NDLI: Windage Power Losses From Spiral Bevel Gears With Varying Oil Flows and Shroud Configurations

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Johnson, Graham Chandra, Budi Foord, Colin Simmons, Kathy
Copyright Year	2008
Abstract	In many aero-engines the power to drive accessories is transmitted through high speed bevel gears in a chamber in the center of the engine. The windage power loss (WPL) associated with these gears makes a significant contribution to the overall heat generation within the chamber. Shrouding the gears provides an effective method of reducing this WPL and managing the flow of lubricating oil. Experimental and computational programs at the University of Nottingham Technology Centre in Gas Turbine Transmission Systems are providing an improved understanding of shroud performance and design. This paper presents results from a pair of shrouded meshing gears run at representative speeds and oil flow in a rig with speed and torque measurement. A previously published study of a single bevel gear operating in air [1] found a reduction in torque of up to 70% from shrouding. In this work the addition of oil and the pinion gear did not lead to high torque due to the build up of oil under the shrouds, but the reduction in torque due to fitting the shrouds is significantly less than was found for the same gear in air alone. In order to isolate the various parameters, further testing with a single gear was carried out. A fully (360 degree) shrouded gear shows a big improvement over an unshrouded gear when running in air alone, but much of this benefit disappears as soon as a very small amount of oil is introduced under the shroud. This implies that the oil is recirculating under the shroud. Increasing the oil flow beyond this initial level increases the torque by the amount required to accelerate the oil mass flow up to the peripheral speed of the gear. Providing a full width slot in the shroud downstream of the oil jet allows the oil to escape without any recirculation and restores much of the benefit of the shroud. Further insight into the oil behavior is obtained from torque measurements and observations through a transparent shroud and with various slot configurations. Video observation shows evidence of a vortex flow under the shroud that carries some of the oil towards the inner diameter of the gear. The three main windage contributors, air alone, recirculation of oil under the shroud and acceleration of the feed oil are quantified and methods for achieving the optimum design are discussed.
Sponsorship	International Gas Turbine Institute
Starting Page	1415
Ending Page	1421
Page Count	7
File Format	PDF
ISBN	9780791843147
DOI	10.1115/GT2008-50424
e-ISBN	0791838242
Volume Number	Volume 4: Heat Transfer, Parts A and B
Conference Proceedings	ASME Turbo Expo 2008: Power for Land, Sea, and Air
Language	English
Publisher Date	2008-06-09
Publisher Place	Berlin, Germany
Access Restriction	Subscribed
Subject Keyword	Torque Transparency Spiral bevel gears Aircraft engines Torque measurement Flow (dynamics) Engines Design Fittings Heat Gears Gas turbines Bevel gears Lubricating oils Vortex flow Testing
Content Type	Text
Resource Type	Article

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