Evaluation of initial amplitudes of free-stream excited tollmien-schlichting waves from flight-test data

Abstract

Flight tests were performed in order to learn more about free-stream excited Tollmien-Schlichting waves and the role they play in boundary layer transition. Therefore, a multi-element hot-film array, placed on the right hand wing of the flying testbed LFU-205, was used to sense the skin friction fluctuations provoked by this type of instability while propagating in the laminar boundary layer. The experimental data acquired were subsequently analyzed with special emphasis on the evaluation of the initial amplitudes of Tollmien-Schlichting waves. For the streamwise disturbance velocity component their magnitude was determined to be in the order of 10-9 times the boundary layer edge velocity. © 2007 Springer-Verlag Berlin Heidelberg.