Study on Control of Unsteadiness and Flow Asymmetry in Linear Aerospike Nozzles

The unsteadiness in flow over a linear aerospike nozzle is analyzed by a two-dimensional numerical simulation. Variations in the separation locations on two sides of the full-length plug nozzle, with the increase in nozzle pressure ratios (NPRs), are compared to study the asymmetry. For the linear aerospike nozzle considered, the flow becomes unsteady after NPR=12. The amplitude of the pressure fluctuation over time is compared at different locations on the surface of the nozzle, starting from the separation point to a few locations downstream. The amplitude of the pressure fluctuation increases from the separation location, reaches a peak value, and then starts decreasing. Interaction between the trapped recirculation bubble and the overexpansion shock causes the asymmetry. An optimum truncation at x/L=0.50 is able to arrest the separation shock foot at the tip of the truncated base, thereby eliminating the pressure fluctuation over the plug surface. Interaction of the recirculation zones behind the truncated base causes a minor fluctuation from NPR=12 until NPR=17. Nevertheless, the fluctuations are negligible when compared to the fluctuation over the full-length plug surface. The fluctuations die out at NPR=17 when the truncated plug is nearing closed-wake operation.