Propeller slipstream effects on wing aerodynamics at low Reynolds numbers

Abstract

This dissertation investigates the effects of propeller slipstream on the aerodynamic performance of a downstream wing at low Reynolds numbers (70,000–130,000). The study addresses three objectives: quantifying aerodynamic loads under slipstream conditions, evaluating longitudinal riblets as a passive flow-control strategy, and comparing the effects of isotropic and propeller-induced turbulence on wing performance. Wind tunnel experiments were conducted using a two-bladed propeller and a NACA 0012 wing in a tractor configuration, with synchronized aerodynamic load and hot-wire measurements. The results show that propeller slipstream modifies both the steady-state and unsteady aerodynamic response of the wing. For the conventional midspan-aligned configuration, the slipstream increased lift and delayed stall, with larger gains at lower advance ratios; however, drag also increased, reducing (CL/CD)max relative to the isolated wing. The unsteady response exhibited a U-shaped variation with advance ratio, with lift fluctuations decreasing at intermediate values and increasing toward both lower and higher advance ratios, primarily due to the phase-locked component. Propeller placement and rotation direction also influenced aerodynamic performance. A wingtip-aligned propeller with inboard-up rotation reduced drag and achieved the highest aerodynamic efficiency but produced larger unsteady lift fluctuations at higher advance ratios. Longitudinal riblets reduced drag and suppressed phase-locked boundary-layer velocity fluctuations but did not reduce the integrated unsteady loading on the wing. Comparisons between grid-generated turbulence and propeller slipstream at nominally matched conditions further showed that turbulence intensity alone is insufficient to represent propeller slipstream inflow, as the slipstream cases exhibited different stall characteristics, larger unsteady lift fluctuations, and discrete spectral peaks at the blade passage frequency.