Numerical investigation of water injection position effects on supersonic jet noise using an Eulerian–Lagrangian framework

As demands for noise reduction in aerospace grow, supersonic jet noise from rocket engines poses a significant concern during launches. A water-based acoustic suppression system is considered an effective method. However, the mechanisms and design factors remain poorly understood. To investigate the impact of water injection position on jet noise, this study employs an Eulerian–Lagrangian framework that incorporates droplet breakup, evaporation, and coupled heat and mass transfer in a supersonic jet. Far-field acoustics are predicted using the Ffowcs Williams–Hawkings (FW–H) analogy. The overall numerical framework, encompassing both flow and acoustic modeling, is validated against available experimental data with good agreement. Results show that water injection modifies the flow and acoustic characteristics of the supersonic jet. Across all injection positions, weak shock cells form near impact regions, compressing the jet core and altering shear-layer development. Near-nozzle injection induces strong disturbances, enhances mixing and evaporation, and forms continuous vapor bands, while downstream injection produces weaker localized effects. Far-field acoustic analysis reveals that noise suppression depends on water injection position, being most effective near the nozzle, decreasing with distance, and becoming negligible beyond five nozzle diameters. These findings highlight that injection position critically governs jet flow and acoustic radiation, and that early intervention in jet-core development is essential for effective far-field noise control.