MacManus, David G.Tanguy, Geoffrey2023-01-182023-01-182018-08https://dspace.lib.cranfield.ac.uk/handle/1826/18982Complex aero-engine intakes for embedded propulsion systems are expected to play a major role in the next generation of aircraft. However, convoluted intake diffusers can lead to the development of distorted flows with high levels of unsteady total pressure and swirl distortion. This may exceed the tolerance level of a given engine and lead to compressor surge and performance degradation. Historically, flow control devices were used to reduce the distortion to acceptable levels for the engine. However, the effect of flow control devices on the important unsteady flow field distortion has received little attention. Conventionally, flow distortion assessment for an intake relies on a limited number of time dependent total pressure measurements and even fewer steady swirl measurements at the Aerodynamic Interface Plane (AIP). However, these conventional measurement techniques have a relatively low spatial resolution and the lack of unsteady swirl data are insufficient to capture the characteristics of the unsteady distortion for convoluted intakes. This work presents the assessment of the unsteady distortion for two representative S-ducts as well as the impact of vortex generator flow control devices. The flow field at the AIP was mainly assessed with Stereo-Particle Image Velocimetry which provided synchronous high spatial resolution measurements of the 3 velocity components at the AIP. The effect of the passive flow control devices was investigated through multiple configurations with a systematic change of the design variables. The unsteady flow field was also numerically investigated with the Zonal Detached Eddy Simulation (ZDES) including passive flow control devices implemented with a Chimera grid. The use of vortex generators (VGs) within the S-duct changed the secondary flow, substantially restructured and stabilised the flow field at the AIP. As a result, the total pressure recovery could be improved with a reduction in pressure loss up to 30%. The steady total pressure distortion was also reduced with an improvement of up to 50% compared with the baseline configuration. The substantial influence of the VGs on the flow field unsteadiness typically reduced the unsteady swirl distortion by 67%. Consequently, extreme events that led to high swirl intensity for the baseline configuration were suppressed and the maximum swirl intensity was reduced by 45%. Similar findings were demonstrated for both S-duct geometries with a minor effect of the inlet Mach number on the swirl distortion. The results also highlighted the main coherent flow mechanisms that drives the unsteady distortion at the AIP with the occurrence of large deviations from the time averaged flow field for the baseline configuration. An extreme value theory methodology was established to estimate the maximum levels of peak total pressure distortion for these types of S-duct intakes based on reduced experimental data sets and to provide guidelines on its usage. The ZDES model was proven to be able to simulate the unsteady flow field at the AIP, to provide the time averaged and fluctuating levels of swirl distortion within 1% and 13% respectively of the measurements. The CFD solution was able to capture the main coherent structures and their characteristic frequencies as well as the rare and intense distortion events. The strong impact of the flow control devices on the AIP flow field was also captured by the ZDES. Compared with the measurements, the ZDES calculated similar levels of reduction of mean and unsteady swirl distortion as well as the correct pressure loss levels when flow control devices were used. Overall, this work quantified the highly beneficial impact of passive flow control devices on the unsteady total pressure and swirl flow fields for S-duct intakes. The use of S-PIV provided about 200 times more measurement points at the AIP than the conventional 40 high-bandwidth Pitot probes and demonstrated the necessity to assess the unsteady swirl distortion characteristics for the assessment of aero-engine intakes. Finally, the ZDES model was shown to be able to calculate the unsteady distortion with and without flow control devices which provides a viable method for industrial applications of aero-engine intake design at a reduced computational cost.en© Cranfield University, 2015. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.S-duct intakevortex generatorsunsteady flow distortionstereo-particle image velocimetryzonal detached eddy simulationextreme value theoryproper orthogonal decompositionThesis