Experimental Investigation of Noise Suppression in Liquid Rocket Engine via Water Injection

The development of effective water-injection systems is essential for mitigating acoustic loading from high-thrust rocket engines during launch. To address this challenge, Beihang University established the Liquid Propellant Engine Acoustic Rig (LPEAR), an experimental facility capable of generating supersonic jet flows up to Mach 3 and stagnation temperatures of 3300 K—closely approximating the exhaust conditions of main-stage rocket engines. Using this platform, an experimental water-injection system was developed to investigate the acoustic suppression mechanisms of high-temperature supersonic plumes. The study focuses on the payload-bay acoustic environment, where upward-propagating jet noise imposes significant structural loading during liftoff. Controlled experiments systematically examined the influence of both injection velocity and water-to-plume mass-flow-rate ratio (MFRR) on jet noise, with MFRR ranging from 0 to 12 and injection velocity from 8.2 to 33.1 m/s. Results reveal two key behaviors not previously reported in the literature: 1) at low MFRR, water injection can slightly increase highfrequency noise due to enhanced fine-scale turbulence generated by plume–water interaction; 2) at higher MFRR, the maximum achievable noise reduction is governed by injection velocity, as higher velocities improve water– plume coupling, promote faster vaporization, and form denser mist regions. The resulting water mist further suppresses high-frequency noise through viscous and relaxation absorption, although the detailed quantitative behavior requires further investigation. These findings provide experimental insight and scaling references for optimizing water-injection parameters to improve acoustic suppression efficiency and reduce payload-bay acoustic loading in high-temperature rocket exhaust environments.