A Test Facility for the Measurement of Torques at the Shaft to Seal Interface in Brush Seals

Abstract

An important factor in the performance of brush seals for a wide range of gas turbine applications is the rate of wear at the seal to shaft interface, which is dependent on the contact pressure that exists between the bristles and rubbing surface. This is dependent on a variety of effects. Principally, these are the aerodynamic forces bending the bristles onto the rubbing surface, frictional effects within the bristle pack and at the backing ring that arise with the application of pressure differential, geometrical changes due to centrifugal and thermal growths, and transient differential movements of the rotor that develop in flight manoeuvres. In order to investigate the effect of these phenomena on contact pressure, a test facility has been devised in which the torque exerted by a brush seal on a rotating shaft is used as an indirect measurement of contact pressure. This has necessitated the design of a test facility in which all system torques can be fully calibrated. Consequently, a pressure balanced design has been adopted in which applied seal differential and pressure levels have a minimal effect on axial loads at the rotor bearing assembly. The primary method of torque measurement is the instantaneous deceleration of the rotor. Thus, measurements over a wide speed range are acquired with high frequency instrumentation. The means whereby small parasitic torques are evaluated and corrected is given. Results demonstrating the dependence of contact pressure on seal differential and pressure levels are presented.