NUMERICAL ANALYSIS OF THE MODAL PROPERTIES OF A SHROUDED TURBINE BLADING

Abstract eng:
Presented work is concerned with the numerical analysis of natural frequencies and corresponding mode shapes of twisted blades with contacts between blade shrouds. The blades are modelled by means of the Finite Element Method (FEM) using Rayleigh beam elements with varying cross-sectional parameters along the elements and six degrees of freedom (DOFs) in each of nodes, while the rhomboidshaped shrouds are considered to be rigid. The blades are clamped into a rotating rigid disk. Since the finite element models based on the Rayleigh beam theory tend to slightly overrate natural frequencies and underrate deflections in comparison with finite element models including shear deformation effects, parameter tuning of the blades is performed. The modelling of interactions at the contact surfaces of neighbouring blade shrouds is carried out using a multipoint frictionless contact approach with constant normal contact stiffness. In order to compare the natural frequencies, three different geometries of the blade shroud as well as three different values of the pre-twist angle induced by preloads at the contact interfaces are tested.

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