Fan supersonic flutter prediction and test analysis

Abstract

The subject is introduced by describing the aerodynamic and vibration characteristics of unstalled, supersonic flutter in fan assemblies having part-span shrouds or clappers. It is briefly compared and contrasted with stall flutter. The importance of frequency and modeshape analyses is stressed and supersonic flutter prediction methods are examined, commencing with the modeshape parameter CO/H. Unsteady work theory leads to the study of aerodynamic damping with the prediction of flutter mode, speed and wave direction. Throughout, emphasis is given to the support of design analysis by test data, from laboratory measurements on stationary models to full scale engine Altitude Test Chamber behaviour. Finally, the effect on flutter of some of the operating criteria in engine service is considered.