In-flight and wind tunnel measurements of natural and of controlled instabilities on a laminar flow airfoil

Abstract

The temporal and spatial development of natural Tollmien-Schlichting (TS) instabilities and artificially generated disturbances was investigated comprehensively in-flight as well as in a wind tunnel. The experiments were performed on a laminar wing glove for a sailplane using different surface sensor arrays (surface hot-wire sensors, piezo-sensor arrays). Two-dimensional TS waves dominate in the early linear stage of the boundary layer flow, but single three-dimensionally (3D) dominated wave packets, observed in the late stage of TS development, can be measured in the early stage as well. Furthermore, in the in-flight measurements, the 3D-instabilities occur earlier than in the wind tunnel. For the experiments on controlled transition, an array of spanwise distributed harmonic point sources which induced mono and multifrequency disturbances was used in order to compare the development of natural and controlled instabilities. © 2006 Springer.