Investigation of Shrouded Nozzle Exit Pressure Changes.

Shrouded two- and three-dimensional, supersonic, cold flow nozzles were investigated. Altitudes up to 87,000 feet were simulated and nozzle inlet to ambient pressure ratios up to 400 were used. Pressure measurements were made along the nozzle exit plane and the shroud walls to determine the effect shrouding has on exit base pressure and the pressure distribution along the shroud walls. Comparisons were made in the blowdown wind tunnel using a variety of nozzle types, nozzle area ratios, and shroud lengths. Study results reveal that the pressure fields in the base region of the nozzle and along the shroud walls are dependent upon the geometry of configuration and operating altitude. Shroud wall pressures were found to act in the same manner as the base pressures by first maintaining a fairly constant pressure value until the chamber to ambient pressure ratio reached some critical value. When this condition occurred, the flow separated from the shroud with a resulting increase in the shroud wall pressures. Potential increases in nozzle assembly performance are possible from changing effective nozzle exit area and the resulting changes in the flow gas dynamics.