PREDICTION OF TURBOFAN VIBRATIONS VIA DISTINCT WAVES

摘要

Excitation frequency approaching a "split peak" causes only one blade in a shroudless fan - the "rogue blade" - to respond in the full resonant condition, as revealed through extension of previously published inter-transformable coordinate systems, which enable formulation of elliptical whirl in a whole engine as distinct waves to encompass nonuniform blade flexing. A plan for step-by-step, physics-based computations to predict critical vibratory stresses in the "rogue blade", disk and fan shaft due to inlet flow distortion and/or engine whirl, given a specific distribution of blades with individually predetermined response as applicable in the step and as varying with axial slope and displacement at the root, is advanced. The analysis correlates with Campbell's 1924 experimental results. The mechanism through which nonuniformity actually reduces potential nonsynchronous vibratory stresses in a fan with an interlocked part-span shroud is examined through experimental evidence secured during investigation of a 1989 airline crash.