ANGLED INJECTION - HYDROSTATIC BEARINGS ANALYSIS AND COMPARISON TO TEST-RESULTS

Hydrostatic/hydrodynamic (hybrid) journal bearings handling process li quids have limited dynamic stability characteristics and their applica tion as support elements to high speed flexible rotating systems is se verely restricted. Measurements on water hybrid bearings with angled o rifice injection have demonstrated improved rotordynamic performance w ith virtual elimination of cross-coupled stiffness coefficients and nu ll or negative whirl frequency ratios. A bulk-pow model for prediction of the static performance and force coefficients of hybrid bearings w ith angled orifice injection is advanced. The analysis reveals that th e fluid momentum exchange at the orifice discharge produces a pressure rise in the hydrostatic recess which retards the shear pow induced by journal rotation, and thus, reduces cross-coupling forces. The predic tions from the model are compared with experimental measurements for a 45 deg angled orifice injection, 5 recess, water hydrostatic bearing operating at 10.2, 17.4, and 24.6 krpm and with supply pressures of 4, 5.5 and 7 MPa. The correlations include recess pressures, flow rates, and rotordynamic force coefficients at the journal centered position. An application example for a liquid oxygen hybrid bearing also demons trates the advantages of tangential orifice injection on the rotordyna mic coefficients and stability indicator for forward whirl motions, an d without performance degradation on direct stiffness and damping coef ficients.