Effect of Spike Truncation on the Acoustic Behavior of Annular Aerospike Nozzles

The work toward reusable single-stage-to-orbit launch-vehicle concepts has initiated several research activities\ud toward a suitable nozzle design, which (unlike bell nozzles) is expected to perform optimally over the entire flight regime. Of these concepts, the annular aerospike nozzle and its variants, linear and truncated, are among the most promising. Given the concern over the intensity of acoustic loading during takeoff, it is vital to carry out a detailed aeroacoustic characterization of aerospike nozzles with special attention to overexpanded conditions, which are\ud generally encountered during liftoff. In this work, an experimental investigation into aeroacoustics of an annular\ud aerospike nozzle of design Mach number (Md) of 2.0 has been carried out, and the results are presented. The effect of\ud truncation of the aerospike to 40 and 60% of the spike length on the acoustic field is also studied and compared with the full-length aerospike. Results show that, in the overexpansion regime, truncated conical aerospike nozzles have reduced acoustic (∼4–5 dB) levels until wake closure compared to the full-length aerospike and conventional\ud convergent–divergent nozzle, all operating at identical conditions. This noise reduction is predominantly in the region upstream of the nozzle exit. At the peak radiation angle (∼150 deg from the jet upstream direction), the acoustic levels are almost same for all of the nozzles investigated in the present study