The Dual Drive Booster (DDB) is a novel concept aimed at improving the performance of 2-shaft turbo-fan engines. The DDB concept relies on a high speed epicyclic gearbox to extract power from both the LP and HP shafts and drive the booster compressor. The DDB has also been shown to permit high power extraction from the engine without the large working line excursions which usually limit this. Efficient scavenging of the lubrication oil to prevent churning and heat generation is a requirement of such gearboxes and this paper aims to investigate performance of the oil scavenge system of a typical DDB gearbox.
Efficient scavenging of oil is essential to eradicate the risks that may arise when oil resides in the gearbox for prolonged durations. Longer residence times of oil in the gearbox can lead to rapid oil degradation. Simulations were conducted on a previously optimized geometry and the work in this paper focuses on investigating the effect of different operating conditions on scavenging performance. The effect of attitude, altitude and the inlet flow rate of oil have been simulated to understand their influence on the oil flow behaviour. Emphasis is given on the predicting potential oil churning, recirculation and pooling behaviours in the scavenge chamber that encloses the gear box.
Numerical Investigations are carried out using ANSYS Fluent. The Volume of Fluid (VOF) model is employed to model the multiphase flow arising between air and oil in the system. Validation against published experimental data for similar flow regimes and mesh independency tests were also carried out. Results indicate that the scavenging performance is not affected significantly under the various operating conditions and scenarios that were investigated. This is because the effects of the windage outweigh the effects caused by the different operating conditions that are imposed to the scavenge chamber. The windage in the system drives the oil efficiently out from the chamber with the aid of the tangential sump. Oil is distributed in an axially central section of the chamber and the total residence mass of oil is compared and is under 0.5 kg for all of the cases presented in this paper.