Measurements Versus Predictions for the Dynamic Impedance of Annular Gas Seals—Part I: Test Facility and Apparatus

Abstract

An experimental facility and apparatus are described for measuring the dynamic impedance and leakage characteristics of annular gas seals. The apparatus currently has a top speed of 29,800 rpm and can accommodate seal diameters up to 114.3 mm. The air-supply system can provide up to 13.79 MPa (2000 psi) of pressure at the seal inlet. Test seals are configured in a back-to-back arrangement inside the stator and air enters a central inlet annulus at two opposed radial positions. Labyrinth seals and bleed ports located outboard of each test seal are used to control the pressure drop across the test seals. Two orthogonal, external hydraulic shakers are used to excite the test stator at frequencies up to 400 Hz. At a given operating condition, the apparatus can measure the rotordynamic impedance of a pair of identical seals over a broad frequency range using a single pseudo-random excitation waveform. Measurements are also made of seal leakage rates and upstream and downstream temperatures and pressures.