Numerical investigation on thrust characteristics of an annular expansion-deflection nozzle

The thrust characteristics of a large-expansion-ratio annular expansion-deflection (ED) nozzle are investigated based on detailed flow pattern simulations. The purpose is to build a bridge between the nozzle internal flow pattern and nozzle thrust performance. The present work traces flow parameters along typical streamlines to demonstrate the nozzle flow pattern, partitions the nozzle exit plane based on its flow features to evaluate thrust contributions of each thrust coefficient contributor in different sub-areas, and monitors flow parameter distributions in the nozzle exit plane at 22 nozzle pressure ratios to interpret the developing histories of nozzle thrust coefficients. The present simulations show that the shocks generated in open wake mode are both inevitable and indispensable, while the shocks generated in closed wake mode contribute negatively to thrust performance. Three basic requests for designing a high-performance ED nozzle are clarified, which are to ensure high-quality expansion at the nozzle throat, to smooth out the reflected shock in open wake mode, and to diminish the strong near-wall shock generated in closed wake mode. An interesting and counter-intuitive phenomenon, namely, the existence of the reflected shock in open wake mode not only consumes the ability of the exhaust flow to do work but also improves the overall nozzle thrust performance, is explained. This is because the reflected shock deflects lateral-going exhaust flow to the axial direction. When this reflected shock disappears, a sudden drop in the nozzle thrust coefficient history takes place.