Unsteady swirl distortion characterization in a coupled fan-intake system in crosswind conditions using stereoscopic particle image velocimetry

Abstract

Swirl distortion is one of the key factors influencing the aerodynamic performance of coupled intake–fan systems. This study presents a detailed analysis of Stereoscopic Particle Image Velocimetry (S-PIV) data acquired on a circular plane within an aero-engine intake operating under crosswind conditions, including a ground plane and a co-rotating ground vortex ingested ahead of a rotating fan. Two flow conditions were examined: one exhibiting diffusion-driven separation at low fan speed and Mass Flow Capture Ratio (MFCR), and another with attached flow at higher fan speed and MFCR, both at constant crosswind velocity. This work demonstrates the effective implementation of PIV measurement techniques to a coupled fan–intake system in an industrial setting, achieving unprecedented flow-field resolution and data fidelity. Swirl distortion descriptors obtained from experimental data are used to produce Extreme Value Theory (EVT)-based forecasts of peak swirl intensity, which is the novelty of the work. Key contribution includes the identification of notably different swirl distortion characteristics between attached and separated intake flow conditions. Fan-face swirl distortion was found to be significantly more severe in the separated case, with time-averaged and peak swirl intensities up to three and four times higher, respectively, than in the attached case. The analysis at a radial position near the fan tip showed that peak swirl distortion can differ substantially from global, area-averaged metrics. These high distortion levels, particularly near the fan tip, indicate a potentially significant reduction in rotor incidence angle and, consequently, a loss in fan performance. The impact of this work is the establishment of an experimental and analytical framework that advances the understanding and quantification of swirl distortion in coupled fan-intake systems, offering a basis for improved industry standards, shorter testing durations, and more accurate prediction of extreme distortion levels.