Passive control of aerodynamic noise past a transonic cavity

Accurate prediction and control of flow-induced noise from cavities on aircraft surfaces have long been challenging and hot research topics in aeroacoustics. This study focuses on the aerodynamic noise induced by near-field pressure fluctuations over the M219 cavity benchmark model and its noise reduction control. The Improved Delayed Detached-Eddy Simulation (IDDES) method is employed to compute the separated flow structures around the cavity, and the Spectral Proper Orthogonal Decomposition (SPOD) method is utilized to deeply investigate the correlation between flow modes and noise characteristics. Passive flow control using wire mesh is implemented, and the underlying mechanisms of noise reduction effects influenced by different mesh heights and porosities are revealed. Analysis indicates that while part of the flow passes through the wire mesh, another part is obstructed and lifted. This unique flow-dividing mechanism consequently suppresses the vortex-sound feedback loop within the cavity, resulting in a significant reduction of aeroacoustic noise through alterations in the flow structure. When the wire mesh height is small, no noise reduction effect is observed. However, when the mesh height reaches 3 cm, the average noise reduction at the cavity floor reaches 5.61 dB, and significantly superior to that of a solid rectangular baffle. Wire meshes with porosities of 0.3 and 0.64 vary in their suppression effects on the vortex-sound positive feedback loop, while both demonstrate superior noise reduction performance compared to the solid rectangular baffle.