An experiment on aerodynamic nozzles at M = 2

Abstract

In an aerodynamic nozzle a convergent primary nozzle is housed within an afterbody which is surrounded by a shroud. Part of the external flow is captured thereby and compressed by the under-expanded primary jet. At the design point this system is not as efficient as a convergent-divergent nozzle but its off-design performance should be better. In the experiment axi-symmetric models were used. The shrouds were cylindrical externally and either cylindrical or convergent-divergent internally. With each model the thrust and afterbody pressure distributions were measured at jet pressure ratios up to 20 with a free-stream Mach number of 2.0. Component drags were estimated indirectly from these measurements. For comparison, the thrust of unshrouded convergent and convergent-divergent nozzles was measured under the same conditions. With the cylindrical shrouds the effects of shroud length, shroud diameter and boundary-layer thickness were investigated. The greatest thrust developed by these models was about 5% less than that of the equivalent convergent-divergent nozzle. With the convergent-divergent shrouds the main variable studied was the ratio shroud throat area/shroud exit area. The thrust of the best model was some 9% less than that of the convergent-divergent reference nozzle. In the case of one cylindrical shroud the internal flow was studied in detail by surface pressure measurements and radial traverses.