MIXING ENHANCEMENT NEAR SCRAMJET FLAME HOLDERS

THE UNSTEADY FLOW PHENOMENA AROUND REALISTIC SCRAMJET FLAME HOLDERS WILL BE STUDIED USING AN EFFICIENT TIME-ACCURATE NUMERICAL SCHEME. NUMERICAL SIMULATION OF A SUBSONIC RAMJET HAS SHOWN AN INTERACTION BETWEEN THE LARGE-SCALE VORTICES AND ACOUSTIC WAVES AT A CHARACTERISTIC NONACOUSTIC EIGENFREQUENCY. IN SUPERSONIC RAMJETS, ACOUSTIC WAVES WILL PROPAGATE UPSTREAM ONLY THROUGH THE SUBSONIC RECIRCULATION ZONE AND MAY INTERACT WITH THE SEPARATED SHEAR LAYER, RESULTING IN SIMILAR OSCILLATIONS. THIS ASPECT OF FEEDBACK MECHANISMS WILL BE STUDIED IN DETAIL AS A FUNCTION OF MACH NUMBER IN THE PROPOSED STUDY. THE EXISTENCE OF THIS TYPE OF FEEDBACK HAS IMPORTANT IMPLICATIONS FOR ENHANCING MIXING AND HENCE INCREASING COMBUSTION EFFICIENCY. SPECTRAL ANALYSIS AND CROSS CORRELATION OF THE TIME VARIATION OF THE PRESSURE AND VORTICITY FLUCTUATIONS AT VARIOUS LOCATIONS WILL BE EMPLOYED TO IDENTIFY THE CHARACTERISTIC FREQUENCY OF OSCILLATION AND WAVE PROPAGATION. THE PROPOSED STUDY WILL DETERMINE WHETHER COUPLING BETWEEN ACOUSTICS AND VORTEX MOTION CAN BE SUSTAINED IN THE VICINITY OF A SCRAMJET FLAME HOLDER AND HOW IT IS AFFECTED BY THE MACH NUMBER OF THE FLOW.