Hurrell, Michael J. | Search NASA

NASA NTRS2019

Swept Volume Approach for the Characterization of Pumping Loss of Shrouded Meshed Cylindrical Gears

High speed rotorcraft transmissions are subject to load-independent power losses consisting of drag and pumping loss. Tightly conforming shrouds enclosing the transmission gears are often incorporated to reduce the drag component of the total load-independent losses. However, tightly conforming axial shrouding can result in an increase in the pumping loss component. Quantifying the pumping loss of shrouded gear transmissions has been the subject of many studies. This study presents a new approach for estimating pumping loss based on the concept of swept volume borrowed from the positive displacement pump and compressor industry. In this study, pumping loss of shrouded gear transmissions is considered to be related to the swept volume of the gear sets and the downstream flow resistance created by the shroud clearances. The drag loss and pumping loss of a spur gear pair have been determined through testing using the NASA Glenn Research Center Gear Windage Test Facility. The results from this testing have been compared to theoretical results using the formulations presented in this study. Good correlation exist between the test pumping power loss and the predicted pumping power loss for tightly conforming axial shroud configurations.

Hurrell, Michael J.↗

NASA NTRS2017

Experimental Investigation of Shrouding on Meshed Spur Gear Windage Power Loss

Windage power loss in high-speed gearboxes results in efficiency losses and increased heating due to drag on the gear teeth. Test results for meshed spur gear windage power loss are presented at ambient oil inlet temperatures, both with and without shrouding. The rate of windage power loss is observed to increase above a gear surface speed of 10,000 feet per minute (51 meters per second), similar to results presented in the literature. Shrouding is observed to become more effective above 15,000 feet per minute (76 meters per second), decreasing power loss by 10 percent at 25,000 feet per minute (127 meters per second). The need for gearbox oil drain slots limits the effectiveness of shrouding in reducing windage power loss. Windage power loss is observed to decrease with increasing gearbox temperatures and to increase with oil flow. Windage power losses for unshrouded meshed spur gears are 7 times greater than losses determined from unshrouded single spur gear tests. A 6- to 12-times increase in windage power loss is observed in the shrouded meshed spur gear data compared with shrouded single spur gear data. Based on this preliminary study, additional research is suggested to determine the effect of oil drain slot configurations, axial and radial shroud clearances, and higher gear surface speeds on windage power loss. Additional work is also suggested to determine the sensitivity of windage power loss to oil temperature and oil flow. Windage power loss for meshed spur gears tested in both the shrouded and unshrouded configurations is shown to be more than double versus windage power loss for the same spur gears run individually in the same shroud configurations. Further study of the physical processes behind these results is needed to optimize gearbox shrouds for minimum windage power loss.

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NASA NTRS2011

Initial Experiments of High-Speed Drive System Windage Losses

High speed gearing performance is very important to the overall drive system efficiency. Certain losses such as gear meshing and bearing drag can be minimized by design changes such as pressure angle of the gears and the geometry and type of bearings being used. One component that can have a large effect on the overall performance of high-speed drive systems is the parasitic drag known as gear windage. This loss mechanism is not well understood and minimizing this component is usually accomplished through much trial and error. The results presented in this paper will document some of the design parameter effects on the amount of windage losses. A new test facility at NASA Glenn has been assembled to systematically study the design variables. Results from recent tests will be presented. The tests are for a single gear, with and without lubricants, and some initial studies using shrouds.

Handschuh, Robert F.↗

NASA NTRS2010

Initial Experiments of High-Speed Drive System Windage Losses

High speed gearing performance is very important to the overall drive system efficiency. Certain losses such as gear meshing and bearing drag can be minimized by design changes such as pressure angle of the gears and the geometry and type of bearings being used. One component that can have a large effect on the overall performance of high-speed drive systems is the parasitic drag known as gear windage. This loss mechanism is not well understood and minimizing this component is usually accomplished through much trial and error. The results presented in this paper will document some of the design parameter effects on the amount of windage losses. A new test facility at NASA Glenn has been assembled to systematically study the design variables. Results from recent tests will be presented. The tests are for a single gear, with and without lubricants, and some initial studies using shrouds

Handschuh, Robert F.↗