Experimental Validation of Numerical Blade Flutter Prediction

Abstract

Blade flutter of modern gas-turbine engines is one of the main issues that engine designers have to face. The most used numerical method that is employed for flutter prediction is the energy method. Although a lot of papers are devoted to the analysis of different blade wheels, this method was rarely validated by experiments. Typical mesh size, time step, and various modeling approaches that guarantee reliable flutter prediction are not commonly known, whereas some examples show that predictions obtained through nonvalidated codes can be inaccurate. In this paper, we describe our implementation of the energy method. Analysis of convergence and sensitivity to various modeling abstractions are carefully investigated. Numerical results are verified by compressor and full engine flutter test data. It is shown that the prediction of flutter onset is rather reliable so that the modeling approaches presented in this paper can be used by other researchers for the flutter analysis of industrial compressor blades. Nomenclature f = natural frequency m = number of nodal diameters N = number of blades n = rotor speed W = work done by the unsteady pressure over one cycle of blade oscillation α = inlet angle of attack φ = 2π m∕N, interblade phase shift ω = 2πf, circular frequency

Effects of a Single Blade Incidence Angle Offset on Adjacent Blades in a Linear Cascade

“…Aerodynamic unsteady pressure loading of a blade during a certain part of the oscillatory cycle contributes to a rising damping force and to its suppression. Without accurate knowledge of the resulting excitation load variation over time, it is impossible to affirm that the blade will continue to flutter after the initial deflection [16]. As the excitation force and moment are not known during the blade design cycle, it is not always possible to construct flutter-resistant blades.…”