Review of slat noise mechanism and control in high-lift devices

During aircraft landing, the slat of high-lift devices is an important source of airframe aerodynamic noise. In recent decades, a large number of wind tunnel tests on slat noise have been carried out domestically and abroad. A deep understanding has been achieved on the characteristics and mechanisms of slat noise, and many attempts have been made in flow control and noise reduction technologies. Slat noise mainly includes low-frequency broadband noise, low-frequency discrete tonal noise, and high-frequency tonal noise. In this paper, the main research progress of wind tunnel testing on two-dimensional airfoil slat noise is reviewed and analyzed, and the generation mechanisms of the three slat noise components are introduced in detail. There are three main categories of control methods for slat noise. The first is the fairing method represented by the slat cove filler, which removes or limits the generation of recirculation flow and hence significantly reduces noise. The second is applied at the slat cusp to interfere with the formation of coherent structures in the shear layer. From the perspective of engineering feasibility, the third category is to optimize the slat slot and structural parameters or to adopt new configurations with leading edge droop as an example. In summary, in order to achieve efficient noise control technologies, it is necessary to deeply understand the complex phenomena in the shear layer flow of the slat cove, such as the fluid-acoustic coupling and its interference with the slat trailing edge, through advanced testing methods and experimental schemes.