Advances in fan and compressor blade flutter analysis and predictions

Abstract

A unified approach to flutter prediction has been developed at Pratt & Whitney Aircraft (P&WA). The aeromechanical stability of the blade-disk system is expressed in terms of a stability parameter which measures the amount of unsteady work done by the air on the system, when the system is vibrating in one of its natural modes. In neutrally stable systems, the unsteady work done by the air on the blades will balance the work dissipated by friction and by material damping. An accurate prediction of the vibrational deflections and of the unsteady aerodynamic forces is required at every spanwise location on each blade, so that the work done by the unsteady aerodynamic forces may be calculated. Recent progress is described in the prediction of unsteady aerodynamic forces and the determination of mode shapes. The stability model is applied to the prediction of supersonic flutter, chord wise bending flutter, and stall flutter. Recommendations are made for additional work necessary to improve the prediction model.