基于重叠网格法的飞机水上降落水动力砰击载荷研究

为分析飞机在水上降落过程中的砰击载荷及运动规律,基于数值模拟研究NACA TN2929飞机水上降落过程,考查飞机的初始速度、初始仰角对降落过程的影响。求解雷诺平均纳维-斯托克斯方程(RANS)模拟飞机与水的相互作用,采用VOF方法捕捉自由面,采用重叠网格技术及DFBI模型模拟飞机与流体的耦合运动。通过计算楔形体和圆锥体自由入水过程验证模型的可靠性,通过网格和时间步长的收敛性分析确定合适的网格和时间步大小,与实验结果对比确定计算结果的正确性。模拟飞机以不同初始速度与不同仰角的着水过程,分析飞机底部压力的变化规律,研究飞机初始速度、初始仰角对砰击载荷及运动姿态的影响规律。数值计算结果表明飞机在入水0.2 s左右砰击载荷会达到峰值,载荷峰值与飞机着水的速度的平方线性相关;飞机机身底部压力峰值出现在水面与机身的正向交界处;飞机初始仰角增加,砰击载荷峰值会有所减小。

Identification of hydrodynamic impact loads during the airplane ditching-based on overset grid method

In order to analyse the impact load and motion of an airplane during ditching, the ditching process of NACA TN2929 on the water was investigated by numerical simulations.The ditching strategy with various speed and pitch angle was concerned.The interactions between the airplane and water surface were simulated through solving the reynolds averaged navier-stokes(RANS) equations.The volume of Fluid(VOF) mothed was used to simulate the free surface.The overset grid method with dynamic fluid body interaction(DFBI) module was introduced to solve the coupled motion.The free fall water entry of a wedge and a cone was simulated.The convergence studies on the mesh size and time resolution for the analysis of airplane ditching were carried out and the results were further validated through comparing with the experimental data.Simulations of the airplane with different ditching velocities and various pitch angles were performed.The pressure distributions, the impact loads and the motion of the aeroplane were analysed.It is found the slamming load will reach a peak at 0.2 s after entering the water.The peak pressure at the bottom of the fuselage appears at the intersection of the free surface and the fuselage.The peak load is linearly related to the square of the landing speed.As the initial pitch angle increases, the peak slamming load will decrease slightly.