Constant chamber pressure throttling of an expansion-deflection nozzle

Abstract

Thrust throttling at constant chamber pressure is desirable for certain advanced engine applications. An expansion-deflection (E-D) nozzle is by its very nature altitude-compensating and throttleable. Additionally, the chamber pressure, Pc, can be maintained constant with pintle axial displacement. A study was conducted to examine the effect of throttling an E-D nozzle on nozzle performance. The analysis used the two-dimensional axisymmetric method of characteristics to calculate nozzle wall static pressure and nozzle thrust. The experimental program consisted of cold flow testing and engine testing. Using the cold-flow data (measured net thrust and chamber pressure), nozzle thrust coefficients were calculated. The effect of throttling on throat discharge coefficient and the effect of open and closed wakes on plug base pressure were studied. Test variables included throat area, nozzle pressure ratios, and throat flow angle. Analytical and experimental agreement was good. Calculated static pressure variations along the nozzle contour were in good agreement with those experimentally measured.