Boundary Layers Explained: An Undergraduate Laboratory Using an Aerofoil with Leading-Edge Slat

Abstract

A new undergraduate laboratory exercise is described which explores the generation of lift over an aerofoil with and without a leading-edge slat. The experiment emphasises a fundamental understanding of the fluid-dynamic boundary layer and supports a second-year lecture course in fluid mechanics. A NACA 2415 aerofoil is used by the undergraduates in a simple open-return circuit wind tunnel at a Reynolds number of 2 × 105. Measurements of inviscid and viscous aerodynamic characteristics of the aerofoil are validated against cambered aerofoil theory and published NACA data. Oil surface-shear flow visualisation and the differences in the pressure distribution around the NACA 2415 with and without the leading-edge slat demonstrate the governing influence of the boundary layer on aerodynamic stall and the lift generated by the aerofoil. The new laboratory format was introduced to the undergraduates in 2007 and the response from student evaluation questionnaires confirmed that their understanding of basic fluid dynamics was greatly enhanced by the wind tunnel experiment.