Theoretic And Experimental Analysis On Bearing Performance Of Porous Aerostatic Bearing

With the increase of requirements to practical engineering of high performance and high precision and no friction bearing,aerostatic bearings are used more and more widely in the fields of aerospace,precision machinery,precision instrument,precision machinery.Due to the pore characteristics of its own structure,porous materials provide tens of thousands of micro orifice,the effect of gas in the porous material through the densely covered orifice is better than that in general,make the bearing capacity and stiffness better.And as a result of the gas film gap is one side of the permeability of the material,when the rotor rotation,the porous material inside the gas will flow,so that the bearing has a better damping characteristics.The gas motion model in porous material is established by using Darcy's law.The Reynolds equation of gas flow in the gas film region is established based on the gas equation of motion,continuity equation and gas state equation,and modified by the velocity slip theory.Coupling the pressure distribution equations in the porous region and that in the gas film region.Reasonable boundary conditions are established in the solution domain of the gas membrane,using the Galerkin method and according to the conditions of weak solutions to get the functional film of air pressure distribution.The discretization is carried out by the finite element method and using the interpolation function for calculation to obtain the programmable form of the pressure distribution equation.Through MATLAB programming,the pressure distribution of each node in the film by Over-relaxation iterative method.The bearing capacity,static stiffness and gas flow rate were further obtained.And he effects of velocity slip coefficient,porous material permeability and gas pressure on the static characteristics are analyzed.Based on the solution of the steady-state Reynolds equation,the bearing rotor system is transformed into the stiffness-damping system by using the small perturbation method.Introduce small perturbations in the direction of the eccentric angle and eccentricity.The gas film thickness and pressure terms are expanded by using Taylor's formula,and the perturbed equations in the porous region and the gas film region are obtained.Based on the simultaneous solution of the perturbation equations in the two region,the dynamic Reynolds equation of the gas film is obtained.The discrete solution of dynamic Reynolds equation by finite difference method,the use of MATLAB programming through the dynamic pressure over relaxation of each node in the distribution of gas film.Then the dynamic characteristic coefficients of the bearing are obtained,and the influence of the parameters on the dynamic characteristics of the bearing is analyzed,such as the permeability of porous materials,the thickness of the gas film and the disturbance frequency.On the basis of theoretical analysis,the experimental platform of static characteristics of the porous static gas thrust bearing is set up.The permeability of porous materials were measured and calculated by experiments,The bearing performance test of a porous aerostatic thrust bearing is carried out,and the influence of the bearing parameters on the static characteristics is analyzed,and the correctness of the theoretical analysis is verified.