Recent Advances in Acoustics of Transitional Airfoils with Feedback-Loop Interactions: A Review

We discuss herein recent experimental and numerical studies examining resonant flow-acoustic feedback–loop interactions in transitional airfoils (i.e., possessing a notable area of laminar-to-turbulent boundary-layer transition) characteristic low-to-medium Reynolds number flow regimes. Such are commonly attributed to the viscous dynamics convected structures scattering into acoustic waves at trailing edge which propagate upstream re-excite vortical structures. While it has been long suspected that feedback mechanism is responsible for highly pronounced, often multi-tonal response, exact reason how instability could reach sufficient degree amplification sustain feedback-loop process exhibit specific tonal signature remained unclear. This review thus pays particular attention critical role separation bubble emphasizes complementary roles works elucidating an intricate connection between airfoil radiated properties zones as determined by geometry