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在研究某两种型号航空发动机振动的过程中,作者曾对数十台发动机的振动信号做过实时数字分析。分析结果表明,其中相当多台份在工作转速范围内存在自动跟踪的精确1/2阶非协调进动,并且常常是使该发动机振动较大的主要原因。文中介绍了这种非协调进动的表现特征及典型的数字分析结果。本文对产生非协调进动的原因作了具体分析,初步归结为套齿联轴器中的内摩擦,叶尖间隙的气动弹性,滚动轴承的非线性刚性,以及后支承非线性刚性等因素。导出了在这些因素联合作用下悬臂式转子运动的四个非线性微分方程。结合具体结构参数,在模拟计算机及数字计算机上作了大量的运算。研究结果表明:在这些因素的联合作用下,使处于超临界工作状态的悬臂式低压涡轮转子产生自激。由于激起的进动频率接近为1/2转速,因分谐波共振就形成了自动跟踪精确1/2阶非协调进动。套齿联轴器内的摩擦力矩是首要的自激因素,后支承的非对称、非线性刚性则是形成自动跟踪1/2阶分谐波振动的主要原因。文章还提出了在不改变发动机结构情况下所可能采取的排振措施。
In studying the vibrations of two types of aero-engines, the author conducted real-time numerical analyzes of the vibration signals of dozens of engines. The analysis results show that quite a few of them have accurate ½-step non-coordinated precession of automatic tracking within the working speed range, and often cause the larger vibration of the engine. The paper presents the performance characteristics of this non-coordinated precession and the typical numerical analysis results. This paper gives a detailed analysis of the causes of non-coordinated precession, which is mainly attributed to the internal friction in the sleeve coupling, the aeroelasticity of the tip clearance, the nonlinear stiffness of the rolling bearing and the nonlinear stiffness of the back support. The four nonlinear differential equations of cantilever rotor motion under the combined action of these factors are derived. Combined with the specific structural parameters, a large number of calculations have been made on analog computers and digital computers. The results show that under the combined action of these factors, the cantilever low-pressure turbine rotor in the supercritical state is self-excited. As excited precession frequency close to 1/2 speed, subharmonic resonance formed on the automatic tracking of accurate 1/2 order non-coordinated precession. The friction torque in the coupling gear is the primary self-excitation factor. The asymmetry and the non-linear stiffness of the back support are the main reasons for the automatic tracking of 1/2 subharmonic vibration. The paper also proposes the possible measures of vibration reduction without changing the structure of the engine.