Non-Linear Numerical Techniques for the Analysis of Turbomachinery Components

Reliability and structural integrity are two of the most important factors to be considered in rotating mechanical components design. Numerical techniques had shown to be necessary tools for the evaluation of mechanical components of power plants stations, and oil industry. According to the application, mechanical components are subjected to number of loads. As a consequence, relatively high stresses may occur on the component during service and its life time become limited. In this paper the non-linear numerical techniques more often used for that evaluation are presented. Two-dimensional non-linear boundary element and finite element methods are applied to obtain the stress measures for a turbomachinery component. Elastic analysis with large deformation is presented. The non-linear elastic boundary element implementation incorporates the displacement and the traction boundary integral equations as well as finite deformation stress measures. Boundary element programs, which are based on the non-linear theoretical approach has been developed. In order to evaluate the non-linear boundary element approach with domain type loading, a rotating disc case was analysed. This case study introduces a hyper-singular boundary element method which applies the sectorial symmetry concept that reduces the problem associated with the large number of boundary elements and internal cells in boundary element models of sectorially symmetric structures. Numerical results has been shown that the non-linear formulation lead to accurate solutions. Using an axisymmetric model of a low pressure steam turbine rotor of a 300 MW electric power unit a non-linear analysis was carried out. Results shown that the non-linear effect on the stress, strain and total deformation is located in the centre of the rotor near the surface of the central bore. From this, more mechanical damage can be generated after a number of cycles during the expected time life of the rotor.