Experimental investigation of unsteady nature of shock waves induced by various ramps

The ramp induced shock wave boundary layer interaction (RI-SWBLI) has been investigated experimentally at different ramp angles in a Ma = 3 flow. The shock unsteady nature has been examined in detail by using a semi-quantitative processing of Schlieren images. The shock-wave locations are extracted to allow spectral analysis of the shock-wave oscillations. Results show that the shock motion is associated with the state of separation, which has been categorized into three classifications based on semi-quantitative Schlieren measurements, namely, unseparated, initially separated, and fully separated. The statistical analysis of the shock oscillation illustrates that the probability distribution function and power spectral density (PSD) along two locations of a certain height follow almost the same principles in the time–frequency domain. The PSD results show that significant variations of shock motion of lower location occur at 30° ramp interaction flow according to the PSD, which is characterized by a lower energy, wide range, and uniformly distributed motion. The probability of the reattachment shock events first rises at 24° ramp interaction flow. With increase in ramp angle, the axial position at the peak of the probability of shock events slowly transfers to upstream positions. Moreover, a conceptual model of the shock motion is proposed to preliminarily reveal the unsteady nature of shock induced by a RI-SWBLI, including three scenarios: In nonseparating interaction flows, the shock motion is mainly affected by the upstream turbulent boundary layer and the shear layer on the ramp. During the initial separation process, the shock wave motion is mainly affected by the pulsations of separation bubble. With full separation, impact movement is primarily controlled by newly designed aerodynamic ramp.