The unmanned aerial–underwater vehicle (UAUV) is a new type of vehicle that can fly in the air and cruise in water and is expected to cross the free water surface several times to perform continuous uninterrupted observation and sampling. To analyze the hydrodynamic and motion characteristics of the vehicle, the whole water-entry process of a multi-degree-of-freedom UAUV with various velocity and pitch angle was investigated through a Reynolds-averaged Navier–Stokes method. The computational domain was meshed by trimmer cells. The relative movement between the vehicle and fluid domain was simulated using moving reference frame overset mesh to delineate the interaction region around vehicle body. To reduce the computational cost, adaptive mesh refinement and adaptive time-stepping strategy were used to capture the slamming pressure accurately with reasonable computational effort. First, convergence study is considered. Simulations of the vehicle with various initial velocities and different pitch angles were performed. The variable physical properties were analyzed, and detailed results through the time-varying force and velocity were shown. Initial velocity and pitch angle are found to significantly influence hydrodynamic behavior, including the time-varying force, while thickness ratio has a great impact on added mass and pressure. The results show that higher entry velocity results in greater peak vertical force. The transverse hydrodynamic characteristics for oblique water entry of the vehicle with varies pith angle are quite different.

Unmanned aerial underwater vehicles (UAUVs) will play significant roles in several complex application scenarios including observation of mesoscale ocean phenomena, monitoring of offshore platforms, ocean protection, and maritime rescue. These innovative vehicles can be used in the air and underwater and can easily enter and exit water. This review systematically analyzes the research progress, design challenges, and future prospects of UAUVs, emphasizing their potential to revolutionize integrated cross-domain collaboration. We classify UAUVs into five categories—rotary-wing, fixed-wing, folding-wing, hybrid-wing, and flapping-wing—based on propulsion configurations, and critically evaluate their prototypes, highlighting technological milestones and functional limitations. Unlike prior reviews focused solely on technical developments, this study advocates for a paradigm shift from a technology-push to a market-pull and technology-push interactive development model. Combining the design of UAUV with solutions to technical challenges and specific application requirements is crucial for practical deployment. By synthesizing historical context, current advancements, and future developments, this review not only provides possible strategies for design challenges but also lays a roadmap for UAUV commercialization.