Transition of Edney shock–shock interactions due to the whipping phenomenon of liquid jet in supersonic crossflow

Abstract

In this paper, we experimentally study the unsteady dynamics of shock–shock interaction between the bow shock generated by a liquid jet in supersonic crossflow (LJISC) and an oblique shock. Images of shock–shock interactions were captured using high-speed focusing schlieren. Due to the whipping nature of the liquid jet, a coupling happens between the instantaneous bow shock shape and violent oscillations of the liquid jet. Proper orthogonal decomposition reveals that the dominant coherent structures of LJISC are convective and flapping modes, and these modes are responsible for unsteady variation in the local bow shock angle. An oblique shock emanating from a wedge is made to interact with the oscillating bow shock of a liquid jet near the sonic line. At this shock interaction location and for a constant momentum flux ratio between liquid jet and crossflow, unsteady transitions between the types of Edney shock–shock interactions were observed. The types of Edney shock–shock interactions that can occur depend on the local average bow shock angle and the momentum flux ratio. Support vector machine (SVM) model was used to classify three types of Edney shock–shock interactions based on ten features related to the nearest knee point, shock interaction point, and maximum penetration height. Using the SVM model, three dominant features that affect the type of shock–shock interaction were identified. Experimental results, when compared with shock polar, reveal some short-duration abnormal presence of overall regular interaction instead of overall Mach interaction regime.