Pressure Oscillations from Cavities with Ramp

Study on supersonic flow over wall-mounted cavities with different ramp angles is carried out experimentally. Experiments include instantaneous shadowgraph visualization and unsteady pressure measurements. In the case of cavities with ramp angles of 90, 75, and 60 degrees, four different types of waves were observed in the supersonic flow above the cavity. The shear layer appeared predominantly wavy in nature. The wave system observed in the case of cavities of 90, 75 and 60 degrees is distinctly different from that in cavities of 45, 30, and 15 degrees. In the case of cavities with higher ramp angles, high-amplitude tones were observed and the presence of an upstream-traveling acoustic wave could be confirmed. A cavity with a ramp angle of 45 degrees was found to reduce the amplitude of oscillations. An increase in amplitude of oscillations at various locations inside the cavity has been observed for cavities with ramp angles of 30 and 15 degrees. This is in contrast to the cavity with a ramp angle of 45 degrees. The reasons for this ambiguous behavior could not be ascertained. The presence of a forward-moving acoustic wave could not be identified in the cavities with ramp angles of 45,30, and 15 degrees. Temporal mode switching occurring in cavities with higher ramp angles was confirmed by spectrogram studies.