Slat aerodynamics and aeroacoustics with flow control

Abstract

This study primarily investigated the flow and aeroacoustics associated with the slat of a three-element aerofoil in approach conditions. The study assessed importance of several factors and examined their aerodynamic impacts. The factors investigated were aerofoil incidence, slat angle, slat cusp geometry, fixing transition and blowing in the slat cove. A combination of experimental and computational techniques investigated the factors selected. The experimental work employed PIV, pressure tap, a force balance, flush mounted microphones and an acoustic array. The computational work used DES along with the FW-H acoustic analogy to obtain the far-field directivity. Tonal features occurred at high incidence and originated at the slat trailing edge, due to the blunt trailing edge and gap, and at the reattachment point. Fixing transition removes the tone at the reattachment point and reduces the slat gap tone at the trailing edge but does not remove the tone generated by the blunt trailing edge. All of the tones found, only occurred at certain slat and wing settings. Broadband sound was present in all conditions but had a strong dependence on the incidence of the wing. The sound was loudest with the wing at ? = 5o with a reduction as the wing incidence was increased. The broadband sound also reduced as the slat angel decreased from ?S = 23o. The shear incidence angle was a good indicator of the impact of these two factors on the sound generated. Extending the slat cusp reduced the broadband sound at low aerofoil incidence. However, for ? ? 10o the extension led to increased broadband sound. Neither blowing nor fixing transition had a significant impact on the broadband sound generated by the slat system. The aerodynamic loads generated by the wing were mainly dependent on the aerofoil incidence. However, other factors did influence the forces generated. Reducing the slat angle increased the lift generated by the wing especially at low aerofoil incidence but the lift to drag ratio was unaltered. At high aerofoil incidence, extending the slat cusp reduced the lift generated. Blowing and fixing transition did not significantly alter the forces generated by the wing.

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