Cranz-Schardin visualisation of a hypersonic cone with gas injection

Abstract

We have developed a five-picture Cranz-Schardin system for Schlieren flow visualization on a gun tunnel facility at the University of Southern Queensland to aid the study of unsteady shock systems in nominally steady hypersonic flows. The system produces useful images at framing rates up to about 1 MHz even though the system development was constrained by a very modest budget. The system uses multiple LED light sources driven by an in-house designed device that delivers a high current pulse to each LED with a programmable time delay between each pulse. The images are captured using four separate, black and white video devices and one digital still camera. The utility of the system is demonstrated by imaging gas injection from an annulus on a 10 degree half angle cone positioned at the exit of the contoured Mach 7 nozzle. Visualisation of the cone without gas injection demonstrates that the half angle of the conical shock is approximately 13.9 degrees (the Taylor-Maccoll conical shock angle at Mach 7 for an inviscid cone half angle of 10 degrees is 12.9 degrees). The gas injection condition used in these experiments disturbed the flow field upstream of the injection point to such an extent that the thickness of the shocked flow at the point of injection was larger than the no-injection case by a factor of approximately two. The conical shock angle in the case of injection increased to approximately 19 degrees, and a variation in this shock angle of approximately 1 degree was observed during the nominally steady, facility run time.