EXPERIMENTAL STUDY OF HUMIDITY-DRIVEN PARTICULATE FOULING ON ENGINEERED SURFACES IN ULTRA-HIGH BYPASS RATIO AIRCRAFT ENGINES

Abstract

Engine heat transfer surfaces in ultra-high bypass ratio (UHBR) turbofan engines are exposed to particle-laden high speed flows in a humid environment that causes particulate deposition and progressive degradation of thermal performance. Therefore, an experimental test facility is developed to study the influences of surface topology, flow velocity, and humidity on particle transport and deposition mechanisms in humidified bypass flow conditions. The experimental test are performed with Arizona Road Dust and the flow velocities can be set between 90 m/s and 230 m/s under controlled thermodynamic conditions and relative humidity levels ranging from approximately 30% to 100%. The particle deposition and surface degradation is quantified using full-field optical profilometry, enabling spatially resolved measurements of the deposit thickness and roughness evolution. The experiments show that no measurable particle deposition is observed at low humidity (30% RH), indicating that dry adhesion forces are insufficient to overcome wall shear stresses at these velocities. In contrast, saturated conditions (100% RH) resulted in stable deposit formation, with particles preferentially accumulating in low-shear recirculation regions on the upstream side of the dimple cavities. Increasing the jet velocity from 96.5 to 116.8 m/s reduced the deposited mass by nearly one order of magnitude, demonstrating the dominant role of shear-driven removal. The experimentally observed deposition patterns suggest a correlation with the CFD predicted wall shear stress distribution. Furthermore, it is observed that the surface roughness of the test specimen is altered throughout the deposition experiments.