Bow-Shock Instability and its Control in front of Hemispherical Concave Shell at Hypersonic Mach Number 7

Abstract

In this study, effectiveness of vortex manipulation by using passive control methods at hypersonic flows have been studied to control the bow-shock instabilities in front of negative curvature (concave) hemispherical shell. The force measurement and unsteady center pressure measurements were performed for hemispherical shell with no control and with three kind of passive controls such as spike at the center of cavity, breathing holes at the curved surface and crosswire along the diameter of hemisphere. The flow visualization for shock instability in front of all four geometries were performed using twin mirror Schlieren system and high-speed camera with 10,000 fps, which were synchronized with pressure measurements. The fluctuations in bow-shock were computed in time resolved manner by image processing methods and compared with pressure data. It is found that drag coefficient does not change significantly by using the different control methods, which were studied. The time resolved Schlieren image processing method is reliable in providing the information of shock fluctuations and the crosswire control method is most effective in subsiding the large shock deformation in the current study.

Mach 10 Bow-Shock Unsteadiness Modeled by Linear Combination of Two Mechanisms

“…For this flowfield, it is assumed that Δz is small when compared to the abscissa range of this tanh function. For a blunt-body model with a convex surface at Mach 7, Vashishtha et al [14] observed Δz to be typically small; large Δz were observed in ~1% of the data. Large Δz were correlated with and attributed to particle strikes.…”

“…There is a small but growing number of experimental studies of hypersonic bow-shock oscillations induced by freestream disturbances [10,11,14,15]. There have been several mathematical analysis and computational studies on freestream-unsteadiness-induced bowshock oscillations [16][17][18][19][20][21][22].…”

Mach Number Dependence of Flow Instability around a Spiked Body

“…A hemispherical cavity in front of hypersonic flow is also considered an effective flow control to increase aerodynamic drag and reduce heating at hypersonic flows, but it is also subjected to very highly unsteady flow-field, resulting in uncontrolled lift and side forces [5,6]. Few passive control methods have been suggested for frontal cavity and found effective in controlling the unsteadiness [7]. In active flow control methods, the counter-jet flow [1] has also been found effective method, creating flow spike to push the shock wave away from the blunt nose, but require additional system to inject high-pressure gas into the stagnation zone.…”