MEASUREMENTS OF T-S WAVES DUE TO ACOUSTIC DISTURBANCES IN EXPERIMENTS

Boundary-layer receptivity to external disturbances plays a key role in transition from laminar to turbulent flow. However, studying the process of how disturbances become entrained in the boundary layer remains challenging, especially in experiments. As a common external disturbance, the acoustic disturbance interacts with the localized roughness to create Tollmien-Schlichting (T-S) waves in the boundary layer. Measurements of T-S waves under this situation is complicated mainly by the presence of the Stokes wave which has the same frequency with the former. This study isolated the T-S waves from the Stokes waves in two varied ways under both continuous and pulsed acoustic disturbances and compare their results with the linear stability theory (LST). The receptivity to acoustic disturbances with different thickness of the 2-D roughness was also evaluated quantitatively, which is consistent with other numerical results.