Effect of an excrescence in the slat cove: Flow-field, acoustic radiation and coherent structures

Slat noise during aircraft landing is already a barrier to the development of quieter commercial airplanes. Investigations have been made by several research groups to understand the mechanism of slat noise generation. Most of the published works related to slat noise consider clean idealized geometries, whereas real slats contain some imperfections to enable its operation. The influence of a protrusion on the slat cavity surface on the unsteady flow around the slat and on the propagated sound was here investigated via numerical simulations. The protrusion models a sealing device designed to avoid metal–metal contact. A commercial code based on the Lattice-Boltzmann method was used to compute the unsteady flow. The far-field acoustic propagation was calculated by means of the Ffowcs Williams–Hawkings analogy and the Proper Orthogonal Decomposition (POD) was used to investigate the dynamics of the cove flow. The effect of the seal on the time-averaged pressure distribution is limited to the region close to it. However, tonal peaks in the noise radiated from the slat region are significantly higher when the seal is introduced. The present results show that, at the frequency of one of the tonal peaks, pressure fluctuations outside the cove are highly correlated with large-scale structures in the cove mixing-layer and at its impingement on the slat lower surface. The results also show that the introduction of the seal increases the coherence of these structures.