Reduced-order modeling of turbine bladed discs by 1D elements

Abstract

The dynamic behavior of turbine bladed discs is deeply influenced by blades geometry, which is determined as a compromise between fluid-dynamic and mechanical needs. One of the most important issue from the mechanical side is the tailoring of the dynamic characteristics to allow a sufficient separation between the natural frequencies and the harmonics of the rotational speed. The most common approach to predict the natural frequencies of bladed discs involves the realization of 3D FE models using solid elements. This approach is highly demanding in terms of time for the realization of the models as well as for the computation, even when only one blade if explicitly modeled and a cyclic symmetry constraint is employed. In this work, we propose a reduced order model based on mono-dimensional finite elements. The proposed element is based on the Timoshenko beam formulated for non-symmetrical cross sections. The shape functions are based on the exact solution of the beam equation to avoid shear-locking. Torsional stiffness includes the effect of warping. The proposed model is compared with accurate 3D FE models in terms of modal properties. Blades of different shape and slenderness taken from turbine and compressor of a large gas turbine are considered.