Abstract:
In this paper, the experimental study of stall control of a straight wing by bio-inspired flexible serrated coverts was conducted in the subsonic close-loop low-turbulence wind tunnel in Tianjin University. The NACA0018 wing model had a chord of 300 mm and a span of 1.0 m, and it was installed at the angle of attack of 15°, resulting in a stalling flow phenomenon in the wake. The chord-based Reynolds number was
Re = 5.1×10
5. The spanwise coverts were fixed at multiple positions on the upper surface, and the resulting wake flow velocity was measured with the hot-wire anemometer. The averaged velocity, fluctuating velocity and power spectral density etc. were compared between the cases with and without control. Experimental results show that the coverts at the 20% chord adaptively flap with the flow, whereas the coverts at the 80% chord slightly flutter at a quasi-equilibrium position. The averaged velocity loss in the wake zone is recovered obviously in the two conditions, and the turbulent fluctuation in the shear layers of both the leading and trailing edges decreases obviously. The control effect on the stalling flow is realized under both conditions. Moreover, the power spectral densities and discrete wavelet analyses reveal that the adaptive coverts suppress the low/medium-frequency large-scale flow structures (
fc/
U∞<1), and convert them into high-frequency small-scale ones (
fc/
U∞≈3), leading to higher spectral coherence between the leading edge and trailing edge shear layers. The mechanism of bird coverts in stalling flow control at high angle of attack of a straight wing is thus revealed.