Numerical study on the water-entry impact characteristics of a bionic unmanned aerial-underwater vehicle with front-mounted propeller

This study numerically analyzed the impact characteristics of a biologically inspired unmanned aerial-underwater vehicle (UAUV) with a front-mounted propeller during water entry. Using the modified Shear-Stress Transport (SST) turbulence model, Volume of fluid (VOF) model, overset grid method, and six-degrees-of-freedom (6-DOF) motion model, a robust numerical solution approach was developed and validated using benchmark cases of conical and hemispherical bodies water entry. The design of the three-dimensional (3D) bionic UAUV was motivated by analyzing the unique morphology and diving behavior of flying fish. The proposed numerical method was then used to investigate the effects of the front-mounted propeller, water-entry velocity, and water-entry angle on the impact characteristics of the UAUV. The correlation between entry parameters and resulting impact acceleration was assessed through analysis of various water-entry scenarios. The results demonstrate that the numerical approach effectively captures the detailed impact characteristics of the bionic UAUV. Folding the front-mounted propeller significantly reduces water-entry resistance and mitigates localized high-pressure zones on the blades. Under entry velocities of 10 m/s or lower and angles not exceeding 30°, the peak impact acceleration does not surpass 2.27 g. Maximum impact acceleration exhibits a quadratic relationship with entry velocity and a quartic relationship with entry angle. To minimize the risk of structural damage during water entry, the UAUV should avoid entering with an unfolded front propeller, excessively high water-entry speeds, or steep angles. This study offers a practical bionic design reference and an effective strategy for UAUV design and water-entry impact analysis.