Geometric Analysis of the Linear Expansion-Deflection Nozzle at Highly Overexpanded Flow Conditions

The effect of nozzle geometry on the thrust efficiency of the linear expansion-deflection (ED) nozzle concept has been investigated at highly overexpanded flow conditions. A new design method for generation of the ED nozzle contour is introduced and a factorial-based approach used to determine the effect of nozzle geometry on thrust coefficient. An area ratio of 17.6 was selected to represent a core stage nozzle and eight geometric parameters compared across sixteen separate configurations. Thrust coefficient was determined numerically from a time-dependent model using dry air as the working fluid. The numerical model was verified with respect to viscous effects and dimensional grid parameters, and then validated against experimental results to quantify sources of numerical error. Results were obtained for pressure ratios ranging from 5-50 to replicate highly overexpanded conditions where flow separation would occur in an equivalent conventional nozzle. Thrust coefficient in all ED nozzle configurations relative to the conventional nozzle ranged between 105-190% at low pressures and 90-120% at high pressures. The conclusions from the factorial analysis of ED nozzle contour geometry suggested that low curve radii and high inflection angles would further improve thrust coefficient for the flow conditions tested. The results show that an improvement in thrust relative to a conventional design can be expected at highly overexpanded flow conditions through the use of an ED nozzle configuration.