The Aerostatic Seal: Analysis and Development of a New Dynamic Seal Concept for Steam Turbine Application

Abstract

This thesis describes the development of a new seal concept for steam turbines called the Aerostatic Seal. The Aerostatic Seal is a dynamic seal, and so can respond to rotor radial movement to maintain a low clearance between the seal and the rotor. As the seal is dynamic, smaller clearances can be achieved without rotor contact compared to conventional static seals such as the labyrinth seal, hence increasing the efficiency of the turbine through reduced leakage. Furthermore, as the seal is dynamic it can tolerate larger radial transients typically found during start up and shut down of the steam turbine, and so also contributes to increasing the flexibility of the turbine plant.

In this thesis an analytical design and analysis methodology was developed for the Aerostatic Seal. The methodology was used to generate a number of seal designs which were experimentally tested in a non-rotating test facility using room temperature air. The results confirmed that the seal would operate dynamically, and the experimental campaign provided valuable data on the operation of the seal. The non-rotating rig was also used to test a second generation seal design.

The seal was then tested in a rotating test facility, which modelled high speed rotor radial transients with an adjustable eccentric rotor. The Aerostatic Seal demonstrated the ability to respond to high speed transients.

A final test campaign was conducted in the high temperature steam rig at TU Braunschweig, Germany, enabling experimental demonstration of the Aerostatic Seal using realistic materials and represented realistic steam turbine conditions.

Finally, based on the experimental and analytical work carried out within this thesis, a proposed Aerostatic Seal design for steam turbine implementation is presented.