Suppression of Jet Noise by Staged Water Injection during Launch Vehicle Lift-Off

Abstract

Jet noise during the lift-off of a launch vehicle is complicated by the simultaneous flow of multiple jets, and their deflection by jet deflectors. Further, the presence of the launch pedestal, the service structure, and the moving vehicle itself, act as reflecting surfaces, which contribute to the noise environment. The present work involves the suppression of noise as measured at different parts of the launch vehicle in a small-scale replica of a full launch pad, for different locations of the vehicle along its vertical lift-off trajectory. The primary source of noise is the two jets emerging from the base of the launch vehicle at a Mach number of 3.38. Noise is suppressed by water injection at different locations in the launch pad such as the upstream and downstream edges of the jet deflector cover-plate, bottom and top of the launch pedestal, and at two different locations on the service structure. The effect of staged injection of water, i.e., without and with injection at different heights relative to the position of the jets, as the vehicle is at different locations in its trajectory, is examined. It is found that sustained suppression of noise is obtained only with injection of water in successive stages closer to the nozzle exit, as the jet position is moved up. The effect of angle of injection of water is investigated to verify previously reported results that an injection angle of 60°, i.e., along the flow, is superior to injection at 90°to the jet. The effect of injection pressure shows an optimum that supports the effective atomization of the injected water jets into droplets due to shear by the gas jet flow. Investigation with hot jets shows increased noise levels by at least ~2 dB relative to cold jets of nearly the same nozzle-exit Mach number. However, an increased reduction of noise by water injection is apparent with hot jets. The reduction is nearly independent of the jet temperature in the 600-900 K range. The present results collectively confirm the qualitative applicability of different previous studies on single free jets to the complicated launch vehicle noise scenario.

Numerical simulation of particle jet formation induced by shock wave acceleration in a Hele-Shaw cell

“…Other technological applications include thrust-vectoring of high-speed vehicles (Perurena et al, 2009), solid-fuel rocket motors (Cai et al, 2003;Shimada et al, 2006), noise reduction in jet engines and rocket launch pads (Krothapalli et al, 2003;Ignatius et al, 2008;, operation of turbomachinery in particle-laden flows (Hamed et al, 2006), spray deposition (Dolatabadi et al, 2004;Samareh and Dolatabadi, 2008), mining safety (Ugarte et al, 2017), heterogeneous explosives , and drug-delivery systems using micro shock-tubes (Truong et al, 2006). Dense high-speed particle-laden flows also occur in nature.…”

“…Gas-turbines operating in regions with suspensions of sand particles in the air are subject to substantial degradation due to particle deposition on turbine blades ( Hamed et al, 2006 ). Water injection systems have been used to reduce sound intensity at rocket launch pads ( Ignatius et al, 2008 ), and it might be possible to utilize similar systems to reduce jet noise ( Krothapalli et al, 2003 ), which is especially important around air-crafts during takeoff. Shock wave interaction with particle clouds has been extensively studied over the last fifty years.…”

Suppression of High Mach Number Rocket Jet Noise by Water Injection

“…3 that the reduction in the noise level due to water injection is less sensitive to X=D e in the downstream region than in the upstream. It is known that the major noise source near the tip of the potential core is significantly affected by injection within the core [35]. Because the present range of X=D e is well within the potential core length, the reduction in the mixing noise is nearly insensitive to the injection location, as observed in the downstream direction.…”

“…The two attenuation mechanisms observed were decrease of jet velocity by momentum transfer between liquid and gas phase and reduction of jet temperature due to partial vaporization of the injected water. The need to have sustained water injection near the rocket nozzle exit during the liftoff phase was recently reported by Ignatius et al [35]. In fact, multistage water injection was found to be very effective in the launch scenario.…”

Simulations of rocket launch noise suppression with water injection from impingement pad

“…Alternatively, for rocket launch or aircraft carriers, it is more practical to inject water from the impingement pad (launch pad or deflector). Ignatius et al 6,7 and Ragaller et al 8 have considered supersonic jets impinging on a perpendicular plate and have shown, experimentally, that injecting water from microjets through the impingement plate can reduce noise. They conjectured that water injection from the ground plane reduces the sources of sounds due to impingement.…”