Identification of stiffness and damping coefficients of hydrostatic bearing with angled injection

Abstract

This study deals with the experimental results obtained for a hydrostatic/hydrodynamic bearing used in aerospace turbopumps. This supporting element, if fitted with angled injection directed against shaft rotation, can provide a stabilizing effect to the rotor by reducing the circumferential flow. In order to characterize this effect and to improve its numerical simulation, an experimental housing has been designed to test the three directions of injection (radial, 25° and 50°). Measurements were obtained for the centered bearing operating at 2 kr/min, 4 kr/min and 6 kr/min with supply pressures of 2.5 MPa, 3.5 MPa and 4.5 MPa. The test rig uses hot water (<50 ℃) as a working fluid. For given operating conditions, a set of dynamic excitations imposed to the rotor provides complex impedances that are used for identifying dynamic coefficients. According to many pressure plugs distributed along the housing, the pattern of the pressure field in the recess and the thin fluid film near the recess is reconstructed. The bearing flow rate is also measured. Static and dynamic experimental results are compared with theoretical results obtained bycombining a pressure pattern model with a bulk-flow analysis. A good agreement between the two methods is observed. The measured cross-coupled stiffness is lower than the predicted one, indicating that the benefits of angled injection are better than what was predicted.