Reconstruction of a Disturbance Flow Field from Wall Measurements of Tollmien-Schlichting Waves

Abstract

In 2001, flight tests were performed in order to learn more about boundary layer transition induced by free-stream excited Tollmien-Schlichting waves. A sixty four element hot-film array, placed on the right hand wing of DLR’s flying test-bed LFU-205, was used to measure the wall shear stress fluctuations provoked by these instabilities while propagating in the laminar boundary layer. In the present work, a procedure was developed that allows the reconstruction of the disturbed flow field above the hot-film sensors from the wall measurements by employing linear stability analysis. The reconstruction delivers the fluctuations of all flow quantities, i.e. disturbance velocity components, pressure, temperature and density. A comparison of the reconstructed longitudinal disturbance velocity component $\mathrm{{u^\prime }}$ with hot-wire measurements shows good qualitative agreement.