High-Efficiency High-Resolution Characterization of Flow Velocity, Median Volume Diameter, and Liquid Water Content Uniformity in Simulated Icing Clouds

Aircraft icing is a potential threat to both commercial and military aviation. When aircraft encounter supercooled liquid droplets in the atmosphere, these droplets impact the aircraft fuselage, wings, and exposed engine components and freeze upon impact. Ice accretion can seriously affect the drag, lift, and control of the aircraft and, in serious cases, can cause fatal accidents to occur. To mitigate issues associated with aircraft icing, icing certification of aircraft engines are required. The present work will focus on the problem of engine icing and more specifically, characterizing icing test facilities to ensure that proper simulations are achieved for engine certification. The proposed project will result in the development of a system for characterizing the uniformity of flow velocity, median volume diameter (MVD), and liquid water content (LWC) in simulated icing clouds at the Arnold Engineering Development Complex (AEDC) free-jet engine test facility. This system will leverage light scattering interferometry and laser light sheet imaging techniques to assess uniformity. A compact, robust instrument based on the well-established phase Doppler interferometry (PDI) method will be mounted on a large-scale traverse system, enabling it to scan systematically across the flow field at the engine inlet plane. The PDI instrument provides highly accurate, high-resolution measurements of drop size and velocity for droplets ranging from 0.5 to 2000 µm in diameter and the air flow speed. This non-intrusive, reliable technique features a well-characterized sample volume, allowing for measurements of the droplet size distribution as well as population-level statistics and integral properties. PDI measurements of droplet velocity will be used to assess flow velocity uniformity. A specially designed large-scale traversing system will be fabricated and assembled to ensure comprehensive data collection across the entire flow field. Custom software will control the PDI instrument and traverse system, generating spatial uniformity maps of flow velocity, MVD, LWC, and other relevant variables. An innovative laser light sheet imaging technique will provide qualitative and quasi-quantitative evaluations of spray uniformity during engine tests. This method uses a laser light sheet to illuminate the flow field and high-resolution charge-coupled device (CCD) cameras will be used to capture images of the spray while the PDI instrument collects uniformity measurements. Subsequent image subtraction will be performed to further characterize spray uniformity during in situ engine testing. This integrated approach will result in a sophisticated system for efficiently and accurately measuring icing cloud uniformity at the AEDC free-jet engine test facility for aircraft icing certification testing. The PDI instrument will also provide a means for individual spray nozzle performance characterizations.