Research On Sustained Imbalance Vibration Of Fan Rotor In High Bypass Ratio Turbofan Engine

AC25-24 "Sustained Engine Imbalance" requires that,the engine structural model needs to be established for the problem of sustained vibration of the engine caused by Fan Blade Out events.However,due to the fact that the Sustained unbalanced state deviates from the design point and the working conditions are complex and usually involves nonlinear problems such as rubbing,it is difficult to select appropriate parameters and modeling methods when building the engine structural model.In this paper,the vibration characteristics of a large bypass ratio turbofan engine fan rotor in sustained unbalanced state are studied in order to provide certain reference and support for the airworthiness certification and validation of the domestic new type aero-engine.In this paper,a fan blade model is established based on the relevant fan blade sizes of a typical commercial high bypass ratio turbofan engine,and vibration stress analysis is performed.The results show that the resonance margin of the fan blade meets the requirements;according to the typical fan-rotor structure of a commercial large bypass ratio turbofan engine,a fan rotor model is established to obtain the first two critical speeds of the fan rotor;comparison between the experimental results of the rotor test rig and the finite element simulation results shows that the finite element modeling method for the low pressure rotor is correct and feasible;based on the size of a typical commercial high bypass ratio turbofan engine,an engine size model is established to perform dynamics analysis.Under the Fan Blade Out and the rotor-stator is not rubbed,study the vibration characteristics of the fan rotor under sustained unbalanced conditions,analyze the influence of rotational speed and severity of fan blade out on the unbalance response of the fan rotor.The results show that: the vibration amplitude of the fan rotor is larger when the rotation speed is closer to the critical rotation speed of the fan rotor and the unbalance is larger;and the vibration response of the fan rotor is only one frequency multiplication under the conditions of different rotation speeds and unbalances.Under the Fan Blade Out and the rotor-stator is not rubbed,study the vibration characteristics of the fan rotor under sustained unbalanced conditions,analyze the influence of windmill speed?clearance and materials of rotor and stator?severity of fan blade out?rotor speed drop rate on unbalanced response of fan rotor.The results show that: The results show that the greater the speed of the windmill,the smaller the gap between fan rotor and casing,the greater the stiffness of the material,the more serious the blade out,the greater the impact of rubbing on the response of the fan rotor,the more pronounced the non-linearity of the unbalanced response of the fan rotor;the rate of decrease of the rotor speed will not affect the maximum amplitude of the unbalanced response of the fan rotor,but it will affect the time to reach the maximum amplitude.When the rub-impact degree is lighter,the frequency components of the rub-impact fault are prone to X/2 frequency division components in addition to the frequency multiplication component;when the rub-impact degree is lighter,the frequency components of the rub-impact fault are prone to X/4 frequency division components in addition to the frequency multiplication component.