Vortex Shedding and Noise Radiation from a Slat Trailing Edge

摘要

Vortex shedding and the associated noise radiation from a trailing edge were experimentally investigated for anleading-edge slat of amulti-element airfoil at stowed chord Reynolds number < 5:9 u0001 105n. A particular focus wasnon the competition between the instability of the slat boundary layer excited by acoustic feedback and the absoluteninstability of the wake. Periodic vortex shedding was observed to occur from the slat trailing edge at the Reynoldsnnumbers examined. For < 1:9 u0001 105n, the vortex shedding is governed by the absolute instability of the laminarnwake of the slat without any distinct tonal noise radiation. For > 2:1 u0001 105n, however, acoustic feedback becomesnpronounced between the trailing-edge noise and the boundary-layer instability waves on the suction surface, so thatnmultiple spectral peaks appear both in the velocity fluctuations and sound pressure. At and around the Reynoldsnnumber for the first appearance of tonal noise, u0002 1:9 u0001 105n, both of the instability modes coexist. Beyondnu0002 2:1 u0001 105n, the boundary-layer instability waves excited by the acoustic feedback evolve into high-intensitynvortices before reaching the trailing edge and suppress the absolute instability of the wake through diminishing thenreversed-flow region in the wake.