Design of Floated Shoe Close Clearance Seals for Supersonic Jet Engine Compressors

Abstract

The increase in engine efficiency to be gained by substituting a floated close running air seal at the high pressure end of large jet engine compressors, in place of the labyrinth seal, has prompted an intensive effort to design such seals for experimental evaluation. This paper describes the design of both a radial and an axial version in which multiple segmental shoes are floated 0.001 in. from the high speed runner surface. In the radial version, the shoes are free to float radially in order to follow runner runout. In the axial version, the shoes track the runner runout by floating axially in a carrier which moves to accommodate 0.4 inch of differential expansion. Floating is achieved through hydrostatic action sustained by the pressure difference across the seal. A shrouded Rayleigh step profile on the primary (high speed rubbing) seal surface provides additional protection. An order of magnitude reduction in leakage rate is predicted.