Study Of Dynamic Characteristics And Steady State Performance On High-speed Micro Hydrodynamic Gas-lubricated Bearing

With the rapid development of micro-electrical mechanical systems(MEMS),the bearings,as a support component of small scale and high rotation speed revolving equipments,are improved continuously.Gas bearings have some outstanding advantages,such as compactness,stable operation at the lower or higher temperature,etc.The stable,effective and safe operation of MEMSs is mainly determined by the bearing performance.In this thesis,the hydrodynamic characteristics of the micro gas bearing are investigated by numerical simulation method.The results will provide the valuable guide to the reasonable design and the stable operation.Firstly,the hydrodynamic characteristics of the gas film inside a wedge-shaped micro channel are analyzed by combined the Navier-Stokes equation with the modified Maxwell boundary slip.It is found that the change in the load capacity is related to the fluid backflow in the cases of different factors.When the tilt angle of the tilt plate increased,the load capacity decreases due to the appearance of the backflow in the channel.However,increasing the channel height leads to the decrease in the load capacity,which is not impacted by the backflow.In addition,raising the temperature of the gas film results in the stronger boundary slip and the weaker backflow.The larger gas viscosity make the backflow emerge at a greater tilt angle.Furthermore,the static characteristics of the grid gas journal bearing are studied by using a modified Reynolds equation based on the thin film flow.It is found that when the eccentricity ratio and the rotation speed are increased,both the load capacity and stability enhance.In particular,the enhancement is much shaper at a large eccentricity ratio and a lower rotation speed.Additionally,the longer bearing would effectively improve the bearing performance.Finally,the relationship between deformation and pressure for the foil bearing and the thrust bearing are examined by coupling the structure with the fluid flow.The difference from the grid journal bearing,the pressure distribution along the circumferential direction for a foil bearing is zigzag,and thus decreasing the pressure.Moreover,it is found that the deformation degree of the top foil and the bump have significant influence on the bearing load capacity.For the thrust bearing,the high pressure region on the tilt pad is concentrated on the region near the thinnest film.The high pressure region gradually shifts to the edge and center with the tilt angle and the film gas increasing,respectively.