Windage Losses in High Speed Gears: Preliminary Experimental and Theoretical Results

Abstract

Power losses in high-speed gears come from the friction between the teeth (sliding and rolling), the lubrication process (dip or jet lubrication), the pumping of a gas-lubricant mixture during the meshing and the losses associated with windage effects. The objective of this paper is to present a number of preliminary experimental and theoretical findings on the prediction of windage losses. Experiments were conducted on a test bench whose principle consists in driving a gear to a given speed and then measuring its deceleration once it has been disconnected from the motor. The transmission between the motor and the rotor is ensured by a friction wheel which also plays the role of speed multiplier. A pneumatic jack either imposes a sufficient contact pressure between the driving wheel and the rotor (transmission of rotation), or is used for separating the parts when the maximum speed is reached. A disk and 4 different gears were tested in the absence of a lubricant at speeds ranging from 0 to 12 000 rpm. Two different theoretical approaches have been developed: i) a dimensional analysis based upon the dimensionless groups of terms which account for the flow characteristics (Reynolds number), the gear geometry (tooth number, pitch diameter, face width) and the speed, ii) a quasi-analytical model considering in detail the fluid flow on the gear faces and inside the teeth. It is found that both approaches give good results in comparison with the experimental evidence and two analytical formulae aimed at predicting windage losses in high-speed gears are proposed.

Numerical Simulation of Oil Jet Lubrication for High Speed Gears

“…The calculation of windage losses is not the objective of this study, but it is calculated by VOF simulation and it is added to the resistant torque due to the oil jet lubrication. The subatmospheric pressure condition leads to a significant reduction of air density; as a consequence the windage torque decreases with respect to the lubrication torque; in fact windage losses are proportional to air density, as presented by Diab et al [16]. The resultant windage torque will be subtracted from the torque calculated in the VOF simulation, in order to evaluate only the contribution due to the oil jet lubrication.…”

Modelling windage power loss from an enclosed spur gear

“…Diab et al [12] presented an experimental study of a single spur gear rotating in air without enclosure. Four spur gears were investigated, with pitch diameters from 144-300mm, face width 30-60mm and modules of 4 and 6.…”

“…Shrouding is a far more promising approach that is already widely used within industry. A number of authors have investigated shrouding for either spur or helical gears [2][3][4][5][6][7][8][9][10][11][12][13] and this study builds on previous work, investigating the effects of shrouding and tooth form modification. CFD data is compared with published experimental data where possible.…”

“…Whilst equations are available to predict the windage power loss of gears, all are based on experimental correlations [2][3][4][5][6][7][8][9][10][11][12][13] and are restricted in application in many cases. This means that designers have, at best, an estimate of the WPL and in addition, cannot take their design too far from previous, successful designs, thus limiting the design envelope.…”

Computational Fluid Dynamics Simulations and Experiments for Reduction of Oil Churning Loss and Windage Loss in Aeroengine Transmission Gears

“…In addition, oil churning and windage losses in a bevel gear have been studied with various shroud shapes [3]. However, previous CFD simulations [4][5][6] have only dealt with the air in the shroud. It should be noted that the experimental visual ization of flow is difficult due to the very complex flow of oil and air around gears that rotate at high speeds; thus, computational fluid dynamics (CFD) simulations should prove effective for this type of problem.…”