3D Finite Element Structural Analysis of Attachments of Steam Turbine Last Stage Blades

The work presents the results of finite element (FE) simulation and study of 3-D stress-strain state of attachments of steam turbine last stages blades performed with the use of the ANSYS FE software. The attachments of the steam turbine last stages blades consist of a great deal of structural elements (e.g. rivets, forks) that have complicated geometrical shape and are in contact interaction with each other. To obtain the FE results, correctly describing local stresses and to reduce the computation time, a series of 3-D finite element models has been built and a method of multi-level submodeling has been used. In the process of the finite element study of the 3-D stress-strain state of the blades attachments the following models have been used: 1. Initial model – a macro-model incorporating a disc sector and a blade with a shroud flange, damper links, and the attachment; 2. First-level submodel comprising a blade attachment and a disc sector; 3. Second-level submodel intended for correct determination of local stress fields in rivets. With the use of the method of multi-level submodeling on a submodel 717675 degrees of freedom, fields of local stresses and strains for the rivets have been obtained. To calculate the complete model without applying the method of multi-level submodeling, it would be necessary to solve a problem of 3-D contact interaction with as many degrees of freedom as 1102743. As a result of the finite element simulation performed with due regard to the 3-D multiple contact interaction of the blade tail and the disc, there have been revealed the areas where the equivalent, Mises stresses exceeded the yield strength. The practical recommendations have been worked out allowing reduction of the equivalent stresses in the mentioned areas.
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