Pulsed-Sound Measurements of the Influence of High-Amplitude Noise on Boundary-Layer Transition to Turbulence

摘要

An experimental study of leading-edge receptivity to high-amplitude acoustic forcing was conducted in the low- turbulence Arizona State University Unsteady Wind Tunnel. The experiment examined unstable wave evolution in a Blasius boundary layer produced on a flat plate. A pulsed-sound technique was employed to generate Measurements of receptivity coefficients for a 20:1 modified-super-ellipse leading edge. The leading-edge profile ensures that there is no curvature discontinuity at the flat-plate juncture, therefore limiting the receptivity sources. The goal of the pulsed-sound method was to prevent the superposition of the Stokes and Tollmien-Schlichting (T-S) waves that were prevalent in previous experiments. Separation was achieved via a short acoustic pulse, followed by the conditional sampling of the boundary layer. The resulting signal yielded a pure T-S wave. The signals were examined in the frequency domain, where the magnitudes of the ensemble-averaged Fourier coefficients were used to calculate the receptivity coefficients. These experiments resolved the erroneous narrow pass-band response of all other experiments, extended the measurement range of previous experiments, and provided very good validation of analytical and numerical models. Results revealed good agreement with linear stability theory. Receptivity coefficients are presented and the first step to a transition prediction scheme has been completed.