Slat Noise Suppression with Mass Injection

The efficiency and mechanism of slat noise suppression with upstream mass injection was investigated through validated numerical simulations. Delayed detached-eddy simulation was used to describe the noise sources and Ffowcs Williams-Hawkings integration was carried out to obtain the far-field noise characteristics. Outward mass injection from the suction side of the slat near the cusp uplifted the free shear layer, and the corresponding impingement of free shear layer with slat pressure surface was alleviated. The tonal component of the far-field noise was diminished, and the suppression of the broadband noise was also observed. The inward injection of mass at the pressure side of the slat near the cusp facilitated the three-dimensional flow and the breakup of large-scale spanwise vortices, weakening the strength of the free shear layer, especially at the vicinity of the reattachment point. However, the introduction of strong turbulence at the downstream of the injection slot offset the benefits gained from the suppression of unsteadiness at the reattachment area. Although the low-frequency sound pressure level was lowered, two new strong peaks arose at higher frequencies, which contributed to a higher overall sound pressure level at the upstream direction below the airfoil.