Unsteady Surface Pressure Measurements on a Laminar Wing submerged in a Propeller Slipstream

Abstract High-frequency surface pressure measurements on a Natural Laminar Flow (NLF) airfoil submerged in the wake of a propeller were conducted in the Laminar Wind Tunnel (LWT) of the Institute of Aerodynamics and Gas Dynamics (IAG) of the University of Stuttgart. Based on the measured unsteady pressure signals, the laminar-to-turbulent transition on the airfoil is investigated. The resulting data can be used to further understand the interactions between a tractor-propeller and the boundary-layer (BL) flow. By gaining insights into BL-flow behaviour under such conditions, more efficient airplane propulsion and wing designs could become viable. With the aid of high-frequency pressure sensors, it is possible to create a 2-dimensional resolution of the boundary layer state, along the spanwise position behind the traversable propeller and the chord of the airfoil. At certain advance ratios, laminar regimes are recorded reaching up to x/c = 80 %, far beyond the steady chord transition location of the NLF configuration. Depending on the advance ratio, the mean portion of laminar flow still varies in between 35 − 44 %, corresponding to 63 − 81 % of the NLF distance of the steady reference configurations without a propeller installed. This clearly demonstrates the importance of considering the partly laminar boundary-layer flow behaviour on the airfoil, even when submerged in a propeller wake.