Investigation Into the Operating Cycle of a Two-Dimensional Supersonic Wind Tunnel

Abstract

The operating cycle of an intermittent supersonic wind tunnel, while probably recognized, has never been denned rigorously, In this paper, the wind-tunnel operating cycle is divided into five distinct phases based on the character of the flow along the windtunnel axis. These phases are, in cyclic order, the nonstationary starting phase, the quasi-stationary starting phase, the stationary phase, the quasi-stationary closing phase, and the nonstationary closing phase. The first of the starting phases is treated both theoretically and experimentally for the case of the opening valve located downstream from the working section and experimentally for the case of the valve located upstream from the nozzle throat. These theoretical studies are based on an assumed wave pattern (subsequent to the breaking of the diaphragm) determined from results of shock-tube investigations and by application of an approximate theory for the solution of two-dimensional nonstationary flow problems due to Guderley. The quasi-stationary starting phase is studied theoretically by extending the stationary supersonic-subsonic jet theory in which the jet exit static pressure is less than the pressure in the region into which the jet is issuing. The theoretically postulated state of affairs during these phases is verified by obtaining experimentally a measured series of shadowgraphs and, thereby, determining the time history of the wind-tunnel starting process. The effect of condensation of water vapor on these phases is studied experimentally.