Suppression effect of the leading-edge groove on deep cavity noise at low speeds: Groove length

Abstract

Detached Eddy Simulations combined with Ffowcs Williams–Hawkings acoustic analogy of subsonic flows over a deep cavity preceded by deep grooves with different lengths were conducted to investigate the effects of groove length on the flow characteristics and the noise suppression in the vicinity of the deep cavity. The length-to-depth ratio of the deep cavity is 2/3, and the length-to-depth ratios of the grooves are 1/2. The distance between the grooves and the cavity remains constant at twice the groove length. The groove length ranges from 5 mm to 30 mm. The Reynolds number based on the cavity length is 8 × 10−5. The analysis results indicate that all grooves studied in this paper have some effect on the distribution of sound energy of near-field noise and near-/far-field noise amplitude, but have no effect on the characteristic frequencies of cavity noise and far-field noise directivity. When the groove length is 15 mm and 20 mm, the deep grooves are most effective in suppressing deep cavity noise. The time-averaged velocities in the incoming boundary layer, shear layer, and wake region decrease, and the height of the boundary layer downstream of the cavity increases, which reduces the intensity of the interaction between the flow structure and solid wall downstream of the cavity, resulting in a reduction in flow-acoustic feedback noise. Meanwhile, the suppression effect of the groove flow on the cavity flow effectively alters the flow characteristics of the entire cavity mouth, the rear edge wall, and part of the bottom surface region, reducing the energy at these locations. This is the primary reason for the reduction in broadband noise and acoustic resonance noise.