This paper describes the pressure distribution in the bearing clearance of circular aerostatic thrust bearings with a single air supply inlet. For high air supply pressure, large bearing clearance and a relatively small bearing outer radius, it was believed that shock waves are caused and that a complex fluid flow structure is formed in the bearing clearance. Accordingly, analytical models based on the occurrence of shock wave in the bearing clearance have been proposed. Recently, very small aerostatic bearings have been used in various machine devices where the pressure distribution near the air inlets has a large influence on the bearing characteristics due to a short distance between air inlets and the bearing edge. In order to accurately predict various bearing characteristics for these kinds of bearings, a proper analytical model has to be established. However, it is very difficult to obtain the detailed information about the flow structure from flow visualization because of a very thin bearing clearance. Therefore, we calculated the flow field using computational fluid dynamics (CFD), which can solve the Navier-Stoke equations directly. It was found that the airflow just after entering the bearing clearance becomes turbulent in a region where relatively rapid pressure recovery occurs and that no shock wave is generated at the boundary between subsonic and supersonic flow. In addition, the numerical results presented show good agreement with experimental data.Copyright © 2006 by ASME

Numerical Calculations of Pressure Distribution in the Bearing Clearance of Circular Aerostatic Thrust Bearings With a Single Air Supply Inlet

In this report, the modified averaging approach to the solution for the dynamic performance of an externally pressurized, gas-lubricated, circular thrust bearing in a laminar flow regime, is presented under the assumption of a small harmonic vibration. This approach can evaluate the inertia effects under highly unsteady conditions. The accuracy of the approximate solutions presented in a previous report are compared and evaluated under similar conditions and the following conclusions are obtained: (1) The conventional averaging approach, in which all the inertia terms are averaged out across the film thickness, gives a good approximation. (2) The first-order solution of the perturbation method becomes remarkably inaccurate as the unsteadiness becomes high.

Effects of Gas Inertia Forces on Dynamic Characteristics of Externally Pressurized Gas-Lubricated Thrust Bearings : Evaluation of Various Approximate Solutions Under Highly Unsteady Conditions

In order to improve the pressure distribution, the aerostatic circular thrust bearing with single supply hole was studied. In the computational fluid dynamics (CFD) simulation, the laminar model, the turbulent model, the mixture model of laminar and turbulent were used simultaneously. The micro-characteristics of the gas flows were analysed based on the simulation results. One test rig was built for measuring the pressure distribution with the single test hole, and the calculated and experimental results were compared. The results showed that when the gas film clearance is small and the gas flow is subsonic completely, the whole gas flow is laminar flow, which should be calculated based on the laminar model and when the gas film thickness is large and there is supersonic flow in some region, which should be calculated according to the mixture model; at the same time, there is no surface of discontinuity for Mach number and pressure distribution, and no shock, and the pressure is recovered due to the boundary layer separation, the change of the flow state and the change of viscosity. The method for testing the pressure distributions with a single test hole is effective.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/joe.2018.8975

Research on flow characteristics of aerostatic circular thrust bearing

To improve the static characteristics of orifice-compensated aerostatic journal bearings (OCAJBs) under high gas supply pressures, governing equations considering inertial forces are established based on the shear stress transport (SST) k-ω turbulence model, and a double-row gas supply micron-groove orifice aerostatic journal bearing (MGOAJB) is designed. The influences of the structural parameters of the micron-groove orifice (MGO), such as the groove cross-sectional shape, dimensional parameters and layout, on the static characteristics under high gas supply pressures are studied. The SST k-ω turbulence model can accurately simulate the pressure distribution of a gas film flow field under high gas supply pressures, and the MGO can effectively improve static bearing characteristics such as the load capacity and stiffness. The influences of the groove cross-sectional shape, groove depth, and groove width of the MGO are not significant, but the groove length, orifice diameter, and MGO layout have obvious impacts on the load capacity and stiffness of a bearing. Structural parameters should be reasonably selected in the bearing design process.

Research on the effect of micron-groove orifices on the static characteristics of aerostatic journal bearings under high gas supply pressures based on the SST k-ω turbulence model


Purpose
The purpose of this paper is to derive the one-dimensional governing equations to describe the pressure distribution, load capacity and stiffness of aerostatic circular thrust bearing with a single air supply inlet.


Design/methodology/approach
The film flow field is divided into four regions: supply pressure region, pressure dropping region, pressure rising region and laminar flow region. The influences of bearing clearance and supply pressure on the pressure distribution, load capacity and stiffness of the bearing are presented.


Findings
With the large film clearance and large supply pressure, the oblique shock wave occurs near the entrance of gas film, which greatly increases the pressure drop region. Hence, it is not appropriate to consider the oblique shock as a normal shock.


Originality/value
This paper introduces the invariants at the entrance of gas film, employs the functional relationships between density and pressure, and provides the empirical formulas for the pressure dropping and rising regions. The pressure distribution curves are therefore illustrated through a considerably simplified computational process.


Study on the one-dimensional governing equations of aerostatic circular thrust bearing with a single air supply inlet

In this paper, two analytical models for an externally pressurized circular thrust bearing with a central supply hole are presented when the gas flow is choked at the inlet to the clearance space. These models can be modified for an unchoked condition and enable one to analyze the dynamic performance of the bearing over a wide range of design conditions. From the experiment, it is concluded that the effects of the inertia forces are considerable when the feeding parameter is small, and that the presented analyses yield good predictions of both the bearing stiffness and the damping coefficient.

Effects of Gas Inertia Forces on Dynamic Characteristics of Externally Pressurized Gas-Lubricated Thrust Bearings : Bearing Performance of Externally Pressurized Gas-Lubricated Circular Thrust Bearings with a Single Central Supply Hole in a Choked Condition

Fusao Mikami

Papers

Effects of Gas Inertia Forces on Dynamic Characteristics of Externally Pressurized Gas-Lubricated Thrust Bearings : Bearing Performance of Externally Pressurized Gas-Lubricated Circular Thrust Bearings with a Single Central Supply Hole in a Choked Condition

Effects of Gas Inertia Forces on Dynamic Characteristics of Externally Pressurized Gas-Lubricated Thrust Bearings : Evaluation of Various Approximate Solutions Under Highly Unsteady Conditions