Numerical analysis of dynamics and durability of rotor elements in gas turbine engines

Abstract

In this work, an accurate algorithm for calculating the durability of rotor wheels in gas turbine engines undergoing detuning of parameters was developed. The finite element method, underlying the Ansys Software, was used for modelling free and forced oscillations of rotor wheels. During the experiments, the detuning was simulated by attaching additional masses to the wheel blades. The calculations of frequencies, modes of forced oscillations, as well as dynamic stresses arising due to these oscillations, were carried out using the Fourier series. The schematisation of dynamic stresses, i.e. differentiation of obtained stresses into levels having specific amplitudes, was used to calculate durability. The main research result comprises the developed algorithm for calculating the durability of rotor wheels of gas-turbine engines subjected to parameter detuning. This algorithm served as a basis for the Ocs_Rotor software for investigating the natural oscillations of blades and rotor wheels under parameter detuning. Using this software, the natural frequencies and oscillation modes of the blades were calculated. Dynamic stresses under forced oscillations, as well as durability of the rotor wheel, were calculated using the obtained results. The results of calculating the service life of an actual rotor wheel having three different positions of blades under detuning allowed the construction having the maximum service life of 1.75 * 105 hours to be selected. Comparing the results of calculations, obtained using the Ocs_Rotor software, with those of field experiments, carried out at Brandenburg Technical University (Cottbus, Germany), demonstrated high accuracy characterised by a maximum error of 4 %. This suggests that the software may be used to design structures of maximum service life. The results of durability calculations of an actual rotor wheel having different blade positions under detuning allowed practical recommendations for engineers on the positioning of the blades in the wheel to be established.