Impact of Propeller Tip Vortices on Turbulent Boundary Layers

Hybrid electric propulsion systems featuring Over-The-Wing (OTW) propellers offer substantial advantages, providing an increased lift-to-drug ratio. A critical issue arises from the intricate interaction between tip vortices and the turbulent boundary layer, leading potentially to flow separation. Understanding the dynamics of the intricate interactions between tip vortices and the boundary layer and the underlying causes of flow separation is crucial. To address these challenges, an experimental investigation using a 3 cameras planar Particle Image Velocimetry (PIV) system was conducted. The study focused on the propeller wake structure's effects on the turbulent boundary layer at high Reynolds numbers. The experimental analysis evaluated the propeller's impact on boundary layer development, encompassing flow statistics, as well as coherent and vortical structures. By comparing two different tip clearances, the influence of the propeller's distance from the wall on the boundary layer was assessed. Through a phase-locked and conditional analysis of vorticity and turbulent energy production mechanisms, the major sources of viscous losses were identified. The effects of periodic vortical structures, random fluctuations and non-linear interactions are separately analysed. The knowledge gained can contribute to the design and optimization of future propulsion systems for improved efficiency and performance, addressing the challenges associated with OTW propellers and advancing hybrid electric propulsion technology.