Linearized flutter investigations of mistuned turbomachinery blading

Abstract

Linear aerodynamic investigations for unsteady turbomachinery applications - mainly time-linearized and time-sprectral methods - are evaluated with respect to physics quality and computational efficiency. The aeroelastic stability of several compressor test cases is examined through code-to-code comparison and through validation with non-linear simulations as well as with experimental data. Based on these fast aerodynamic approaches a detailed sensitivity analysis is performed on an actual flutter case to review different stabilization strategies. Aeroelastic similarity parameters are varied and perturbations of the mode shape are considered in order to derive rules for flutter-free design. In this context an aeroelastic reduced order model in the state space, AEturbo by name, is presented. It enables the flutter analysis of rotationally non-symmetric rotor configurations, either in terms of frequency mistuning or due to aerodynamic asymmetries. Moreover the design tool facilitates the assessment of mode family coupling and is capable of model updating via experimental modal analysis of a blisk. The funtcionality of AEturbo is demonstrated by means of the DLR ultra high bypass ratio fan, a modern transonic fan stage that will soon be subject to a rig-test.