Investigation on intensity of tones due to self-excited oscillation within the leading-edge slat cove at different incoming flow speeds

To provide further understanding of the low to mid frequency tonal noise characteristics of the leading-edge slat in the processes of take-off and landing, both experimental and numerical investigations are carried out on a two-dimensional high-lift configuration, with a stowed flap at varying incoming flow speeds (from 30 m/s to 60 m/s). The intensity variation of the low to mid frequency tonal noise is found to be closely related to the selection of the main mode of self-excited oscillation within the leading-edge slat cove. With increasing incoming flow speed, the main mode of the self-excited oscillation switches to a higher one. Meanwhile, the ratio of the self-excited oscillation period to the vortex shedding period is introduced to explain further the relationship between the main mode and incoming flow speed. As the incoming flow speed increases from 30 m/s to 60 m/s, the self-excited oscillation period is basically constant due to the flow similarity, whereas, the vortex shedding frequency is gradually increasing. The characteristic frequency of the shedding vortex near the cusp is found to be approximately proportional to 3/2 of the incoming flow speed power law.