Experimental study of high-enthalpy shock- tunnel flow. I - Shock-tube flow and nozzle starting time.

Abstract

The results of an experimental study of shock-tube and nozzle (reflected-shock-tunnel) flows for incident-shock Mach numbers ranging from 8.5 to 16.5 are reported. The test gas used in these experiments was either air or nitrogen and the driver gas was either hydrogen or helium. Incident-shock test times were measured using several diagnostic techniques for laminar boundary layers and for conditions at which boundary-layer transition occurred within the test-gas slug. The laminar boundary-layer data were found to be in excellent agreement with the theory. The data obtained for the transitional boundary-layer case are compared with the theory for fully turbulent boundary-layer flow because of the absence of an appropriate theory. The reflected-shock pressure dip frequently observed to follow the pressure plateau that occurs immediately after shock reflection was also studied. The results suggest that the dip is caused by an expansion wave generated upon initial interaction of the reflected shock with the driver-driven gas interface. The pressure dip was present to some degree for all combinations of driver and test gases studied. However, the dip was most pronounced for the case of hydrogen driving air possibly due to interface combustion. The starting time was studied in a 13° half-angle conical nozzle for two shock-tube Mach numbers, 16.5 and 11.5, using air as the test gas and hydrogen as the driver gas. Several diagnostic methods were used in the nozzle including microwave interferometers, photomultipiier tubes, and piezoelectric pressure transducers. The starting-time measurements made with these various techniques are shown to be generally in agreement. A result of these studies is that the measured time after shock reflection required to establish uniform flow at a given axial location in the nozzle can be reasonably predicted by integration of the quantity dx/(u — a).