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Hybrid bearings have been used in high-speed machine tools due to their inherent advantages of low temperature rise, high load-carrying capacity, and high stability. The objective of this study is to investigate the influence of turbulence and thermal effects on the performance of water-lubricated hybrid bearings with circumferential grooves and stepped recesses used to support high-speed spindles. The governing equations are solved using the finite element method with appropriate boundary conditions. A bulk-flow thermohydrodynamic model has been developed incorporating the turbulence effect. The results indicate that the turbulence effect appreciably affects the bearing performance. Besides, the thermal effect should also be taken into account especially when the rotating speed is high. The study gives a useful guide for the future hybrid bearing design and operation of high-speed spindles supported by water-lubricated hybrid bearings.

Bearings are key components in high-speed and highprecision machine tools. Temperature rise and stability are significant for a rotor-bearing system in a high-speed spindle. This study proposes a water-lubricated hybrid bearing with circumferential grooves and stepped recesses to lower the temperature rise and improve bearing stability. A bulk-flow thermohydrodynamic model is developed to predict the static performance and stability of the bearing. A comparison of the results confirms the validity of the model and the improved characteristics of the hybrid bearing. A sensitivity analysis is conducted to quantify the influence of recess sizes on bearing performance. The discussion defines the key parameters of bearing performance and provides a useful guide for the optimal design of hybrid bearings.

Rotor stability and rotation accuracy, which are highly dependent on the dynamic coefficients of supporting hybrid bearings, are two important issues of high-speed water-lubricated spindles. To improve the spindles' performance, the dynamic coefficients of high-speed water-lubricated hybrid bearings were experimentally identified by the noncontact harmonic excitation method and the additional unbalance excitation method, respectively. Comparisons between experimental results and theoretical predictions were made. The experimental technique and the identification model were validated to be effective. Besides, the influence of supply pressure and rotating speed on dynamic coefficients was also presented. As for different operating conditions, valuable guides were provided to investigate the dynamic performance of high-speed and ultra-high-speed spindles.

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