Stability of rotor supported on powder lubricated journal bearings with surface pockets

Abstract

Conventional oil lubricated journal bearings experience a degradation in the lubrication properties of oil at high temperatures thereby making the use of oil lubricants impractical in a hot working environment. Under these conditions, powder lubricants can be used for the successful operation of the rotor-bearing system. Whirl instability is a serious problem for rotors supported on journal bearings which restrict the system to be operated at high speeds. Surface modifications in the form pocket in the bearing can be used to improve the performance. A sudden change in film thickness caused by the presence of pocket in the bearing will generate hydrodynamic pressure which will support the external load and may influence the stability of the rotor supported on such bearings. The objective of this paper is to explore the stability characteristics of powder lubricated journal bearings employing pockets of different shapes (rectangular, trapezoidal, elliptical, and parabolic). It is observed that though the pocket of all shapes increases the whirl stability of a rotor-shaft system, the rectangular shape is the most effective among all. Therefore, such bearings may be given a rectangular pocket to increase the stability of rotors.

Performance improvement of foil air journal bearing employing micro-pocket and textures on top compliant surface

“…It is understood that this has happened due to spreading of film pressure over larger area along the circumferential direction as compared to cases as discussed in section 6.2. A similar observation has been reported in paper [45]. Moreover, the pocketed bearing results in reduced cross-coupled stiffness values, which is essential for decreasing the instability of a rotor-bearing system.…”

“…Moreover, these innumerable micro-geometries of textures trap the debris/contaminants and supply the oil/grease for smearing at the interface under the mixed-lubricating condition [20,21]. It has been observed that if the depth of micro-geometries/dimples happens very close to oil minimum film thickness, then the best results can be achieved [37][38][39][40][41][42][43][44][45][46].…”

Influence of Bearing Wear on the Stability and Modal Characteristics of a Flexible Rotor Supported on Powder-Lubricated Journal Bearings

“…[17,18]. For a finite bearing, coefficients can be evaluated numerically using the perturbation technique [19,20]. Negatively cross-coupled stiffness tends to destabilize the whirling of rotors due to a tangential force acting in the direction of the whirl orbit.…”

“…Stiffness and damping coefficients of the powder film are obtained using the finite perturbation technique [19,20]. With very small perturbations of displacements (∆X, ∆Y) and velocities (∆ .…”