Experimental Investigation of the Oil Jet Heat Transfer for an Aero Engine Gearbox

Geared turbofan engines have the potential to propel future civil aircraft engines more efficiently. A planetary gearbox between the low-pressure turbine and the fan enables the operation of both components at their respective optimum rotational speeds. This makes it possible to achieve higher bypass ratios and thus a better propulsion efficiency. A crucial part of the planetary gearbox design is the cooling and lubrication of the gears. Sufficient heat removal from the gear tooth flanks is necessary to ensure reliable operation without the risk of gear failure through pitting or scoring. Fast rotating and highly loaded gears are cooled with impinging oil jets according to current design guidelines. This impingement cooling process comprises a complex, multi-phase flow with heat transfer. Previous experimental, numerical and analytical investigations have shown that the cooling process depends both on the highly unsteady liquid flow dynamics and on the heat conduction in the oil film formed on the gear tooth flank. In this study, the gear is replaced by a cylinder in order to be able to study the impingement cooling on a rotating surface without the influence of unsteady flow phenomena. ... mehrA hollow cylinder is instrumented with 42 thermocouples across the surface, which are all connected to a telemetry system. A single oil jet is directed radially onto the outer cylinder surface. The measured temperatures are subsequently corrected using a new algorithm to reduce systematic measurement errors without distorting the data. The corrected temperatures are used to calculate the Nusselt number distribution across the cylinder surface by means of a finite element analysis. A parameter study is performed to identify the influence of the parameters oil flow rate, oil viscosity and rotational speed of the cylinder on the heat transfer. The fundamental results of the present study enable a better understanding of the heat transfer on impingement cooled cylinders and spur gears.