbit spacecraft. The key technology to realize this dream isthe airbreathing scramjet engine. The scramjet concept has been around for decades, butmuch work is still needed in order to eliminate the remaining obstacles to develop apractical working prototype of the engine. Many such obstacles are related to the inletwhich functions as the main compression unit for the engine.Typically, a high speed inlet is designed to function properly in a single flight condition. Suchan inlet would experience adverse flow conditions related to various shock-shockinteractions, viscous effects, shock-boundary layer interactions, and many other flowphenomena at off-design conditions. The traditional mechanism to mitigate the adverse flowconditions is by varying the inlet geometry at off-design conditions. There are still gaps inunderstanding the behaviour of inlets at off-design conditions and the effectiveness ofvariable geometry as inlet flow control. This is partly due to complex flow diagnostics setup,which limits the type, quantity and quality of information that can be extracted from theinlet flow.The first objective of this thesis was to develop a global inlet measurement system that canprovide an abundance of information on inlet flow. The pressure sensitive paint method wasemployed together with other methods to provide comprehensive understanding on inletflow characteristics. Calculation of Mach number at the isolator exit using the isolatorsidewall pressure map was successfully demonstrated. The measurement of Mach numberat the isolator exit has allowed for performance of the inlet to be calculated without theneed for intrusive flow diagnostics tools used by previous researchers.The global measurement system was then employed to investigate the characteristics of thescramjet inlet operating at various off-design conditions. Complex shock structures wereobserved at the inlet cowl entrance as the angle-of-attack was increased. The relationship offlow quality and inlet performance was examined and discussed. General improvements onthe inlet performance were obtained if the size of separation on the compression ramp wasreduced. The inlet was also observed to perform poorly when compression shocks impingedon the inner cowl surface.Cowl deflections were demonstrated to be effective in controlling the internal flow of theinlet and improving its performance. An exploratory study on the role of micro-vortexgenerators to control boundary layer separation on scramjet inlets has been included aswell. Strategies for optimizing an inlet at off-design conditions were analysed, and it wasfound that any variable geometry combination must maintain high throat-to-freestreamMach number ratio in order to preserve high inlet performance.