Fluid flow behaviors of the truncated trimaran model entering into water with various heel angles

During water entry, air bubbles are usually trapped under a wet deck. At present, the deformation and escape process of bubbles under vertical water entry are understood. However, the asymmetric flow characteristics of bubbles in oblique postures are still poorly understood. In this work, experimental and numerical methods are used to investigate these flow characteristics. Through the constructed dimensionless system, the bubble flow and load similarity behavior in the oblique postures are discovered. Combined with the experimental data, the flow on the free surface under oblique water entry was investigated, and the evolution of the bubbles on the left and right sides was determined to be asynchronous. The correspondence between the structural motion and slamming force was further analyzed. The movement behavior of the trimaran was affected by asynchronous slamming on the left and right sides, and it went through three key stages: gravity dominance, slamming deceleration, and dynamic equilibrium. The current volume of fluid method can accurately capture bubble generation and deformation. However, in the later stage of the simulation, a nonphysical merging phenomenon may occur in the bubble expansion and fragmentation stages. Finally, the bubble flow patterns and loading behaviors under varying impact velocity conditions are analyzed. This shows that at the peak moment, the bubble volume decreases as the impact velocity increases, but this effect does not affect the dimensionless pressure coefficient. Understanding this equivalent behavior will be helpful for the load conversion of real ships under various water impact conditions.