Rotor Design in Industrial Gas Turbines

Abstract

The various design aspects of an industrial gas turbine rotor need special attention to ensure safe and reliable operation of the entire machine. The rotor has to fulfill the following main criteria and tasks: carry the blading, transmit the torque, define the aerodynamic channel geometry, guide the cooling air, provide sealing and bearing surfaces, and exhibit acceptable rotordynamic behavior. Additional criteria linked to the rotor design can be established, i.e., ease of manufacture and assembly, maintainability (where needed), transient blading tip clearances, rotational inertia, balance of axial thrust, and safety against fault conditions (blade loss, short circuit, hot-gas ingestion, etc.) with possibilities for subsequent repair. Industrial practice shows that there are several design approaches possible. This paper describes the general requirements and how to assess the strength and the dynamic behavior under transient and steady state conditions. Additionally, the individual existing main design principles, i.e., stacked discs with individual centering and tie rod types, and monolithic or welded integral rotor design, are compared. Differences in levels of loading and in the dynamic behavior are outlined. Finally, an assessment of the individual rotor designs under fault conditions is given, and critical areas of the component under such conditions are discussed.