Analysis on Static Characteristics of a Hybrid Gas Thrust Bearing with Full Porous Compensation and Spiral Grooves Considering Slip and Tilt Effects

An innovative hybrid gas thrust bearing with full porous compensation and spiral grooves is proposed to improve the static characteristics of the bearing especially operating at high speeds. Considering the effects of velocity slip and bearing tilt, a static model is developed by using the finite volume method and boundary-fitted curvilinear coordinate system for the proposed bearing. The three-dimensional feed flow equation and the nonlinear discretized modified Reynolds equation are solved by the successive over-relaxation and Newton-Raphson schemes, respectively. The static model is validated by comparing with the available theoretical and experimental data for the conventional hydrostatic porous and hydrodynamic spiral-groove gas thrust bearings. The effects of groove, slip and tilt on the static characteristics of the hybrid bearing are investigated under different operating conditions. The calculated result shows that, the hybrid bearing can be superior to the conventional purely hydrostatic type in all static characteristics especially at high compressibility number Λ and low feeding parameter ΛΦ and supply pressure; the load capacity and static stiffness of the former can be up to 11.5 times and 7.4 times, respectively, as much as these of the latter, and the mass flow rate of the former can be only 1/10 of that of the latter. The slip effect on the load capacity and mass flow rate increases with Λ as well as ΛΦ, leading to deviations of less than 9% and 32.1%, respectively; the slip effect is to reduce the static stiffness at relatively low ΛΦ but to increase the static stiffness slightly at higher ΛΦ, resulting in deviations of less than 8.2%. With the increase of tilt ratio, the load capacity and moments increase, but the static stiffness and mass flow rate decrease. As the eccentricity ratio increases, the load capacity increases and the mass flow rate decreases especially at high compressibility numbers; while the variation of the static stiffness is still related to the compressibility number.