Suppression of High Mach Number Rocket Jet Noise by Water Injection

Abstract

The present work experimentally investigates suppression of the sound level from an underexpanded jet of Mach number 2.8 by water injection. The jet is produced by a solid rocket motor being static test fired. Water is injected from a radial distance of 5.2 jet diameters, at different axial locations from the exit of the nozzle, at two different angles of injection relative to the downstream jet axis. The ratio of mass flow rates of water to the nozzle exhaust gas (referred to as the mass flow rate ratio) and the injection pressure are varied independently. Acoustic measurements are performed at a radius of 30 jet diameters, over angles in the range of 30-130 deg, relative to the downstream jet axis. Sound levels continuously decrease by 10 dB with the increase in the angle of observation. With water injection, higher levels of reduction in sound are observed in the upstream quadrant. Injection closer to the nozzle exit leads to better reduction, mainly due to suppression in the high-frequency range when observed from downstream, but it is almost in the entire frequency range as observed at the upstream locations. At intermediate mass flow rate ratios, an optimum injection pressure exists for maximum noise suppression, due to the penetration of water to the potential core and its evaporation there at high injection pressures. The results affirm that the validity of many past studies obtained on water injection to suppress noise levels on simulated jets can be extended to an actual rocket situation.

Transient influence of water injection on the flow field of a hot launch in a W-shaped silo

“…And the mass flow rate ratio between the liquid water and missile exhaust is 2.86, which is in the range of 2–5, as used in Sankaran et al. 34 Since the missile is climbing during launch, the dynamic layering method 5 of the dynamic mesh tool is adopted to simulate the movement. Two stationary boundaries are set for the missile’s movement: one for the compressed mesh and the other for the expanding mesh.…”

“…And the mass flow rate ratio between the liquid water and missile exhaust is 2.86, which is in the range of 2–5, as used in Sankaran et al. 34…”

Microphone Phased Array to Identify Liftoff Noise Sources in Model-Scale Tests

“…There are indications of similar tests for the Japan Aerospace Exploration Agency M-V vehicle [9,10]. Sankaran et al [11] provide a summary of various launch acoustic efforts.…”

Flow Field and Acoustic Investigations of the Launch Vehicle Environment during Lift-off

“…Several research studies utilize sub-scale models of actual launch vehicle configuration [1][2][3][4][5][6][7][8], including water injection effects in some cases. Most of these studies used actual scaled down rocket motors to obtain exact launch vehicle exhaust conditions, as an attempt to perfectly simulate the launch vehicle scenario in a smaller scale.…”