A Framework for Flutter Clearance of Aeroengine Blades

Abstract

A framework for flutter operability assessment, based upon a new set of similarity parameters, has been developed. This set consists of four parameters which embrace both the performance characteristics in terms of corrected mass flow and corrected speed, and the flight condition in terms of inlet temperature and density (or, equivalently, inlet pressure). It is shown that a combined mass-damping parameter, g/ρ*, novel in the field of turbomachinery aeroelasticity, can summarize the individual effects of mechanical damping, g, and blade mass ratio, μ. A particular selection of four nondimensional parameters, including g/ρ* and a compressible reduced frequency parameter, K*, allows for a decoupling of corrected performance effects from purely aeroelastic effects, for a given machine and a specific modeshape. This view of flutter operability is applied to the analysis of full-scale engine data. The data exhibits the trend that increasing K* and increasing g/ρ* have stabilizing effects, which is consistent with previous work in flutter stability. We propose that these trends hold generally, and apply the trends towards constructing a flutter clearance methodology, a test procedure which satisfies the requirements for comprehensive flutter stability testing.