Air-water coupling effect and motion response characteristics of seaplane during takeoff and landing process

To investigate the effects of air-water coupling on motion response of seaplane in wave environment during the takeoff and landing process, a scaled model of seaplane was used as the research object. The numerical simulation method of air-liquid two-phase flow coupling was established based on the background domain global dynamic mesh and overset mesh method, SST k-ω model, VOF free surface model, and DFBI six-degree-of-freedom model. Firstly, the accuracy of this numerical method was verified by comparing the results of static water experiments. Then, the air-water coupling and motion response characteristics of seaplane during the takeoff and landing process in still water and wave environment (wave length 5 m, wave height 0.07 m) were numerically studied. The research shows that air-water coupling effects during the movement of seaplane are mainly reflected in the evolution characteristics of flow field pressure distribution, contact timing and load response. The takeoff process is divided into three phases: accelerated taxiing, high-speed skipping, and takeoff. The air-water coupling effects exhibit three-phase characteristics with velocity. The hydrodynamic force is dominant in the low-speed taxiing phase. Hydrodynamic and aerodynamic forces coupling effects work together in medium-speed phase. The aerodynamic force is dominant in the high-speed skipping phase. Additionally, during this phase, the instability of the pitch moment caused by vortex shedding in the wing wake exacerbates the hydrodynamic and aerodynamic force coupling fluctuations. During the landing process, the initial vertical load upon first contact with water was 4g in still water environment, with a high-medium-low pressure gradient observed amidships. In the high-speed skipping phase, due to different parts of the fuselage contacting the water sequentially, both horizontal resistance and vertical load exhibited double peaks. In wave environment, the first contact with water occurred near the wave ascent area, and the vertical load of 6.5g, an increase of 62.5% compared to that in still water. In the skipping phase, the wave buffering effects are formed due to multiple small impacts. The maximum vertical load is only 1.88g. The impact load is effectively reduced. This study reveals the influence of air-water coupling effects on the motion characteristics of seaplane in different conditions and phases, providing methods and data support for its performance optimization in complex environments.