Pressure Wave Damping Effects of Trailing-Edge Brushes on a Supercritical Airfoil

Despite extensive research in the field of transonic wing flow, the origin of self-sustained unsteady phenomena such as shock buffet remains a topic of significant theoretical and practical interest. Associated aerodynamics and the resulting wake are major contributors to load oscillations and aircraft noise, which have long been a focus of mitigation efforts. Contrary to most related experimental research, this study focuses on the flow behavior near the airfoil surface rather than the resulting wake. This is done to determine the effect of trailing-edge brushes made from small polyamide fibers on buffet behavior and to characterize a related influence on aerodynamic loads and airfoil noise. Experiments are performed on a BAC3-11 airfoil for subcritical, critical, and supercritical flow conditions ([Formula: see text], 0.72, and 0.74) with systematic variation of the fiber diameter and length. The chord-based Reynolds number is kept constant at a value of [Formula: see text]. High-resolution surface pressure measurements and high-speed schlieren images are used to examine the change in flow dynamics as compared to the unmodified airfoil. The spectral amplitudes and signal energies of occurring pressure waves for both cases are derived with dedicated Fourier analyses and compared to reveal damping of wave intensities for a wide range of tested brushes. The strongest damping effect occurs when brush eigenfrequencies align with dominant flow-induced wave frequencies, indicating frequency-tuned passive control as a promising strategy for aeroacoustic mitigation.