13 - Development of last-stage long blades for steam turbines

Abstract

The aim of this chapter is to present development and design technologies and methodologies of last-stage long blades for large-scale steam turbines for modern power plants. Technical features of last-stage long blades are high centrifugal force, high blade speed, three-dimensional flow, wet steam flow, and relatively large unsteady flow forces during low-load operations. These features are the result of the required large annulus areas that are required, which make last-stage long blade developments difficult. Furthermore, as the name suggests, last stages with exhaust diffusers need to be designed carefully to minimize the leaving loss because there is no stage that uses the exit steam. Therefore, new technologies for aerodynamic design, mechanical and aeromechanical design, and material design are required when we begin new longer-blade development. In this chapter we present modern technologies and methodologies with some case examples.