In some aero-engine applications a spiral bevel gear is mounted in a bearing chamber. The windage power losses (WPL) associated with the gear make a significant contribution to the overall heat generation within the bearing chamber and a potential method of WPL reduction and lubrication/cooling oil management is to shroud the gear. At the University of Nottingham Technology Centre in Gas Turbine Transmission Systems experimental and computational techniques are being applied to enhance understanding of shroud performance and design. This paper presents results from the first stage of the investigation in which the windage losses associated with rotating an unmeshed spiral bevel gear in air have been studied. The potential to reduce gear WPL by shrouding is clearly demonstrated with the WPL for the shrouded gear reduced on average by 75% for clockwise rotation and by 70% for anticlockwise rotation. Given the physical similarity between a shrouded gear and a centrifugal fan an attempt was made to characterize the performance of the shrouded gear in a similar manner to that used for a centrifugal fan i.e. as a function of the mass flow rate of air flowing through the shroud. It is demonstrated that in many aspects the gear performance was analogous to centrifugal fan behavior. It is further demonstrated that fan design approaches could be adopted to inform the detail of the shroud design and to translate test rig performance to different operating conditions.
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