CFD Study Exploring Jet Configurations and Jet Pulsing for an Aeroengine Scoop-Based Oil Delivery System

Abstract

With reduction of gas turbine core size, clearances between internal components are reduced and directing oil jets for bearing lubrication becomes more difficult. If direct access to the bearings or scallops is impeded, the inclusion of oil scoops becomes highly desirable for lubricant supply. With a scoop-based system oil is targeted at a scooped rotor, collected and fed along axial passages and delivered at a different axial location thus enhancing design opportunities. The proportion of oil from the supply jet retained by the scoop system is an important design parameter that can be characterised by the concept of capture efficiency. Previous investigations have focussed on a proposed scoop device’s operating conditions and oil jet configurations; this study proposes new methods of utilising the jets to improve scoop capture efficiency. A parametric study of a 2D scoop geometry was conducted using the Computational Fluid Dynamics (CFD) software ANSYS Fluent. The simulation utilised the Volume of Fluids (VOF) approach for multiphase modelling and the k-ω SST model to account for turbulence. In the configuration studied the oil was supplied via two nozzles separated by 10 degrees circumferentially. An uneven flow rate between two oil jets in tandem allowed for the identification of jet interaction effects. A transition in capture efficiency responses was also highlighted between shallow and steep jet angles. The knowledge of individual jet behaviour may immediately improve existing tandem jet configurations. Further, the concept of pulsing the jets was investigated, the idea being initiated following observation of high speed imaging of a scoop system tested experimentally. The imaging shows that most of the uncaptured oil is deflected or splashed following interaction with the scoop. Turning the oil off for part of the cycle potentially reduces or eliminates this. By defining and implementing an optimised time scheme for the pulsation of a single jet, the capture efficiency was improved by 10%. Compensating for the associated flow rate reduction by increasing the jet velocity resulted in a further 5% increase in capture efficiency. The development of pulsed jets for practical applications has the potential to significantly improve oil scoop capture efficiency.