Unsteady Rotor Blade Forces of 3D Transonic Flow Through Steam Turbine Last Stage and Exhaust Hood with Vibrating Blades

Abstract

Presented below are numerical calculations of the 3D transonic flow of an ideal gas through a steam turbine last stage with the exhaust hood, taking into account blade oscillations. The approach is based on a solution of the coupled aerodynamic-structure problem for 3D flow through a turbine stage in which fluid and dynamic equations are integrated simultaneously. This provides the correct formulation of the coupled problem because the blade oscillations and loads are a part of solution. An ideal gas flow through stator, rotor blades and the exhaust hood is described by unsteady Euler conservation equations, which are integrated using the explicit monotonous finite-volume difference scheme of Godunov-Kolgan and a moving hybrid H-H grid. The structure analysis uses the modal approach and 3D finite element model of a rotor blade. The pressure distribution behind the rotor blades were non-uniform on account of the exhaust hood. In the nominal condition a self-excited rotor blade vibration was discovered.