An Aeroacoustic investigation of an aerofoil equipped with a flexible trailing edge

The aeroacoustic characteristics of a symmetric NACA 0012 aerofoil with a flexible trailing edge are investigated in an anechoic wind tunnel. The chord-based Reynolds number is between 2.2×10⁵ and 1.2 × 10⁶. The aerofoil is at a zero angle of attack and the boundary layer is tripped near the leading edge. Flexible strips with different lengths and thicknesses are inserted into a slit along the span and extend out of the trailing edge of the aerofoil. Compared with the aerofoil without the flexible extension, the aerofoil with a flexible trailing edge can achieve a maximum noise reduction of 3.7 dB at a low free-stream velocity of 10–20 m/s , and the frequency of noise reduction is increasing with the free-stream velocity. Noise increase of 1–1.5 dB is also observed in the high-frequency region. Meanwhile, there appears a tonal noise for the cases of the long and thin flexible strips. The frequency of the tone is similar at different free-stream velocities, which is assumed to be due to the oscillation of the flexible strip at their own natural frequencies.