Vertical water entry of projectiles with surface seal

Abstract

The water entry of a three-dimensional slender projectile with a constant vertical velocity is investigated numerically, and experiments are done to validate numerical results. We limit the scope of this work to the cavity forming stage at which surface seals. Typical experiments are carried out in a launching system. A pressure-based compressible multiphase solver combined with the Kunz cavitation model is developed within the OpenFOAM® platform. The numerical and experiment results show a good agreement. The time-dependent change regularity of the drag coefficient, pressure distribution, air-entrained cavity evolution, and flow characteristics inside the cavity are elaborated. Their relationships with the key parameter Froude number are also discussed. Results indicate that the drag coefficient after the impact phase is approximately equal to that in supercavitation case, and it is generally of the Froude number. Cavity shapes are generally independent of Froude number in the early stage of water entry. However, discrepancies in profiles gradually appear at a later time. For the airflow characteristics, circumferential vortex rings are found near the free surface in the early stage of water entry. The pressure inside the cavity decreases with time because of the rapid growth in cavity volume, which the entrained air cannot compensate for.