Effect of radial clearance on the dynamic behavior of adjustable journal bearings in turbulent and laminar flow regimes

Abstract

Radial clearance critically affects journal bearing performance, specifically the lubrication performance. This study investigates the lubrication characteristics of a journal bearing with adjustable radial clearance and compares the dynamic behavior of the bearing under laminar and turbulent flow regimes. The adjustable bearing exhibits two states of oil film pressure at different radial clearances. When the radial clearance is reduced from 100%cr to 80%cr, the oil film pressure is present only on the lower bearing bush; after being reduced to 70%cr, the upper bearing bush achieves effective lubrication; and after reduction from 70%cr to 30%cr, the oil film pressure increases more than six-fold. The turbulent flow model of the clearance adjustable bearing is then established considering the lubricant flow state, and the turbulence correction factors for different flow states are calculated. The journal bearing exhibits better lubrication characteristics under laminar than under turbulent flow conditions, and in some operating conditions, the stable velocity range calculated according to laminar flow theory may become unstable in turbulent flow conditions. Therefore, applying turbulence assumptions to design the operating speed range of rotating machinery under such conditions yields a greater safety threshold, which can reduce the risk of instability. The stability of the rotor bearing system is closely related to the radial clearance, and reducing the radial clearance will improve the stability of the system. In the turbulent flow state, the oil film pressure changes drastically, thus reducing the system stability. Moreover, the larger the radial clearance of the bearing, the more prominent the turbulence effect. Thus, reducing the bearing clearance prevents drastic changes in oil film pressure and improves the stability of the system.