Computational simulation of an unmanned air vehicle impacting water

Abstract

Computational simulations were performed to study the splashdown of an unmanned air vehicle (UAV) falling nose-first into seawater from various heights. Solutions were generated with a time-accurate finite-volume method based on the unsteady compressible ensemble averaged Navier-Stokes equations for the air and the unsteady incompressible ensemble averaged Navier-Stokes equations for the seawater. The volume of fluid model was used to track the air-water interface and a deforming mesh algorithm was used to move the UAV through the computational domain. Computed pressure histories at four key locations on the UAV forebody were compared with experimentally measured values to validate this study. The computational simulations were shown to have accurately predicted the magnitude and character of the pressure histories, but with some discrepancies in the behavior of the pressure within the UAV inlet aperture. Results are presented for various drop heights, which simulated a range of impact velocities. Modifications were also made to the UAV geometry to examine the effect of deflecting the upper inlet lip downward. Deflection angles of 30 deg and 20 deg were analyzed for a drop height condition of 35 ft with results showing a significant decrease in impact force and pressure within the inlet.