An Experimental Parametric Study of Geometric, Reynolds Number, and Ratio of Specific Heats Effects in Three-Dimensional Sidewall Compression Scramjet Inlets at Mach 6
Since mission profiles for airbreathing hypersonic vehicles such as the National Aero-Space Plane include single-stage-to-orbit requirements, real gas effects may become important with respect to engine performance. The effects of the decrease in the ratio of specific heats have been investigated in generic three-dimensional sidewall compression scramjet inlets with leading-edge sweep angles of 30 and 70 degrees. The effects of a decrease in ratio of specific heats were seen by comparing data from two facilities in two test gases: in the Langley Mach 6 CF4 Tunnel in tetrafluoromethane (where gamma=1.22) and in the Langley 15-Inch Mach 6 Air Tunnel in perfect gas air (where gamma=1.4). In addition to the simulated real gas effects, the parametric effects of cowl position, contraction ratio, leading-edge sweep, and Reynolds number were investigated in the 15-Inch Mach 6 Air Tunnel. The models were instrumented with a total of 45 static pressure orifices distributed on the sidewalls and baseplate. Surface streamline patterns were examined via oil flow, and schlieren videos were made of the external flow field. The results of these tests have significant implications to ground based testing of inlets in facilities which do not operate at flight enthalpies.
Characterization of high speed inlets using global measurement techniques
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.
Simulation study of high power microwave generation by virtual cathode oscillation in coaxial vircator
Summary form only given, as follows. We have numerically simulated the high power microwave generation by virtual cathode oscillation in a coaxial vircator with 3 dimensional PIC code Magic. It is noted that the coaxial vircator has the advantage of an enhancement of power efficiency and gaining of narrow bandwidth frequency. The study is focused on the design of a diode structure for a coaxial vircator suitable for Chundoong IREB pulser (Max. 600 kV, 85 kA, 60 ns). It consists of a center annular cathode, a cylindrical meshed-anode and a reflector. The simulation results showed that the coaxial vircator can indeed be operated at the selected frequency with the narrow bandwidth and the microwave output power strongly depends on the position and geometry of the reflector. From this simulation results we expect that the maximum microwave output power will be obtained by the reflector of 4 cm in width and also 4 cm in distance away from the IREB, where the resonant frequency of microwave from coaxial vircator is simulated to be 6.577 GHz.