Aerodynamic Characterization of Linear Aerospike Nozzles in Off-Design Flight Conditions

Abstract

Spike surface flowfields and base wake behaviors of clustered linear aerospike nozzles under the presence of external flow were characterized using surface pressure measurements, flow visualizations using the background-oriented schlieren method, and theoretical modeling. The test model consisted of three clustered cell nozzle modules or a nonclustered two-dimensional nozzle with an exit Mach number of 3.5, followed by a straight section and a contoured spike. The model was exposed to an external flow of Mach 2.0 to simulate off-design transonic flight conditions. The measured surface pressure distributions indicated that the entire flowfield on the spike surface became more two-dimensional under the presence of external flow. Periodic compressions and expansions of the cell nozzle jet were eliminated, but the pressure continued to increase downstream. The results of the flow visualizations found that this was mainly governed by the external flow that controls the jet expansion by forming a slip surface. This mechanism also made the spike base pressure higher than environmental pressure. The physics-based model predicted the measured surface pressure distribution well and explained the mechanism behind the influence of external flow. The effects of the external flow showed improvements in thrust performance in off-design flight conditions.