The demand for continuous and efficient lubrication in aeroengine bearing assemblies has encouraged the development of scoop based lubrication systems. Using a scooped rotor in conjunction with axial passages within the shaft, a scoop system can provide lubrication to bearings and other components at a different axial location to the oil supply jet, optimizing the use of space.
The capture efficiency of a scoop system is the percentage of oil from the jet that is delivered to the desired end location. It is dependent on a number of factors such as shaft rotational speed, oil jet speed and other geometrical features. In this paper the impact of shaft speed on the capture efficiency of a scoop system is predicted numerically using Computational Fluid Dynamics (CFD). An analytical study has been also carried out to aid the understanding of the system’s behaviour. A simplified 2D geometry is used for the computational domain in the numerical simulations. The Volume of Fluid (VOF) multiphase model has been implemented to simulate the flow of oil and air. The effects of turbulence are modelled using the RNG K-ε turbulence model. Results obtained using CFD are compared to experimental results obtained from tests conducted on the same geometry.
It is evident from CFD and experiments that for a fixed oil jet velocity there is an optimum shaft speed at which maximum capture efficiency is obtained. This is somewhat higher than the threshold value identified by the analytical study at which 100% capture becomes theoretically possible. Maximum capture efficiencies of around 80% are predicted. Some oil is uncaptured because it forms a plume ahead of the scoop tip and deflects outwards and some is initially captured but leaves the scoop through centrifugal effects.
The analytical model suggests that the point of jet strike on the scoop may affect/control losses due to centrifugal effects with more oil being lost when the point of strike is closer to the scoop tip. Pluming losses become more significant at higher shaft speeds because the angle over which oil is captured decreases.
Predicted scoop capture efficiencies obtained using CFD are within 5.5% of experimentally obtained results for the configuration investigated here. Trends in behavior are the same experimentally and computationally highlighting the usefulness of a 2D CFD modelling approach.