Rotor response to unbalanced load and system performance considering variable bearing profile

Abstract The demand of the current industrial applications to high power generation results in a further increase in the rotating machinery speed which in itself may cause unstable oscillations. Unbalanced excitation and shaft deviation represent significant challenges that are faced by the designers and operators of the rotor-bearing systems, which negatively affects the general system performance. This work investigates the rotor response to an unbalanced load for a range of bearing ratios. The influence of using a bearing with a variable profile on the characteristics of the system is also investigated. Five bearing’s length-to-diameter ratios are considered in the analysis to examine the generality of the results using different profile parameters. The finite difference method is used in the numerical solution and a 3D deviation model is incorporated in the analysis. The rotor response is obtained by using the fourth-order Runge-Kutta method. Results show that the journal-bearing performance can be improved significantly for the whole considered range of the length-to-diameter ratio by adopting the relevant combination of the design parameters for each ratio. The levels of friction and maximum pressure at deviation levels of 0.52 and L / D = 1 are reduced by 7.02 and 26.9%, respectively, and similar trends have been obtained for the other bearing ratios. More importantly, the lubricant thickness level is enhanced to a large extent as a result of using the variable bearing profile despite the presence of large shaft deviations. This important outcome maintains a safe system operation under extreme operating conditions.