Numerical Simulation of Oil Jet Lubrication for High Speed Gears

Abstract

The Geared Turbofan technology is one of the most promising engine configurations to significantly reduce the specific fuel consumption. In this architecture, a power epicyclical gearbox is interposed between the fan and the low pressure spool. Thanks to the gearbox, fan and low pressure spool can turn at different speed, leading to higher engine bypass ratio. Therefore the gearbox efficiency becomes a key parameter for such technology. Further improvement of efficiency can be achieved developing a physical understanding of fluid dynamic losses within the transmission system. These losses are mainly related to viscous effects and they are directly connected to the lubrication method. In this work, the oil injection losses have been studied by means of CFD simulations. A numerical study of a single oil jet impinging on a single high speed gear has been carried out using the VOF method. The aim of this analysis is to evaluate the resistant torque due to the oil jet lubrication, correlating the torque data with the oil-gear interaction phases. URANS calculations have been performed using an adaptive meshing approach, as a way of significantly reducing the simulation costs. A global sensitivity analysis of adopted models has been carried out and a numerical setup has been defined.

CFD study of oil-jet gear interaction flow phenomena in spur gears

“…5c, the generated oil film is spreading on the flank and parts of the oil are flung off directly during the impact process, which is then further supported by the acting centrifugal forces. The predicted results agree well with the work by Fondelli et al (1,12) and Keller et al (2,13) The illustration of the observable flow phenomenology during the OGI in Fig. 5 shows the complex structure of the prevailing two-phase flow -in its geometric shape and in its temporal evolution.…”

“…On the confinement in radial direction of the outer zone, a pressure outlet is applied. Gravity is omitted, since its effect is negligible (1,2) . The setup contains two mesh interfaces.…”

“…Consequently, the oil is flung off by centrifugal forces. Fondelli et al (1) and Keller et al (2) present characteristic non-dimensional groups. They show that while the impingement and spreading is mainly driven by inertia forces, the film motion is driven by centrifugal, viscous, and to a lesser extent by surface tension forces.…”

“…A sensitivity study illustrated the strong influence of mesh resolution and different AMR strategies on the simulation results. In a further work by the authors (1) , the isothermal setup was used to investigate the influence of the oil-jet inclination angle on the resistant torque. A challenging aspect about the OGI simulation is the incorporation of the gear rotation and gear meshing.…”

Research on lubrication characteristics of asymmetric helical gear based on CFD method

“…The transient lubricant film thickness, pressure and friction coefficient characteristics of the spur gears were compared under different carrier fluid ferrofluids. Fondelli et al 15 studied fluid dynamic losses through CFD simulations. Fluid dynamic losses are mainly related to viscous effects, and they are directly related to lubrication methods.…”