Propagation of Tollmien Schlichting waves in a wing boundary layer

So far, very little is known about instability wave propagation in a wing boundary layer in free flight. Therefore, flight tests were performed in order to investigate under conditions of natural excitement Tollmien-Schlichting waves as primary instabilities in transition to turbulence. Measurements were done with a 64 element hot-film array. the array was bonded to a laminar glove on the right hand wing of the flying testbed LFU 205. Amplitudes of wall shear stress fluctuations induced by Tollmien-Schlichting waves were quantified by employing a calibration procedure for hot-film sensors. Analysis of measured data reveals a brodband frequency spectrum of TS-instabilities typical for wave packages, while the spanwise extend of wave trains is comparatively small (in the order of about 3 wavelengths)