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

Abstract

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 predict various bearing characteristics accurately 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, which can solve the Navier-Stokes 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.

CFD Investigation of an Aerostatic Thrust Bearing Flow Field with New Type of Throttling Structure

“…In this paper, the conservation form of the Navier-Stokes equations for steady, compressible flow is being solved for the turbulent flow cases. The indicial notation form of these equations in the Cartesian coordinates is written as [3]:…”

“…A significant amount of work, both theoretical and experimental, has been published over the years on the various parameters affecting the performance of these bearings, for example, Sadek.Z [1] carried out an experiment investigation of an aerostatic bearing, the results shows that as the supply pressure and film thickness increases the dimenslonless load carrying capacity decreases and the lubricant mass flow rate increases. Renn [2] carried out the experimental and CFD study on the mass flow-rate characteristic through an orifice-type restrictor in aerostatic bearings, the results shows that the mass flow-rate characteristic through an orifice is different from that through a nozzle.Yoshimoto [3] used CFD method studied the pressure field and shock wave distribution, their results reasoned pressure depression to the transition from laminar to turbulent flow and claimed that no shock wave is generated at the boundary between supersonic and subsonic flows. Eleshaky [4] studied two typical air thrust bearing using CFD method, the results showed that the predicted pressure distributions along the fluid film compare well with the corresponding experimental data of other investigators, and the work allowed a clear capturing of the coherent structures of the flow field in the bearing inlet region which include the coalescing of compression waves into shock waves and the region of shock boundary layer interaction (pseudo-shock).…”

Research and Analysis of the Static Characteristics of Aerostatic Bearings with a Multihole Integrated Restrictor

“…When gas flows from the outlet and produces a pressure drop, the aerostatic film has a certain bearing capacity and stiffness. Due to their high accuracy of motion, wide speed range, small amount of friction, lack of pollution, and low heat generation, aerostatic bearings have been widely used in the aerospace industry and the IT chip manufacturing industry, as well as for the manufacturing of ultraprecision equipment and national defense application equipment in addition to other fields and applications [1][2][3]. With the development of precision and ultraprecision technology, higher and more urgent requirements have been proposed for the stiffness, accuracy, and stability of aerostatic bearings [4][5][6].…”

Numerical Simulation and Experimental Verification of the Stiffness and Stability of Thrust Pad Aerostatic Bearings

“…Chen et al [18,19] demonstrated that micro-vibration was closely related to air vortices that appeared near the air inlet of the aerostatic bearings and that the strength of these air vortices could be represented by a pressure drop from the edge of the vortex to its center. Mohamed and Yoshimoto indicated that a shockwave occurred during the transition from subsonic to supersonic and that the airflow transition between laminar and turbulent flow led to a pressure drop and recovery in the bearing clearance [20,21]. To date, there is no suitable method to address the contradictory relationship between stiffness and vibration in aerostatic bearings with orifice restrictors.…”