Utilizing a Laser Light Sheet Technique in a Boundary-Layer Flow to Study Different Transition Types

Abstract

A non-intrusive flow visualization technique for investigations in a boundary layer in air utilizing a laser-light sheet technique with adequate seeding is presented. The non-intrusive homogeneous seeding of the flow was realized by feeding the tracer particles into the flow with a seeding-rake located upstream of the grid and screens of the wind tunnel. We could also present a sophisticated excitation device which provided reproducible and constant initial conditions of the boundary-layer instabilities. Selecting different combinationsof the excitation signals, it was possible to investigate besides thefundamental and subharmonic transition the development of a single oblique wave and the oblique transition. This excitation together with the stated visualization technique enabled us to investigate effectively different transition types. Another important feature of this set-up is the phase-locked recording against the excitation signal facilitating the recording at a chosen phase with respect.