Flash lighting instrumentation for color schlieren shock wave photography

Abstract

Abstract. Single-shot color schlieren photography of supersonic flow phenomena requires a technically complex flash light source. In particular, it should be of ultrashort duration to minimize motion blur, of high intensity to expose regular color film with only one flash, and should emit an almost "white" spectrum to provide the full scale of possible hues. Furthermore, matching Settles' (1970) direction indicating color dissection method the source should be of an areal geometry to uniformly illuminate a tricolor filter in the source plane. Two different types of light sources have been constructed and compared to each other: an array of five Xe-filted linear flash lamps and a module of eight closely stacked U-shaped loops of micro gliding sparks. The spark module consists of a total of 280 individual micro gliding discharges which are all arranged uniformly within an area of 40 x 40 ram. Connected in a series and pulsed by a modified eight-stage 15 kV Marx-surge generator they are operated in a nitrogen gas atmosphere doped with xenon by about 15% of volume at a total pressure of 1.5 bar. The emitted flash has a peak light intensity of 29 Mcd and a flash duration of 292 ns FWHM. Advantageously in comparison to flash lamps, the flash of a gliding spark module is shorter and free of oscillatory afterglow, thus providing clear and sharp schlieren photos of shock waves which, for example, are purged from preceding "phantom shock fronts".

A local space–time conservation scheme and its application in shock wave propagation

“…The reasons causing these differences are the experimental conditions in Ref. [29] are not illustrated clearly and the resolution of the film used in the experiment is limited. Moreover, the computation is based on Euler equations, so those phenomena induced by the viscous effect are not captured.…”