Reduction of Power Losses in Bearing Chambers Using Porous Screens Surrounding a Ball Bearing

Trends in aircraft engine design have caused an increase in mechanical stress requirements for rolling bearings. Consequently, a high amount of heat is rejected, which results in high oil scavenge temperatures. An RB199 turbofan bearing and its associated chamber were modified to carry out a survey aiming to reduce power losses in bearing chambers. The test bearing was a 124 mm PCD ball bearing with a split inner ring employing under-race lubrication by two individual jets. The survey was carried out in two parts. In the first part, the investigations were focused on the impact on the power losses in the bearing chamber of the operating parameters, such as oil flow, oil temperature, sealing air flow, bearing chamber pressure, and shaft speed. In the second part, the investigations focused on the reduction of the dwell time of the air and oil mixture in the bearing compartment and its impact on the power losses. In this part, porous screens were introduced around the bearing. These screens would aid the oil to flow out of the compartment and reduce droplet-droplet interactions as well as droplet-bearing chamber wall interactions. The performance of the screens was evaluated by torque measurements. A high-speed camera was used to visualize the flow in the chamber. Considerable reduction in power loss was achieved. This work is part of the European Research programme GROWTH ATOS (Advanced Transmission and Oil Systems).