Flow Distortion Measurements in Convoluted Aeroengine Intakes

The unsteady flowfields generated by convoluted aeroengine intakes are sources of instabilities that can compromise the performance of the downstream turbomachinery. Hence, there is a need for synchronous high-spatial-resolution measurements that will allow a greater understanding of the aerodynamics. In this work, stereo particle image velocimetry is used in a new application to characterize the distorted flow at the outlet of complex intakes. A suite of measurements and analyses for two S-duct configurations across a range of inlet Mach numbers is presented. The work demonstrates the feasibility of using stereo particle image velocimetry techniques for determining the flowfield at the exit of convoluted intakes with a higher spatial resolution than typical pressure measurements. Analysis of the distortion descriptors quantifies the dependency upon the S-duct configuration and highlights that the more high-offset duct generates greater levels of swirl distortion relative to the low-offset configuration. Distortion maps show that the flow is highly unsteady with a characteristic switching of the swirling flow. The results provide a new dataset that shows that the conventional assessments based on time-averaged data substantially underestimate the swirl distortion level and that the less frequent distortion events give rise to more potentially significant threats to the compression system.