Design Optimization and Analysis of a Steam Turbine Rotor Grooves

Abstract

A large variety of turbo-machinery rotor groove geometries are used in industry. However, there is no specific attempt made to compare them on the basis of performance. This paper provides an attempt to fill that gap aiming to find an optimum geometry. The main objective of the investigations is to reduce fillet stress concentration factor and associated deformations. The present work carries out the design modification of fillet of a Steam Turbine Rotor. Finite Element Analysis is performed using ANSYS Workbench that is used to determine the fillet stresses effectively to modify the blade rotor grooves. The low pressure steam turbine rotor blades have usually a history of stress failure. They suffer from tensile and bending stresses partly due to the centrifugal force as a result of high rotational speeds and partly due to high pressure, temperature and speed steam loading. The centrifugal force is one of the problems that face the designers of turbine blades especially the long ones. The designer always aims at reducing these stresses. One way to do so is by the reduction of stress concentration factor which takes place between the rotor and its groove. That is to make the rotor blade of variable cross section instead of straight. This paper presents the method of reducing stress concentration factor as well as reduction in the deformation of the rotor.