The Effect of Pads Number and Their Tilt Angles on the Bearing Stiffness

Abstract

In this work a plain (conventional) and a tilted bad bearings are analyzed and studied (both have the same dimensions and work conditions). Three, four and five pads models are studied. The pads are fixed circumferentially in a manner each two close pads are separated with an angle that is the same for all the close pads. Each pad is pivoted in its trailing edge and is facilitated to be tilted around this pivot with small angles. This study was achieved for three values of tilting angles. These angles are, 0.01o, 0.011o and 0.012o. Two dimensions' form of Reynolds equation is used and solved numerically then the stiffness coefficients had been calculated. A comparison had been done between the stiffness coefficients values for the two models (tilted pads and conventional bearings). The results of this comparison was found that (for n = 0.4), are, +28%, +275%, +270 % and -100% for Ksr, Krr, Kss and Krs respectively. It was noticed that the values of the principal coefficients Krr and Kss are increased significantly while the cross coupling coefficient, (Krs) is decreased significantly and (Ksr) is increased slightly. And this is a positive sign for stability improvement. Also it was found that increasing the tilt angle (delta) cause an increase of the stiffness coefficients values. These increases (for n = 0.4 and changing the tilt angle from 0.010 to 0.011 then to 0.012 respectively) are, Krr=+50%, +47%, Kss = +40%, +32%, Ksr = +33%, +42%, and Krs = +15%, +20%. And since increasing the values of the cross coupling coefficients make the bearing stability worse, so increasing the tilt angle is not a preferable method for improving stability. Changing the number of pads is a better solution and it was found that three pads bearing is the best among them.