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University of Bath

Developing a film-riding pressure actuated leaf seal (FRPALS)

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

Test facility for characterising the performance of high-speed shaft seals
Test facility for characterising the performance of high-speed shaft seals

A challenge to seal designers

Shaft seals that reduce leakage are critical components in turbomachinery. Large rotating equipment often experiences rotor dynamic transients during start-up and shut down. These can lead to varying seal clearances. This is a problem for seal designers who need to minimise leakage and seal rubs that affect turbine performance.

The development of a film riding pressure actuated leaf seal (FRPALS) has shown encouraging signs at conceptual level to addressing these issues. The seal is able to maintain 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.

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 enough radial range of operation to follow the rotor during transients. It does this while mitigating the interference problems of friction, heat and wear.

Demonstrating the FRPALS concept

Our project aims to prove the FRPALS concept in a rotating environment and develop its technology readiness level. We have built a new experimental test rig to investigate the leakage mass flow-rate and seal displacements at engine realistic conditions.

We are carrying out this project in collaboration with Cross Manufacturing. They are a world-leading supplier of engine shaft seals to aerospace and industrial power industries. Cross have over 40 years' experience of designing, testing and manufacturing seal components.