A Fan Blade-Flexible Casing Rubbing Dynamic Model and Its Application

To support the airworthiness certification of aircraft engines regarding CCAR 33.63 provisions, a three-dimensional contact dynamics-based computational model for fan blade-flexible casing rubbing vibration was established. Modal reduction was employed to reduce the size of the computational model, while a cubic B-spline surface fitting technique was utilized to enhance the discretization accuracy of the casing inner surface. A bilinear elastic-plastic model was adopted to describe the rubbing mechanical properties of the abradable coating, and contact forces between blades and casings were calculated based on coating wear depth, blade thickness, and element shape functions. Using this model, the rubbing response characteristics between fan blades and flexible casings were investigated. The results showed that blade damping is a key factor affecting rubbing vibration response. For blades with lower damping, in addition to coupling vibrations between blade-casing single nodal diameter modes during rubbing process, there also exist blade-casing coupled vibrations caused by traveling waves associated with multi-nodal diameter modes of casings. The variations in contact strength during rubbing process leading to changes in dynamic characteristics of components cause the above interactions. The dynamic model established in this paper provides a new approach for identifying and evaluating blade-casing rubbing coupled vibrations.