Relevance of the thermoelastohydrodynamic model in the analysis of a plain journal bearing subjected to severe operating conditions

Abstract

Bearings, which were initially designed to support loads, are nowadays being used more and more in machines and most of them are subjected to severe operating conditions as far as temperature or minimum film thickness are concerned. This can be considered as the result of the increases in speed and load, which increase the dissipated power in the lubricant, and also the temperature, thus significantly modifying the lubricant characteristics and bearing performance. This leads, on the one hand, to a decrease in the lubricant viscosity, and therefore the load capacity, and, on the other hand, to mechanical and thermal deformations of the contact surfaces which can, under severe operating conditions, be greater than the minimum film thickness. The present study investigates the relevance of taking into account the deformations and how they can influence bearing performance prediction. The operating conditions are variable, with the radial load ranging up to 150kN and the rotational speed ranging up to 15000r/min. The thermoelastohydrodynamic (TEHD) model is compared to an existing thermohydrodynamic (THD) model in order to find the point at which it is necessary to take into account deformations in the numerical simulation and thus ensure good prediction of bearing behaviour. Under severe conditions, the THD model was found not to give good results for bearing performance and geometry; i.e. the hydrodynamic pressure can be dangerously overestimated, the minimum film thickness can be underestimated and the bearing operating radial clearance can be increased by over 10 per cent.