上流境界層内に設置した噴流の設置間隔がキャビティ音に及ぼす影響

Abstract

This work presents an experimental investigation for effects of the spanwise spacing of small-jets placed in the approaching boundary layer on cavity tone. The sound and velocity fields of a flow around a cavity were measured with a low noise wind tunnel. The freestream velocity was changed from U0 = 10 - 45 m/s. The depth-to-length ratio of the cavity was D/L = 0.5. The upstream boundary layer is laminar, and the boundary layer thickness is δ/L = 0.065 at U0 = 30 m/s. The effects of the jets from the wall in the upstream boundary layer with various spanwise spacing p/L = 0.1, 0.25, 0.4, 0.5, 0.6 and 1.0 on the cavity tone were investigated. The jet velocity was Uj = 3.0 m/s. The results show the cavity tone can be reduced by control of blowing jets. The control effect on the cavity tone depends on the spanwise spacing and velocity of blowing jets. In this experiment, the most effective spanwise spacing of jets for noise reduction was p/L = 0.4 - 0.6. The three-dimensional spanwise velocity field was induced by blowing jets. As a result, the spanwise coherence of the vortices inducing intense sound became weak, and the radiating sound became weak.