Experimental study of high-enthalpy shock- tunnel flow. II - Nozzle-flow characteristics.

The duration of uniform flow and wall boundary-layer growth have been measured in the conical nozzle of a reflected-shock tunnel operating at high-enthalpy conditions. Experiments were performed in air for shock-tube Mach numbers of 16.5 and 11.5, with corresponding initial driven-tube pressures of 0.5 and 10.0 torr, respectively. Several different diagnostic techniques were used to measure the uniform-flow period and the results are compared. Radiation-intensity and electron-density measurements were found to be the most sensitive flow indicators. The boundary-layer displacement-thickness growth on the nozzle wall was determined for both of the aforementioned experimental conditions using velocity and density profiles deduced from Pitot-pressure and stagnation-point heat-transfer measurements. Good agreement was found between experimental and theoretical Pi tot pressures at comparable inviscid area ratios. The measured boundary-layer and displacement thicknesses are compared with the results of two typical prediction techniques. ART I of this paper describes the studies of the shock-tube flow and nozzle starting time. The purpose of Part II is to describe the subsequent nozzle-flow experiments in which the test time and the boundary-layer growth were experimentally determined for high-enthalpy reflected-shock conditions. The results are presented here because boundary-layer measurements obtained for such flow conditions are relatively scarce in the literature. The nozzle boundary layer was investigated with the aid of radial surveys of Pitot pressure and stagnation-point heattransfer rate at several axial locations. These measurements were used to deduce the local velocity and density relative to the corresponding values on the nozzle centerline, and the experimentally determined profiles were used to calculate the appropriate boundary-layer displacement thickness. Many authors111 have proposed techniques that may be used to predict the boundary-layer growth on the wall of a conical nozzle, and the present results can be used to test these techniques. However, the major emphasis of Pt. II has been placed on the experimental measurements, with only a limited comparison with prediction. Two particular prediction techniques2-5 have been selected as typical and the experimentally determined boundary-layer and displacement thicknesses are compared with these. The experimental apparatus used in this work was described in detail in Pt. I. The first part of Sec. 2 of Pt. II presents the experimentally determined test time at different locations in the nozzle and compares the results of the various diagnostic techniques. Section 2 concludes with a discussion of the boundary-layer data obtained at each of the experimental conditions and compares the results with existing prediction techniques.