Experimental Effects of Nozzle Geometry on Flow Efficiency at Low Reynolds Numbers

摘要

This paper discusses the design and testing of 10 two-dimensional nozzles for studying supersonic flow at Reynolds numbers ranging from 150-2000. The 10 nozzles involve three classes: an ideal contour for two-dimensional expansion, a 15 deg cone, and the ideal contour widened for the displacement thickness, each cut to 25,50, and 100% axial lengths. The last nozzle is a 100% -axial-length ideal contour class; that is twice the thickness to see the effect of endwall boundary-layer growth. The nozzles are tested in a vacuum chamber at subatntospheric chamber pressures to achieve low pressure and Reynolds numbers. The nozzle's coefficient of thrust efficiency is approximately 80% for Reynolds numbers greater than 1500, and the data suggest the efficiency drops below 60 % at 400. The error becomes significant at a low Reynolds number due to pressure measurement error, which reduces the quality of the results. No significant improvements are observed between the nozzle contours or with lower expansion ratios. Significant improvements are observed with the 2x thick nozzle, which suggest endwall boundary layers are important