Flow Parameters in Dominant Mode Selection of Self-Excited Oscillation in Slat Coves

This paper investigates self-excited oscillation within a slat cove and the flowfield parameters involved in selection of the main oscillation mode. Aeroacoustic experiments are described for aerodynamic noise characteristics on the leading-edge slat of a two-dimensional three-element high-lift configuration. Different geometrical settings are tested at varying angles of attack. A numerical simulation method is used as an auxiliary tool to analyze the flowfield. Based on previous research results and the experimental results obtained in this paper, a ratio of Lv/(delta .Kv) is proposed to evaluate the main mode of self-excited oscillation, where Lv is the shear-layer length within the slat cove, delta is the boundary-layer thickness near the point of separation, and Kv is the ratio of average vortex convection velocity along the shear layer to the maximum velocity in the shear layer near the cusp. The relationship between the aforementioned ratio and the main mode of oscillation is verified by far-field noise data for a high-lift configuration with different geometrical settings. As the slat translation along the chordwise direction of the main wing increases, the ratio Lv/(delta .Kv) also increases; and the main mode of self-excited oscillation switches from mode II to a transition phase, and then to mode III.