Film Riding Leaf Seals for Improved Shaft Sealing

Abstract

Turbine shaft seals are vulnerable to rubs caused by thermal distortion, mis-alignment and rotor dynamic vibration that are often not well understood. When seals rub as a machine is brought up to operating conditions performance is compromised due to increased seal leakage. Much effort has been extended in recent years to develop seals that mitigate those losses. This paper presents a seal design with segmented film riding runners capable of non-contacting seal operation during rotor transients. Operating differential seal pressure displaces seal leaves and attached runners toward the rotor surface until balanced by hydrostatic and hydrodynamic lift. Sufficient radial range of operation is provided to follow the rotor seal surface during transients while maintaining a small seal clearance. Seal design features and function will be described and illustrated along with analysis of forces and motions for a sample application. Planned modeling and testing will also be presented. This concept promises enhanced shaft sealing by combining a leaf seal structure that provides a large range of motion to avoid rubs during startup and shutdown with runner elements capable of generating hydrostatic and hydrodynamic lift forces to maintain shaft–seal separation during all rotor displacement transients. Improved turbine performance from small operating seal clearance and extended seal life without rubs are expected benefits of the Film Riding Pressure Actuated Leaf Seal (FRPALS).