Vibrational Transfer Path Analysis And Vibration Isolation Of Turboshaft Engine With Mounted Conditions

The engine which is the main source causing vibration and noise of the helicopter, now is the research focus of helicopter-engine integrated design since the vibration level of the helicopter is the main factor that affects the security, comfort and life of the whole system and the reliability of the equipment and instruments. Generally speaking, only the transverse vibration, mainly caused by the unbalance excitation force of the rotor of the engine, has a significant impact on the helicopter. In this paper, the problem of vibration transmission of the helicopter with an unbalanced excitation of the rotor is the focus. According to the transfer path analysis(TPA) method, the vibration transmission of the simplified model of the turboshaft engine was analyzed, vibration response of every target point on the engine mounting system was predicted and vibration contribution of every transmission path was analyzed. At the same time, vibration isolation method of the mounting system of the turboshaft engine was analyzed and evaluated based on the load identification results of TPA. The main work and conclusions are as follows:(1)The typical structure of the support system and the mounting system of the turboshaft engine was analyzed. A simplified model of the turboshaft engine with a single rotor and its mounting system was designed and vibration transfer paths of the test model were analyzed. The results show that: The mounting system can be approximated as a parallel spring-damper system. Load of every transfer path consists mostly of the fundamental frequency excitation while double frequency excitation has a secondary effect and the excitation of other frequencies is relatively small. The total vibration response obtained by the traditional TPA method is in good agreement with the actual results.(2)The vibration contribution of every transfer path was analyzed according to the contribution plot of every transfer path and the vector overlay graphs of vibration contribution. The results show that: For the mounting system with a redundant bar, the dominant factors which have effects on vibration response of target points include transmission characteristic of the whole system and the exciting force of rotor. For the mounting system without the redundant bar, the dominant factor which has effects on vibration response of target points is the unbalanced excitation force of rotor, which needs to carry out a dynamic balance test of the rotor.(3)According to technical requirements and the existing vibration isolators used in the mounting system of the engine, the high damping silicone rubber vibration isolator is a good option. For the mounting system with a redundant bar, modal analysis and vibration response analysis were carried out based on the load identification results of TPA. The results show that simulation results of axial vibration response of slant beams except the redundant bar is in good agreement with the test which verified the reliability of the simulation model. According to vibration attenuation mechanism, parameter design of the vibration isolators used in joints between slant beams and the casing was carried out based on finite element method which determined the influence of spring constant and damping coefficient on the isolation coefficient.