This work presents a numerical study of the water-exit characteristics of a bioinspired unmanned aerial-underwater vehicle (UAUV) equipped with a front-mounted propeller. A robust solution framework was established on the basis of a modified Shear Stress Transport (SST) turbulence model, volume of fluid (VOF) multiphase formulation, overset grid technique, and six degrees of freedom (6-DOF) motion model; the framework was verified against a canonical water-exit case of a sphere. Inspired by the morphology and water-exit behavior of flying fish, a bioinspired three-dimensional (3D) model was designed. Using this framework, the effects of the front-mounted propeller configuration, exit velocity, and exit angle were examined; the exit process under different conditions was analyzed; and the relationship between exit drag and exit state was quantified. The results demonstrate that the proposed approach can resolve the water-exit performance of the bioinspired UAUV in detail. Folding the front-mounted propeller effectively reduces exit drag and mitigates high-pressure concentrations on the blades. When the exit velocity is ≥8 m/s and the exit angle θ ≤ 30°, the peak exit drag does not surpass 90.004 N. The peak exit drag exhibits a pronounced quadratic relationship with both exit velocity and exit angle. To ensure safe water exit, the UAUV should avoid exiting with the front-mounted propeller deployed and avoid excessively low exit velocities and overly large exit angles. The numerical investigation of exit drag provides effective bioinspired design guidelines and a feasible analysis strategy for UAUV development. In conclusion, the findings provide crucial insights for designing more efficient bioinspired UAUVs, particularly in terms of minimizing water-exit drag and optimizing the configuration of the 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.