Experimental investigation of unsteady fan-intake interactions using time-resolved stereoscopic particle image velocimetry

• Achieved unsteady, coupled intake-fan measurements with particle image velocimetry. • Advanced characterization of flow distortion approaching rotor fan blades. • Fan rotor increased swirl intensity at blade tips and influenced flow distribution. • Swirl angle unsteadiness reduced across key flow distortion frequencies. • Methods can influence industrial testing for future aircraft engine certification. Understanding engine response to unsteady intake flow distortion is a crucial requirement to de-risk the development of novel aircraft configurations. This is more critical for configurations with highly embedded engines. Recent advances in non-intrusive, laser-based flow diagnostics demonstrated the ability to measure unsteady flows in convoluted intakes with high resolution in time and space. This work presents novel non-intrusive, unsteady flow measurements ahead of a fan rotor coupled to a convoluted diffusive intake. The fan rotor caused a local increase of the maximum levels of swirl intensity at the blade tip region, as well as flow re-distribution at the interface plane between the fan and the inlet duct compared to the baseline configuration with no fan in place. This contributed to the reduction of the overall swirl angle unsteadiness across the main flow distortion frequencies. This research presents a notable advance in unsteady fan-intake interaction characterisation. The work shows that high-resolution optical measurements offer notably better understanding of these complex aerodynamic interactions and have the potential to be part of larger scale, industrial testing programmes for future product development and certification.