An Experimental Study on Droplet Generation in Bearing Chambers Caused by Roller Bearings

The lifetime of aero-engine roller bearings strongly depends on lubrication and particularly on sufficient cooling provided by the oil system of the engine. During the development of advanced engines the overall oilflow has to be minimized to reduce size and weight of oil pipes and pumps. To support this development a fundamental understanding of the complex air/oilflow in bearing chambers is required. Although numerous efforts to characterize the liquid wall films were performed in recent years, only few investigations were carried out to carefully study the droplet generation in bearing chambers under realistic conditions. Therefore, the current research was initiated. Within the scope of this paper, a comprehensive experimental study on the droplet generation by a cylindrical roller bearing was carried out for a wide range of engine relevant conditions. In a first step, the oilflow near the roller bearing was visualized in a model bearing compartment. The results revealed that the pressure difference across the bearing and the design of the bearing support have strong influence on the generation of droplets. Furthermore, the velocity of the droplets was determined by means of stereoscopic particle image velocimetry. Based on these results a significantly improved understanding of the droplet generation caused by roller bearings was derived and compared to the experiments.