Modelling of Trailing Edge Flow Tones in Elastic Structures

Abstract

The hydroelastic coupling of turbine blade vibration modes and trailing edge vortex shedding from the blade is a well known phenomenon that leads to intense audible tones and shortened fatigue life. Historically, most researches on such turbo-blade “singing” have focussed on the prediction of the vortex shedding frequency and on the reduction of offending vibration levels by reshaping the trailing edges. The associated control measures effectively permit the “detuning” of the vortex shedding from the blade modes, and the effectiveness of such measures is more or less qualitatively known. This paper builds on and extends a different line of research that is aimed at merging the controling fluid dynamic and structural dynamic factors of these flow-induced tones into a quantitative semiempirical model of the non linear flow-induced vibration of turbo machine blading. The elements of the model development involve the use of measured nonlinear “wake impedances” by the forced motion of trailing edges, the development of a mathematical model for the response of blade structures that are coupled to the wake dynamics, and finally the testing of the modeling against measured flow-induced vibration of simple hydrofoils. The parameters used in both the modeling and the experimental verification include structure mass density, hydrofoil geometry, damping, and trailing edge geometry.