Unstart Modes of a Streamtraced Busemann Inlet in Mach 6 Quiet Flow

A shape-transitioning Busemann intake, called the Indiana Inlet, was studied in the Purdue Mach 6 quiet tunnel under various levels of downstream flow blockage from high pressure air injection. The back pressurization of the scramjet isolator led to various system behaviors, including the identification of four distinct quasi-steady operating modes: scramjet mode, ramjet mode, soft unstart, and hard unstart. Hard and soft unstart modes resulted in the cowl shock becoming disgorged from the mixed contraction, causing massive flow spillage and loss of performance. An oscillatory 200 Hz flowfield phenomena, often called "big buzz," was identified from high speed schlieren images, pressure traces, and spectral analysis during soft unstart mode cases. Additionally, a precursor to big buzz, called little buzz, was identified from spectral methods during ramjet mode conditions which were close to soft unstart.