A Slow-Speed Rotating Test Facility for Characterising the Stiffness of Brush Seals

Abstract

An appreciation of the importance of bristle stiffening and hysteresis in brush seals has led to the development of a test facility capable of making stiffness measurements at different seal pressures. Engine scale seals are tested under engine representative differential pressures and eccentric movements in the test facility. To cover current and future sealing requirements the facility is capable of up to 12,5 bar differential pressures across the seal and eccentric rotor to casing movements of 2,5 mm. A slow-speed rotating rotor allows the dynamic friction directions of the contacting seal elements to be matched with the engine application. Both the eccentric cycle through which the seal is driven and the low-speed rotation of the central shaft are computer controlled to ensure known conditions are obtained and experimental repeatability. It has not been necessary to simulate engine temperatures, rotor speeds and radial growth between the engine and test facility. In this paper the test facility is fully described. Experimental results, showing torque, flow and stiffness characteristics from a typical prototype engine brush seal are reported, with full details of the experimental uncertainties. The effects of bristle stiffening, seal hysteresis, and bristle blow-down on the quantities above are detailed in the results.