Turbulence Effects on the Dynamic Characteristics of Non-Circular Journal Bearings Under Large Sommerfeld Number Conditions

Turbulence and instability problems are unavoidable challenges for fluid film bearings as rotation speed continues to rise. This paper investigates the effect of turbulence on the dynamic characteristics of two non-circular journal bearings, hybrid two-lobe bearing (TLB) and hybrid three-step recess bearing (TSRB), under large Sommerfeld number conditions. The linear perturbation method and nonlinear trajectory method are employed in this work. The bearing stiffness coefficients, damping coefficients, and threshold speed are determined by solving the perturbed Reynolds equation using the finite element method. Additionally, the bearing nonlinear trajectories are obtained by solving the motion equation and the dynamic Reynolds equation simultaneously. The threshold speed and trajectory spectrum are utilized to evaluate the bearing dynamic characteristics, and the results derived from laminar and turbulence models are compared. The research on those two different types of bearings has yielded a consistent conclusion: under large Sommerfeld number conditions, the onset of turbulence significantly enhances both the stiffness and damping coefficients of the bearings, as well as the onset speed for the appearance of half-frequency components in the trajectory. The findings suggest that turbulence lubrication is beneficial for improving the dynamic characteristics of these non-circular bearings.