Self-Synchronizing Stroboscopic Schlieren System for the Study of Unsteady Air Flows.

摘要

A self-synchronizing stroboscopic schlieren system developed for the visualization of unsteady air flows about aerodynamic bodies in wind tunnels is described. This instrument consists essentially of a conventional stroboscopic schlieren system mollified by the addition of electronic and optical elements to permit the detailed examination of phenomena of cyclic nature, but of fluctuating frequency. An additional feature of the device makes possible the simulation of continuous slow motion, at arbitrarily chosen rates, of particular flow features. Physically, the instrument is a schlieren system having two light paths with displaced light sources and focal points but using common primary reflectors. One of these light paths, utilizing a steady light source, is intercepted by a phototube, which receives signals in the form of changes of light intensity corresponding to fluctuations of the air stream density. The output of this phototube in turn triggers a stroboscopic light source, thereby producing a stationary image of an oscillating disturbance in the other light path. Simulated slow motion is obtained electronically by causing the flash of the stroboscopic light to lag the synchronizing signal from the phototube by a constantly increasing increment of time. Circuit descriptions and an itemized list of the components used are presented.