A test facility for the measurement of torques at the shaft to seal interface in brush seals

An important factor in the performance of brush seals for a wide range of g as turbine applications is the rate of wear at the seal to shaft interface, which is dependant on the contact pressure that Exists between the bristle s and rubbing surface, This is dependent on a variety of effects, Principal ly: 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 chan ges due to centrifugal and thermal growths, and transient differential move ments of the rotor that develop, in flight manoeuvres. In order to investig ate 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 shaf t is used as an indirect measurement of contact pressure. This has necessit ated the design of a test facility in which all system torques can be fully calibrated Consequently a pressure balanced design has been adopted in whi ch applied seal differential and pressure levels have a minimal effect on a xial loads at the rotor bearing assembly. The primary method of torque meas urement is the instantaneous deceleration of the rotor. Thus, measurements over a wide speed range are acquired with high frequency instrumentation. T he means whereby small parasitic torques are evaluated and corrected is giv en. Results demonstrating the dependence of contact pressure on seal differ ential and pressure levels are presented.