Abstract
ABSTRACTThe results of extensive experimental testing of an aero-engine air-oil separator are presented and discussed. The study focuses on the pressure loss of the system. Oil enters the device in the form of dispersed droplets. Subsequently, separation occurs by centrifuging larger droplets towards the outer walls and by film formation at the inner surface of a rotating porous material, namely an open-cell metal foam. The work described here is part of a study led jointly by the Karlsruhe Institute of Technology (KIT) and the University of Nottingham (UNott) within a recent EU project.The goal of the research is to increase the separation efficiency to mitigate oil consumption and emissions, while keeping the pressure loss as low as possible. The aim is to determine the influencing factors on pressure loss and separation efficiency. With this knowledge, a correlation can eventually be derived. Experiments were conducted for three different separator configurations, one without a metal foam and two with metal foams of different pore sizes. For each configuration, a variety of engine-like conditions of air mass flow rate, rotational speed and droplet size was investigated. The experimental results were used to validate and improve the numerical modelling.Results for the pressure drop and its dependencies on air mass flow rate and the rotational speed were analysed. It is shown that the swirling flow and the dissipation of angular momentum are the most important contributors to the pressure drop, besides the losses due to friction and dissipation caused by the flow passing the metal foam. It was found that the ratio of the rotor speed and the tangential velocity of the fluid is an important parameter to describe the influence of rotation on the pressure loss. Contrary to expectations, the pressure loss is not necessarily increased with a metal foam installed.
Highlights
Aero-engine bearings require a steady supply of oil for lubrication and cooling
Understanding the significance of the various effects and how they depend on the breather configuration, mass flow rate and rotational rotor speed is important for the improvement of future shaft breather designs with respect to the overall pressure loss
This paper presents the experimental results obtained from a rotating aero-engine oil separator
Summary
Aero-engine bearings require a steady supply of oil for lubrication and cooling. Ideally, all of the oil running through the bearings is recycled to minimise the total weight of the oil carried on board. Understanding the significance of the various effects and how they depend on the breather configuration, mass flow rate and rotational rotor speed is important for the improvement of future shaft breather designs with respect to the overall pressure loss. For both configurations with a metal foam (coarse and fine), it was not possible to reach zero rotor rotation for high air mass flow rates because the rotor was set into motion by the swirling flow. The effect of rotational speed will be explained phenomenologically based on the CFD results and on the analytical model derived in the first section
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