The Influence of Erosion Wear on the Gas Dynamic Indicators, Strength, and Dynamic Characteristics of the T-35/59-1.3 Steam Turbine Last Stage Rotor Blades

Abstract

Erosion wear of the blade airfoil causes essentially worsened conditions of its streamlining and, hence, a decrease in the steam turbine unit stage efficiency as a whole, as well as the occurrence of vortex zones, which in turn may cause some loss of the blade row aeroelasticity. The article addresses a study of the effect of progressive erosion wear on the turbine stage economic efficiency and strength reliability, and a method for predicting the change in its characteristics throughout the service life is proposed. A classification of erosion kinds in steam turbines is given. Criteria, basic methods for decreasing the influence of erosion wear, and the droplet erosion mechanism are considered. Generalized results of experiments on studying the erosion wear of the last stage blades in OK-12A turbine drives and PT-25-90/10 steam turbines are given. The article also presents an assessment of how this wear affects the turbine machine stage gas dynamic parameters based on the results of CFD simulation of the flow in the blade after it has been in operation from 10 to 120 thousand h, and also the rotor blade strength and dynamic characteristics. The article gives the results of calculations showing essential decrease in the stage efficiency with respect to its nominal value for the ideal blade profile, static strength calculations, and modal analysis of the blade that had experienced wear for 120 thousand h of operation, which were carried out using the finite element method (FEM) on a 3D model. In solving the elasticity theory FEM problem, the blade stress-and-strain states before and after it had been in operation for 120 thousand h were determined. In the course of a computational study carried out using the ANSYS Mechanical software system, data have been obtained testifying that the blade erosion wear occurred for 120 thousand h of blade operation does not degrade its static strength and standardized detuning from resonance for the operating rotation frequency.