FLASH LIGHTING INSTRUMENTATION FOR COLOR SCHLIEREN SHOCK-WAVE PHOTOGRAPHY

Single-shot color schlieren photography of supersonic flow phenomena r equires a technically complex flash light source. In particular, it sh ould be of ultrashort duration to minimize motion blur, of high intens ity to expose regular color film with only one flash, and should emit an almost ''white'' spectrum to provide the full scale of possible hue s. Furthermore, matching Settles' (1970) direction indicating color di ssection 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-filled linear flash lamps and a module of eight clos ely stacked U-shaped loops of micro gliding sparks. The spark module c onsists of a total of 280 individual micro gliding discharges which ar e all arranged uniformly within an area of 40 x 40 mm. 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 ab out 15% of volume at a total pressure of 1.5 bar. The emitted flash ha s 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 provid ing dear and sharp schlieren photos of shock waves which, for example, are purged from preceding ''phantom shock fronts''.