A STUDY ON THE PERFORMANCE OF HYDROSTATIC/HYBRID JOURNAL BEARING CONSIDERING COMBINED INFLUENCE OF WEAR AND MICROPOLAR LUBRICATION

Abstract

Bearings are used extensively- in all machinery to support loads. The bearing performance plays a crucial role in functioning of chemical, petrochemical, automotive, nuclear applications, power generation, aerospace turbo machinery and .process industries all over the world. Owing to the fast technological developments, during the last few decades, the operating conditions of the machines are becoming very stringent, exact and more demanding. Therefore, the bearing are required to be designed on more realistic data so that to meet the demanding requirement. The flow behavior of the lubricant plays a crucial role on bearing performance. Generally, the bearings are designed based on the assumption of Newtonian behavior of lubricant. However in modern lubricant, polymer additives are added in high percentages making the behavior of lubricant non-Newtonian [33-35] and therefore microcontinuum theories must be used to accurately predict bearing performance. Further, as the bearing is expected to run over a number of cycles during its lifetime, it is subjected to several start/stop operations. These transient periods causes the bearing bush to wear out and significantly affects the bearing performance. A thorough scan of literature reveals that there are very few regarding the micropolar lubrication and wear for the multirecess journal bearing. Also, to the best of author's knowledge no study has been reported in literature regarding the performance of multirecess journal hydrostatic/ hybrid journal bearing by considering combined influence of wear and micropolar lubrication. Therefore, the present dissertation work is aimed at formulating a mathematical model to study the performance of multirecess hydrostatic/hybrid journal bearing system operating with micropolar lubricant by considering the influence of wear and thereby bridging the gap in literature. The change in the geometry caused due to wear during transient (start/stop) operations has been modeled using Durfrane's abrasive wear model [61]. The flow behavior of the lubricant containing additives and containments has been modeled as micropolar fluid [11]. The modified Reynolds equation governing the flow of micropolar lubricant in the clearance space of bearing has been solved using an iterative scheme based on FEM and Newton-Raphson method by taking into account the change in bearing geometry due to effect of wear. The code developed to analyze the performance of worn hybrid/hydrostatic journal bearing system operating with micropolar lubricant has been validated by comparing the simulated results from present study with several previously published papers [24,63,64,49 and 53]. The simulated results from the present study have been presented for a wide range of wear depth parameter and micropolar parameters by considering various flow control devices i.e. membrane, orifice and capillary. The results have also been presented for a hydrostatic/hybrid journal bearing system with different geometric shapes of recess operating with micropolar lubricant. The simulated suggests that it is imperative to account for the effect of wear in order to predict the performance of the bearing accurately. Further, it has been observed that in general the as the micropolar effect of lubricant increase the performance of the enhanced as compared to Newtonian lubricant. It has been also noticed that the effect of wear on the performance of bearing lubricated with micropolar lubricant is. significantly affected by the loading arrangement and also by the type of restrictor.