Whole-assembly flutter analysis of a low pressure turbine blade

This paper reports the findings of a flutter investigation on a low pressure turbine blade using a 3D non-linear integrated aeroelasticity method. The 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 step, and (ii) the analysis is performed on the entire bladed-disk assembly, thus removing the need to assume a critical interblade phase angle. Although such calculations are both CPU and in-core memory intensive, they do not require pre-knowledge of the flutter mode and hence they allow a better understanding of the aeroelasticity phenomena involved. The flow is modelled inviscidly but the steady-state viscous effects are accounted for using a distributed loss model. The structural model was obtained from a standard FE eigensolution and a large number of assembly modes were included in the calculations. The study was focused on a part-speed condition at which a number of unstable modes were known to exist from the available experimental data. The whole assembly was modelled using about 650,000 nodal points and predictions were made of aeroelastic modal time histories. From those time histories, it was possible to identify the forward and backward traveling waves and to deduce the unstable modes of vibration. The theoretical predictions were found to be in very good agreement with the experimental findings.