In-Flight and Wind Tunnel Investigations of Natural Transition on a Laminar Flow Airfoil

Abstract

The temporal and spatial development of natural Tollmien-Schlichting (TS) instabilities in the linear and weakly nonlinear stage were investigated in extensive flight as well as in wind tunnel experiments on a laminar airfoil. Two-dimensional TS waves dominate in the early linear stage of the boundary layer flow, but small three-dimensional disturbances are already existent. These individual and spatial independent wave packets are amplified later than the two-dimensional waves and they dominate the late stage of the TS development. The experiments were carried out on a laminar profile performed as a glove for a sailplane, employing different surface sensor arrays (surface hot-wire sensors, piezo sensors, microphones).