Study And Application Of Convective Heat Transfer In Boundary Layer Of High Pressure Circular Gas Bearing

In the gas film of high pressure circular gas bearing,airflow is accelerated to supersonic speed,temperature gradient of airflow is large and convection heat transfer between airflow and bearing wall is obvious,so the impact of thermal load on the deformation of bearing disk cannot be ignored.Therefore,the study of convection heat transfer characteristics of boundary layer is the basis for further study of bearing thermal deformation and design of bearing structure.The flow field in the gas film of bearing is solved numerically,and then the influences of gas film clearance,gas inlet pressure and bearing radius on the boundary layer of gas film are analyzed.The results show that decreasing gas film clearance and gas inlet pressure,as well as increasing bearing radius,can promote the development of gas film boundary layer;the mainstream is submerged by the boundary layer which has been fully developed,and the viscous force in the boundary layer acts on the airflow,causing the decline in airflow velocity and keeping the pressure in the gas film at a high level,thereby the load carrying capacity of the gas bearing is improved.According to the numerical calculation results,the working parameters of experimental mode of high pressure circular gas bearing are determined.The convective heat transfer coefficient between gas bearing wall and airflow is calculated.The reliability of numerical results is validated by comparing the results with the bartz formula.The influences of total gas inlet pressure and temperature on the convective heat transfer coefficient were analyzed.The results show that the convective heat transfer coefficient increases when the total gas inlet pressure increases,and it declines when the total gas inlet temperature increases.The distribution characteristics of convective heat transfer coefficient were analyzed.The results show that with the increase of bearing radius,Reynolds number declines,so the convective heat transfer coefficient tends to decline;the airflow velocity declines from supersonic to subsonic speed,causing the rapid decline of convective heat transfer coefficient;the boundary layer of gas film converges,causing the increase of convection heat transfer coefficient.The deformation of bearing under the combined action of pressure load and thermal load is calculated by the finite element analysis method.The results show that the deformation of carbon steel bearing caused by pressure load is only 20.2% of the thermal deformation.The influences of material quality,bearing disc thickness and different bearing structure on the deformation of bearing disc were analyzed.The results show that the thermal deformation of carbon steel bearing disk increases with the increase of bearing disc thickness,while the deformation of transparent quartz glass bearing disk declines,then the suitable design structure of experimental model of high pressure circular gas bearing with different materials is determined.