Inherent restriction on stability of rotor‐aerostatic bearing system

Abstract

Purpose -The purpose of this paper is to study the influences of both the number and locations of entry holes on the static and dynamic characteristics of a rigid rotor supported by two double-rows, inherently compensated aerostatic bearings. Design/methodology/approach -The air is assumed to be perfect gas undergoing the adiabatic process and passing through entry holes into the bearing clearance. Air film in the clearance is governed by Reynolds equation including the coupled effects of wedge due to rotor rotation and squeezed film due to rotor oscillation. Findings -The method is used to analyze Reynolds equation, which is then solved by the finite difference method and numerical integration to yield static and dynamic characteristics of air film. The equation of motion of the rotor-bearing system is obtained by using the perturbation method and the eigensolution method is used to determine the stability threshold and critical whirl ratio. Originality/value -The paper considers the eccentricity, rotor speed, and restriction parameter in the analysis of the whirl instability of the rotor-aerostatic bearing system for the comparisons between various designs in the number and locations of entry holes of aerostatic bearings.

Investigation on backflow phenomenon in the aerostatic journal bearing

“…where i and j represent the relative position of the discretized grid point in the gas film, k is the kth term of the transformed pressure P i,j which is calculated for each time iteration using equation (13).…”

“…The finite volume method (FVM) 14–21 and finite difference method (FDM) 13,22–29 are widely employed as the numerical methods for solving the partial differential equations in aerostatic bearing publications. The FVM has many advantages compared with FDM for either two-dimensional or three-dimensional fluid flow.…”

“…Although FVM is more suitable for bearing problems in general, the FDM is usually applied for the discretization of the Reynolds equation, as found in the literature, when the mesh is two-dimensional and structured. 13,23–30 FDM is employed to discretize the partial differential terms of the Reynolds equation in this work.…”

“…Chen et al investigated numerically the stability performance of rotor-aerostatic journal bearing. 13 It was found that journal bearings with feedholes located towards the lower end of the piston during high speed operation were more prone to the backflow phenomena because the hydrodynamic pressure was mainly confined in this location which was larger than the supply pressure at that feedhole.…”

Multi-Physics Fields Based Nonlinear Dynamic Behavior Analysis of Air Bearing Motorized Spindle

“…Other method such as rational function approximation to the resulting impedances [14] and recursive least square method [15] are also used to obtain the dynamic coefficients of air bearing. When investigating the nonlinear dynamic behavior of the ABMS by applying the dynamic coefficients method, the dynamic coefficients are usually regarded as constant which improves the efficiency indeed, but ignore the influence caused by the variation of the dynamic coefficients [16][17][18]. The dynamic coefficients method is based on the acquisition of dynamic coefficients while the restoring force method can be obtained directly by solving the transient Reynolds equation.…”