Non-linear Transient Rotor-dynamics Analysis Of Fan Blade Out

Aero-engines work in the environment with high temperature,high pressure and complex vibration through whole life.The position of stress concentration would yield plastic deformation caused by long-time and alternate stress.Similarly,a FBO event may be caused by impact damage by foreign objects such as bird strike.Ballistic impact,high non-linear dynamics and rotor dynamics are involved in FBO research.And FBO research always is the hot spot in aircraft non-linear dynamic.The potential damage by FBO happens in two stages.Firstly,the released blade will impact the fan case.A released blade may interact with remaining blades and result in further damage.A larege mounts of finite element simulation and small experiments have be investigated.Secondly,the sudden unbalance upon FBO will force the Fan rotor vibrate highly.So that tips of contained blades may interact with the fan case.The paper focus on the second stage to analyse transient response of rotor system after FBO.The fan blade is remained to do transient dynamical analysis.We divided the procedure into three parts.Firstly,critical speed and transient unbalance response analysis of various cross-section shaft with multi-supports have been done.Functional equations of mode shapes drived are used to analyse transient dynamics by using Galerkin method.Secondly,non-linear dynamical equations coupled axial and lateral motions of fan blade tip subjected impact are derived and load at root of blade is obtained.During the process of derivation,Coriolis force and centrifugal force are involved.Transient response of fan blade with constent and varying rotate speed has been finished.Finally,combine dynamical equations of varying section shaft with fan blades subjected impact to analyze transient response after FBO.The sudden unbalance force will force rotor rotate in an eccentric path.Tips of the remaining blades may come in contacted with fan case.The impact force between fan blade and case is determined by transverse vibration of hub.According to the load,vibration and force at root can be obtained.Longitudinal force after vector synthesis determines the transverse vibration of shaft.Lateral force multiply radius of hub influences the rotate speed.Finally,whirl of shaft and impact vibration of fan blade iterated and mutual controlled contributes to transient response.Theoretical model to analyse the FBO event or blades rubing with case is established.Changing parameters according to different aeroengine to calculate transient response and give theoretical reference of rotor rubbing diagnosis.