Experimental investigation of the effects of propeller-wing interaction on wing aerodynamics at low reynolds number flows

The effects of PWI on aerodynamic performance were experimentally investigated in the low Re regime (Re < 500,000), typical of UAV, MAV, and UAM platforms. The fundamental challenge encountered in this flow regime is the formation of the LSB, which deteriorates wing performance and induces unsteady flow conditions. Focusing on complex mechanisms such as wingtip vortices, PWI, LSB, and ground effect, utilized the NACA 4415 airfoil and a tractor-type propeller configuration commonly employed in low-Reynolds air vehicles. A finite wing with (AR: 3.8) was tested in a wind tunnel across varying Re, 𝛼, advance ratios, propeller positions, and propeller configurations. Experimental data were acquired via force measurements using a load cell and surface oil flow visualization techniques. Distinct from existing studies in the literature, this thesis systematically analyzes aerodynamic coefficients not solely as a function of the J, but by isolating parameters such as different propellers at constant RPM, varying diameter at constant pitch, and varying pitch at constant diameter. Additionally, the unsteady effects of the propeller slipstream on the wing were examined using data from the load cell. Results show that the slipstream energizes the boundary layer, delaying flow separation and locally suppressing LSB formation. Particularly at low J, increases of up to 100% in 𝑚𝑎𝑥imum lift coefficient were recorded compared to the clean wing configuration, and the stall angle was delayed by 2°. Concurrently, it was observed that increasing the propeller diameter plays a more dominant role in augmenting lift coefficient compared to increasing the pitch; however, this also results in an increase in total drag coefficient due to induced drag. Unsteady analyses of the propeller-wing configuration revealed significant fluctuations in wing loading. Consequently, to balance the takeoff/landing (high lift coefficient) and cruise (low drag coefficient) performance requirements of platforms such as MAVs, a hybrid propeller selection and placement strategy is proposed. This strategy integrates large-diameter propellers, which provide high thrust at low J, with optimum pitch values that maintain cruise efficiency.