Abstract:

Blended Wing Body （BWB） layout is one of the important layouts for future civil aircraft. The influence of initial speed and pitch angle on the motion characteristics of BWB aircraft during ditching at a fixed glide angle is studied by numerical simulation. The finite volume method is used to solve the unsteady RANS equations， the volume of fluid method is used to capture the water-air interface， the rigid body six-degree-of-freedom model is adopted to couple the force and motion of the aircraft， and the global moving mesh method is applied to realize the relative motion between the aircraft and the water surface. In the phase plane of the initial ditching horizontal speed and pitch angle， three forms of motion for BWB aircraft are observed during the process of ditching： stable motion， porpoising motion， and skipping motion. With the increase of initial ditching speed or pitch angle， the aircraft gradually transitions from stable motion to porpoising motion and finally to skipping motion. When the initial ditching horizontal speed increases， the absolute value and range of the pressure in the positive pressure zone formed by the impact and the negative pressure zone formed by the hydroplaning increase. When the positive and negative pressure zones are located before and after the center of gravity， respectively， they jointly lead to a pitch-up moment peak. When the initial ditching vertical speed increases， the aircraft rebounds to a higher position after water entry. When the initial ditching pitch angle increases， the initial center of gravity position rises， and the growth of wetted area at the initial stage in ditching slows down， both jointly leading to an increase in water entry depth and a forward movement of the waterline.

Key words: ditching, blended wing body (BWB), porpoising motion, skipping motion, numerical simulation