Reduction of Pressure Forces in Turbine Labyrinth Seals

Abstract

The paper describes a chamber seal reducing the aerodynamic forces created in shroud seals. This kind of turbine seal was patented and tested. The investigations into the pressure field in the shroud gap were performed by means of CFD Fluent Code and compared with the results measured on a single-stage air model turbine of the impulse type. Special attention was paid to the pressure field in the rotor blade shroud clearance in the situation when rotor-stator eccentricity led to asymmetrical flows in blade passages and shroud gaps. The investigations were carried out for different types of shrouds, various shapes and dimensions of the chambers, and for different turbine working conditions. The calculations were verified by the experimental research. The performed investigations proved that the chamber seal could remarkably reduce aerodynamic forces generated in turbine clearances due to rotor-stator eccentricity. The results proved that: - the proposed chamber seal can reduce pressure forces acting on the blade shroud by about 30%–60%, depending on the type of the shroud; - the chamber seals are specially effective in the case of relatively small radial clearances; - the proposed method may be applied in active control of aerodynamic forces generated in turbine shroud seals; - the presented seal modification can be easily introduced to turbines in operation and to the newly-designed ones. It must be emphasized that according to the calculations and experiments the application of the chamber to typical labyrinth shroud seals does not affect the flows in the turbine blade channels.