Transient mixed-lubrication analysis of low-viscosity lubricated bearings under impact load with consideration of turbulence

For heavy-duty bearings with low-viscosity lubricant, asperities may contact near the minimum nominal film thickness, while turbulence may develop in the area with large film thickness. When bearings encounter transient impact or unsteady loads, the influence of turbulence and surface roughness is relatively complex. To investigate transient lubrication and dynamic characteristics of mixed-lubricated bearings with turbulent flow, a transient mixed-lubrication model considering turbulence is proposed in this paper. A transient generalized average Reynolds equation is derived based on the Ng-Pan turbulence model. The transient journal center positions are obtained by solving the journal's dynamic equation. The numerical procedure is established. Based on the proposed model, the effect of turbulence, surface roughness, and transient impact load direction as well as the magnitude on transient lubrication and dynamic characteristics of mixed-lubrication bearings is analyzed. The results show that turbulence increases the transient minimum nominal film thickness and may decrease the transient friction force in the mixed-lubrication regime. Surface roughness modifies the dynamic trajectory of the journal center and increases both the transient minimum nominal film thickness and the friction force in the mixed-lubrication regime. The impact load direction significantly affects transient characteristics of the bearing. An increase in the load-deflection angle destabilizes the bearing operation state.