Scavenge Performance of an Optimized Shallow Sump at Various Flow Conditions

Abstract

Oil scavenge flow in aero-engine bearing chamber remains largely a challenging problem for many engine designers. Research campaign on scavenge flow has been conducted by G2TRC – Gas Turbine and Transmissions Research Centre (previously Rolls Royce University Technology Centre in Gas Turbine Transmission Systems) at the University of Nottingham. It was recognized that a deep sump performs better than shallower one due to its ability to “shield” the collected oil in the sump from the shaft windage thus reducing the amount of oil being picked up by the bulk air rotation. However, such a deep sump design cannot be employed in some engines and especially at certain locations where space is limited. A parametric study combined with phenomenological approach on shallow sump geometry has been conducted and presented in the previous publication where a certain optimized shallow sump variant was proposed depending on whether the flow in the chamber is wall film dominated or airborne droplets dominated. The parametric phenomenological approach was employed since it can be done relatively quicker than typical data gathering through an experiment. However the approach relies on qualitative interpretation of the flow features, and its application in bearing chamber flow research has never been validated before. This paper presents the results of quantitative measurements of residence volumes of an optimized shallow sump variant identified in the parametric phenomenological study. Comparison was then made with the residence volumes of some existing engine sumps. It was found that the optimized shallow sump for wall film dominated flow has lower residence volumes compared to some existing engine sumps. In some cases, the residence volume can be reduced by up to 75%. An optimized shallow sump variant for airborne droplets dominated was also identified in the previous parametric phenomenological study, although the residence volume measurement is yet to be conducted. The optimized shallow sump for wall film dominated flow was also identified as a good sump regardless of the flow regime. However when it was tested in airborne droplets dominated flow, its residence volumes are higher than some of the existing engine sumps. This highlights the importance of considering the flow regime in the bearing chamber in any attempt to optimize a sump geometry.