| The aerostatic journal bearing is taken as the research object in this paper.A gas film model of orifice gas bearing is established.The variation of the flow field in the gas bearing is studied.The existence form of shock wave in the gas bearing and the effect of shock waves on the bearing characteristics are analyzed.And a method of controlling shock wave strength to improve bearing capacity is proposed.Firstly,the mathematical model of gas bearing is established by the finite difference method.The nonlinear dynamics theory is combined with the Reynolds equation to perform the coupling operation on the gas bearing flow field structure.The Newton iterative method is used to linearly process the Reynolds equation,and then the static and dynamic solutions of the gas bearing are obtained by numerical solution of the super-relaxation iterative method.Through the analysis of static and dynamic characteristics of aerostatic bearing,the variation law of bearing capacity with rotation speed is obtained.Then,it is difficult to clearly explain the problem of local flow field pressure dip in the numerical calculation method without considering the compressibility of the gas flow.Therefore,the three-dimensional model of aerostatic journal bearing is established considering the gas compressibility and viscosity,and the mesh is divided and the boundary of the model is determined.Using Fluent to simulate the flow field of the bearing film inside the bearing.The variation law of gas bearing capacity with steady speed and eccentricity in steady-state,and the change of gas pressure,velocity,density and Mach number with time near the orifice in transient-state are obtained.And the reason for the sudden drop of the flow field near the orifice is analyzed because of the shock wave caused by the annular region of the orifice.The shock wave intensity increases as the thickness of the gas film increases.The in-depth study on the formation process,the existence position and the influence of the shock wave on the flow field structure of the gas bearing are carried out.The research results show that the eccentricity of the bearing improves the load capacity by increasing the pressure difference inside the gas film.The load capacity also increases with the increasing supply pressure,but the increasing range gradually decreases or even decreases slowly with the increase of pressure.Because the Mach number near the orifice increases,the intensity of the shock in the flow field increases,causing turbulence of the local gas,causing a large amount of energy loss.The sufficient condition for the shock wave is that there is supersonic flow in the flow field,and the shock wave mainly appears in the gas bearing near the annular section of the orifice,so by changing the opening angle and angular depth of the gas bearing orifice is used to optimize the flow field structure in the gas mold to reduce the Mach number of local gas film,and the method of weakening the shock wave strength is obtained,thereby improving the bearing capacity of the gas bearing under high gas supply pressure. |
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