Analysis Of Hybrid Bearing’s Dynamic Characteristics And Oil Film Stablity

Hybrid bearing is widely used in the field of high-speed grinding machinebecause of its high accuracy, high dynamic stiffness, high damping performance andlong life. However, with further increase of spindle speed, high-speed spindle systeminstability occurs due to scraping, axle and other phenomena, thus result in systemfailure. Meanwhile, when the system working in the condition of high speed, a kind ofunique hybrid bearing failure-the film oscillation problems occurs, which easily leadto oil film instability. The key of high speed spindle system vibration and stabilityanalysis lies in the calculation of dynamic characteristics of hybrid bearing. Thispaper summarizes a large number of previous study on dynamic characteristics and oilfilm stability analysis of hybrid bearing. On the basis of such study, this paperproposed a new approach to analysis hybrid bearing’s dynamic characteristics and oilfilm stablity, which based on CFD. This work consists of the following elements:Firstly, the CFD model of hybrid bearing is built, and then the calculationconditions for solving the model is determined. The finite volume control equationsbased on dynamic mesh method for solving usteady flow field, which caused by thedomain changes, is built. The self-developed dynamic mesh update method, whichembedded UDF, is proposed to avoid mesh distortion caused by movem ent of thejournal.Comparing with oil force under the condition of transient state, the distinctionof displacement perturbation and velocity perturbation is defined.Secondly, the stiffness and damping coefficients of hybrid bearing are calculatedby applying the approach combined with the perturbation theory. A custom program isbuilt to define the motion parameters. The film grid is updated based on dynamicmesh model. By solving the N-S equation, the changing oil force is cacluated duringthe journal movemengt, thus the stiffness and damping coefficients is calculated byusing finite difference method. At last, the effects of rotation speed and oil pressureon hybrid bearing dynamic coefficients is analyzed.Finaly, aiming at overcoming the deficiency of available methods for revalingthe nonlinear dynamic behaviors of complex rotor-bearing system, a fluid-structuremethod which combined rotor dynamics with computational fluid dynamics based ondynamic mesh is proposed. This method presented in this paper first developed arotor-bearing system, then calculated the transient oil field of journal bearing by usinga dynamic mesh method for variable flow, thus calculated the shaft center trajectory for a dynamically loaded journal bearing. This method is valid ated with nonlineardynamics analysis of a complex rotor-bearing system. The results show that theproposed method can accurately solving the nonlinear dynamics of complexrotor-bearing system.In addition, axial trajectory of different speeds and oil press ureis studied, the oil stability when the rotation speed and oil pressure changed isanalyzed.