School of Astronautics, Harbin Institute of Technology, Harbin, 150001, China.
Sci Rep. 2023 Jan 20;13(1):1153. doi: 10.1038/s41598-023-27922-8.
The internal structure of many aero-engines is designed with a dual-rotor system. Up to now, there have been few studies on the influence of aerodynamic excitation on the dual-rotor system. The phenomenon of synchronous impact may occur when the frequency of the aerodynamic excitation force of the fan blade is close to the characteristic frequency of the inter-shaft bearing. This paper investigates the dynamic characteristics of a dual-rotor system under the condition of synchronous impact. The system's motion equations are formulated considering the complex nonlinearities of the inter-shaft bearing, such as Hertz contact force of 10/9 exponential function, clearance, and periodic varying compliance. In addition, the inter-shaft bearing with a local defect is considered. The fan blade's aerodynamic excitation force is modeled by synthesizing multiple harmonic excitation forces, the amplitudes of which are obtained by the Fourier series expansion. Numerical simulations are employed to get the dynamic responses of the system. The results show that the dynamic characteristic of the dual-rotor system at the primary resonance caused by the high-pressure (H.P.) rotor is not changed by the aerodynamic excitation force, while the primary resonance caused by the low-pressure (L.P.) rotor increases significantly. However, three aerodynamic resonances of the amplitude-frequency response of the dual-rotor system are emerging in the low-frequency region (124, 146 and 186 rad/s). When the synchronous impact phenomenon occurs, the amplitude of the three resonance peaks will increase twice compared to the original status, leading to a doubled increase in the dynamic load of the inter-shaft bearing. The characteristics of the dual-rotor system affected by the parameters such as initial phase difference of local defect, rotor eccentricity of system, clearance of inter-shaft bearing, and the stiffness and damping of supports are discussed in detail. The results obtained provide a deep insight into the mechanism of synchronous impact.
许多航空发动机的内部结构采用双转子系统设计。迄今为止，关于气动激励对双转子系统的影响的研究还很少。当风扇叶片的气动激励力频率接近轴间轴承的特征频率时，可能会发生同步冲击现象。本文研究了同步冲击条件下双转子系统的动态特性。考虑到轴间轴承的复杂非线性，如赫兹接触力的 10/9 指数函数、间隙和周期变化的柔度，建立了系统的运动方程。此外，还考虑了带有局部缺陷的轴间轴承。风扇叶片的气动激励力通过综合多个谐波激励力来建模，其幅值通过傅里叶级数展开获得。采用数值模拟方法得到系统的动态响应。结果表明，由高压（H.P.）转子引起的系统主共振的动态特性不受气动激励力的影响，而由低压（L.P.）转子引起的主共振显著增加。然而，双转子系统的幅频响应出现了三个气动共振，频率在低频区（124、146 和 186 rad/s）。当发生同步冲击现象时，三个共振峰值的振幅将比原始状态增加两倍，导致轴间轴承的动载荷增加一倍。详细讨论了局部缺陷初始相位差、系统转子偏心、轴间轴承间隙、支撑的刚度和阻尼等参数对双转子系统特性的影响。研究结果为同步冲击的机理提供了深入的了解。
