The geared turbofan is a promising concept for future civil aircraft jet engines on the way to green air traffic. With the introduction of a gearbox between the low-pressure turbine and the fan, both components can rotate at their respective optimum speed. The geared turbofan offers the potential of lower specific fuel consumption as well as jet engine noise reduction. This high-speed gearbox, usually installed as a planetary arrangement, needs to transmit high loads at maximum efficiency in limited installation space. The usual way of cooling and lubrication is by oil jet impingement. To ensure an optimum gearbox design regarding efficiency and safe operation, the thermal behavior of the gears needs to be understood thoroughly. The heat generated by the meshing processes is dissipated by oil impingement cooling. While the field of Elastohydrodynamics yields good results for the heat generation process, no validated model for the impingement cooling process is available in literature. In this study, an analytical model of the impingement cooling process is developed and validated against experimental data. First, the surface area of the oil film on the gear tooth flank formed by the impinging oil jet is calculated. Secondly, the heat transfer from the gear tooth flank to the oil film is determined. The fluid motion of the oil film is modeled as an oil film flung off the gear tooth flank by centrifugal forces. In addition to the film flow, the presented model takes into account the temperature dependence of the viscosity of the oil and the initial oil film height. The effect of a lubrication oil film on the gear tooth flank before the oil jet impinges is included and its effect on the heat transfer is assessed. A parameter study of the input parameters oil flow rate, rotational speed and oil jet angle on the heat transfer is presented. An increase in heat transfer is observed for an increase in oil flow rate as well as for a decrease in rotational speed. The oil jet angle has a relatively small effect on the heat transfer mechanism. The analytical model agrees well with experimental results over the entire range of investigated operating conditions. It can now be applied as a fast efficient tool for the design of gearboxes with impingement cooled spur gears.


Analytical Model for the Heat Transfer in Impingement Cooled Spur Gears

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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