| Abstract: | To enhance the understanding of design characters,which have prominent influences during the fan blade out event,a simplified geometrical and dynamic analysis method was derived,and a typical 2-shaft high bypass ratio turbofan engine was selected and modeled.Based on analytical deriving and engineering experience learned from the real engine failure case,three determinative impact actions were recognized from the fan blade out process.The transient trajectories of these impact actions were researched in analytical method,and then thickness of acoustic lining,quantity of fan blades and threshold load of structural fuse were analyzed as key design characters.36 serialized fan blade out transient dynamic simulations were conducted by using the 2-shaft high bypass ratio turbofan engine model within different combinations of the three key design factors.The results from geometrical and dynamic analysis matched mainly well with the results from simulations.Characteristic phenomenon in simulation can be explained theoretically.Five conclusions can be summarized from these results.(1) If thickness fan acoustic lining was thinner,the deviation between simplified analytical calculation and simulation were not outstanding to predict Blade-Casing the first impact time and angular position.(2) An appropriate thickness of acoustic lining could make a lower impact stress of fan casing at the first impact.(3)Different thickness of acoustic linings leaded to two impact modes for blade 2,which were tip impact and root impact.(4) Different impact conditions between blade 1 and blade 2 caused remarkable speed components distinction of blade 1,and leaded to a wide range of transient trajectory of blade 1 during FBO event.(5) Thicker acoustic lining in this research can usually find the porper threshold loads setting,which can give a satisfactory outbound vibration.Two details were raised for further research,which were impact behavior of composite material fan blade and honeycomb and influences of wider FBO threshold load ranges in design cases with thinner acoustic lining. |
