Fluid and Combustion Dynamics in Axisymmetric and Perisymmetric Supersonic Combustion Flowpaths

An experimental comparison of the fluid and combustion dynamics between axisymmetric and perisymmetric ethylene-fueled supersonic flowpaths was made in a Mach 4.5 high-enthalpy flow. The perisymmetric shape can be characterized as roughly elliptical, with sharp corners at its major axis vertices. High-speed imaging of the flow luminescence and wall pressure measurements were performed simultaneously. Four different combustion modes (scram mode, scram-ram transition, ram mode, and unstart) were observed by altering the global equivalence ratio. Time-resolved measurements revealed that the mode transitions for the perisymmetric model occurred earlier than the axisymmetric model. The instantaneous data showed transient phenomena such as upstream flame propagation in the combustor, reverse flame propagation into the isolators, and the propagation of the pseudo-shock. In addition, an inlet buzz was observed for the perisymmetric model. The time-resolved high-speed images and the pressure data revealed that inlet unstart and restart repeatedly occurred during the inlet buzz. The results of a Fourier transform analysis indicated that acoustic resonance within the flowpath was the primary mechanism for the inlet buzz of the perisymmetric model.