Physics of Acoustic Excitation on Boundary Layer Development
V. Sokolenko, W. Elsner, A. Dróżdż, R. Gnatowska
Częstochowa University of Technology, 42-201 Częstochowa, Poland
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In such a complex system as a modern turbofan engine, the laminar boundary layers developing on surfaces of turbine blades are exposed to strong perturbations caused by acoustic waves. A high concentration of acoustic energy inside such an engine, apart from other negative aspects such as fatigue loadings, can also have a major impact on the stability of the laminar boundary layer and can trigger an earlier laminar-turbulent transition. This work examines the effect of acoustic excitation at broadband frequency range on a boundary layer developing on a flat plate subjected to a weak adverse pressure gradient. The experiment was conducted with a low inlet turbulence intensity level (Tu>1%) to provide a cleaner environment that magnifies the effects of the excitation frequency. It was shown that acoustic excitation can lead to a more rapid increase in flow instability followed by an earlier l-t transition. The paper also demonstrates that broadband acoustic excitation modifies the physics of the near-wall flows by amplifying the frequency which is the 2nd harmonic of two-dimensional Tollmien-Schlichting (T-S) waves.

DOI:10.12693/APhysPolA.139.613
topics: boundary layer physics, acoustic waves, flow control, receptivity