Department of Mechanical Engineering

Development of a film riding pressure actuated leaf seal (FRPALS)

We are developing a novel type of shaft seal to reduce leakage losses in high pressure gas turbines.

A challenge to seal designers

Seals between high and low pressure turbine sections that reduce leakage are critical components in turbomachinery. During start-up and shut-down, the rotor dynamic transients often experienced in large rotating equipment can lead to varying seal clearances. This poses a challenge to seal designers, whose goal is to minimise leakage and seal rubs that can be detrimental to the turbine performance.

The development of a Film Riding Pressure Actuated Leaf Seal has shown encouraging signs at conceptual level to address many of these issues. The seal is capable of maintaining a small, non-contacting clearance under all transient and operating conditions.

The patented design incorporates two sets of axially displaced seal leaves with attached segmented runners. The presence of a differential pressure acting across the seal encourages the leaves and runners to displace in the radial direction until balanced by hydrostatic and hydrodynamic lift at a small clearance. The seal design provides a sufficient radial range of operation to follow the rotor during transients whilst mitigating against the interference problems of friction, heat and wear.

A cut-away view of the Film Riding Pressure Activated Leaf Seal (FRPALS) concept showing the internal features of the sealDemonstrating the FRPALS concept

The aim of our project is to demonstrate the FRPALS concept in a rotating environment and develop its technology readiness level. A new experimental test rig at the University of Bath is currently being designed and manufactured as part of this proposal. The rig will have the capability to measure mass flow leakage and seal displacements at engine realistic conditions.

Our project is conducted in collaboration with Cross Manufacturing, a world leading supplier of engine shaft seals to the aerospace and industrial power industries. Cross have over 40 years’ experience of designing, testing and manufacturing seal components.