Flow Interaction Dynamics of Stagnation Point Injection in Mach 6 Quiet Flow

Stagnation-point injection experiments were performed using a [Formula: see text] half-angle cone with a 19-mm-radius spherical nose and a single, 1.93-mm-radius sonic jet in the center of the model directed into a Mach 6 quiet and a Mach 5.8 noisy freestream. The primary data consist of high-speed schlieren imaging at 76 kHz. Spectral analyses of the schlieren data were performed resulting in the observation of three key modes fundamental to the motions of the flow structures: 1) the vortex-coupled mode, 2) vortex-shedding mode, and 3) the longitudinal mode. The proper orthogonal decomposition was used to track the mode energy fractions as a function of thrust coefficient, while the dynamic mode decomposition was used to gain insight into the nature of the motions present in each mode. The spectral proper orthogonal decomposition is used to probe specific frequencies present in the jet reservoir spectra. As the thrust coefficient increases, the dominant mode changes from the vortex-coupled mode ([Formula: see text]) to the longitudinal mode ([Formula: see text]). The vortex-shedding mode is shown to be strongly correlated at [Formula: see text], but similar, weaker modes exist between 15 and 20 kHz.