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Benefiting from the development of increasingly advanced high speed cameras,flow visualization and analysis nowadays yield detailed data of the flow fieldin many applications. Notwithstanding this progress, for high speed andsupersonic flows it is still not trivial to capture high quality images. Inthis study we present a Schlieren setup that uses pulsed LEDs with highcurrents (up to 18 Ampere) to increase the optical output to sufficient levels.The bright and short pulses, down to 130 nanoseconds, allow detailed and sharpimaging of the flow with a high spatial resolution adequate for supersonicflow. The pulse circuit and pulse width determination are explained in detail.As a test case we studied the near field of a 2 mm diameter sonic jet injectedtransversely into a supersonic cross flow. This is a model flow for fuelinjection in scramjet engines, which is not yet fully understood. Owing to thehigh resolution and accuracy of the images produced by the newly developedsystem we prove the existence of a large (density) gradient wave traveling inthe windward subsonic region between the Mach barrel and the bowshock, whichhitherto was observed only in some numerical studies but not yet shown inexperiments. Furthermore, we demonstrate with this Schlieren setup thattime-correlated images can be obtained, with an interframe time of 2microseconds, so that also flow unsteadiness can be studied such as themovement of shock waves and trajectories of vortices. The obtained results ofthe jet penetration height are presented as a power law correlation. Theresults of this study show that the designed setup using a low-cost LED andlow-cost control system is a high potential option for application invisualization studies of high speed flows.

Schlieren study of a sonic jet injected into a supersonic cross flow using high-current pulsed LEDs