Research on coherence of unsteady flow of multi-element airfoil

The unsteadiness of the flow around the three-element airfoil under various conditions are investigated by dynamic pressure sensor in the NF-3 Low speed wind tunnel in Northwestern Polytechnical University, which focus concentrates mainly on the coherence of surface unsteady pressure. The effect of the Reynolds number, angle of attack and the parameters of the trailing edge flap, such as angle of flap, slot width, overlapping amount, on the surface unsteady pressure of the unsteady flow are analyzed. Results show that the coherence curve of the surface point unsteady pressure on the each section of the three-element airfoil is much the same and has nothing to do with the wind speed, when the abscissa is the Strouhal number r S ; the degree of coherence of the surface point unsteady pressure is relatively high when r S range from 0 to 10; the surface point unsteady pressures show a strong coherence at the same frequency range at leading edge and cove of and behind the trailing edge of slat, which shows the unsteadiness of the surface point unsteady pressure are related to vortex generation and shedding on the slat; the unsteadiness of the slat flow strengthen and the coherence of the surface point unsteady flow of slat also increases when the angle of attack or the flap deflection angle increase.