Integrated experimental and numerical study on shock wave evolution in underwater launch

• Development of a bidirectionally coupled Classic Interior Ballistics-Computational Fluid Dynamics (CIB-CFD) framework, integrating multiphase flow models (VOF, Schnerr-Sauer cavitation, SST k–ω turbulence), validated with high-precision experimental data (peak chamber pressure: 350 MPa; muzzle velocity error: 2.8%). • Comprehensive analysis of shock wave evolution mechanisms, revealing axial/radial wave propagation, bubble pulsation dynamics, and gas-water interaction effects, with modified empirical formulas predicting bubble parameters (pulsation period: 22 ms; maximum radius: 0.15 m) within 8% deviation. • Derivation of an underwater free-recoil formula incorporating water column momentum and propellant gas effects, providing accurate dynamic characterization for structural optimization of underwater launch systems. Understanding the evolution of shock waves during underwater launches is crucial for marine safety structures and personnel. Current studies lack a unified framework linking interior and intermediate ballistics in a bidirectional manner and have inadequate experimental validation regarding chamber pressure, projectile velocity, and flow field visualization. There is a need for quantitative analysis of the dynamics of bubble after-effects and their impact on shock wave evolution. To address these gaps, this study develops a bidirectionally coupled Classic Interior Ballistics–Computational Fluid Dynamics (CIB–CFD) framework that integrates Reynolds-Averaged Navier–Stokes equations with the Volume of Fluid multiphase model, the Schnerr–Sauer cavitation model, and the Shear Stress Transport (SST) k– ω turbulence model. Submerged firing experiments using a 7.62 mm automatic rifle in a glass enclosure provide data on chamber pressure, muzzle velocity, and flow field visualization for model validation. Simulations show a peak chamber pressure of 350 MPa at 0.3 ms and a muzzle velocity deviation of 2.8% from experimental values. Flow field analysis reveals that interactions between propellant gases and initial cavitation bubbles create distinct axial and radial shock waves along with bubble pulsations and vortex structures. The predicted bubble pulsation period of 22 ms and maximum radius of 0.15 m align closely with both simulations and measurements. Furthermore, an underwater free recoil formula based on momentum conservation principles is derived. The validated framework accurately predicts ballistic parameters, facilitating a comprehensive understanding of underwater shock wave evolution and aiding in the structural design of underwater weapon systems.