共轴式直升机地面共振机理分析

Physical mechanism investigation of coaxial helicopter ground resonance

为理解共轴式直升机上下旋翼与机体之间的耦合作用,提出了一种分析共轴式直升机地面共振物理机理的时-频分析方法。考虑上下旋翼周期型摆振与机体俯仰和滚转自由度(DOF),建立了具有结构阻尼的共轴铰接式旋翼直升机地面共振分析模型。通过特征值计算和扰动运动方程的数值积分,获得了共轴式直升机地面共振的模态特性及时域响应特性,根据各自由度的响应特性揭示了旋翼与机体之间的相互作用。分析表明,具有上旋翼特征的摆振后退型模态是最不稳定模态。在动不稳定区内,上旋翼周期摆振与机体滚转自由度之间相互输入能量,是造成共轴式直升机地面共振的主要原因;对于该不稳定模态,下旋翼的周期摆振与机体滚转自由度之间也构成相互输入能量的相位关系,增加了直升机地面共振的动不稳定性。

In order to understand the coupling interaction between upper/lower rotor and fuselage of coaxial helicopter, a time-frequency analytical method is presented to analyze physical mechanism of coaxial helicopter ground resonance. An analytical model for coaxial articulated rotor helicopter ground resonance with structural damping is established, considering periodic lag motion DOFs （upper rotor and lower rotor）, body pitch rotation DOF and body roll rotation DOF. Eigenvalue calculation and numerical integration of disturbance equations of motions are used to obtain modal characteristics and time- domain response characteristics of coaxial helicopter ground resonance, and the interaction between rotors and body is revealed according to the response of various DOFs. The analytical results show that regressive lag mode with upper rotor characteristics is the most instability mode. In dynamic instability region, coaxial helicopter ground resonance is mainly due to energy transferred between periodic lag motion of upper rotor and body roll rotation. For this instability mode, energy transferred between periodic lag motion of lower rotor and body roll rotation also exists and it can enhance ground resonance instability of coaxial helicopter.