Whole-assembly flutter analysis of a low-pressure turbine blade

This paper reports the findings of a flutter investigation on a low-pressur e turbine blade using a 3D, non-linear, integrated aeroelasticity method. T he approach has two important features: (i) the calculations are performed in a time-accurate and integrated fashion, whereby the structural and fluid domains are linked via an exchange of boundary conditions at each time ste p, and (ii) the analysis is performed on the entire bladed-disk assembly, t hus removing the need to assume a critical vibration mode shape. Although s uch calculations are both CPU and in-core memory intensive, they do not req uire prior knowledge of the flutter mode and hence allow a better understan ding of the aeroelasticity phenomena involved. The flow is modelled inviscidly but the steady-state viscous effects are ac counted for using a distributed loss model. The structural model was obtain ed from a standard finite element (FE) representation and a large number of assembly modes were included in the calculations. The study focused on thr ee part-speed conditions at which a number of unstable modes were known to exist from the available experimental data. The whole assembly was modelled using about 664,000 mesh points and predictions were made of aeroelastic m odal time histories. From these time histories it was possible to identify the forward and backward travelling waves and to deduce the unstable modes of vibration. The theoretical predictions were found to be in very good agr eement with the experimental findings.