Effects of bulb seal on slat flow dynamics and slat tones

The Delayed Detached Eddy Simulation (DDES) and Ffowcs Williams–Hawkings (FW–H) analogy have been performed to describe the unsteady flow and noise-generation process involved in slat flow analysis for the 30P-30N multi-element wing, as well as to predict the discrete tone frequencies based on the Rossiter's formula. And combining the discrete tonal frequencies distribution and previously summarized bulb seal installation location, a method for installing the bulb seal on the slat cusp for noise reduction study is proposed. And finally, the noise reduction mechanism of the bulb model has been revealed by Proper Orthogonal Decomposition (POD) and Cross-correlation methods. The result shows that the bulb seal changes the distribution of flow dynamics and pressure fluctuations, thus effectively reducing the first mode energy by about 13% and the far-field noise by approximately 3 dB. The bulb seal accelerates flow separation to form a turbulent shear layer, weakening the Kelvin–Helmholtz (K–H) instabilities, delaying the formation of large-scale vortex structures and vortex–vortex interference and merging, effectively reducing the discrete tone peaks and the flow correlation around the slat cove, so that a portion of the noise source in the slat gap vanishes and the local noise source moves towards the leading edge of the main wing.