LAUSR

Regarding the flow noise interference mechanism of tandem shallow cavities, experimental research on the near-field flow field characteristics and far-field acoustic field characteristics of two cavities of the same size along the flow direction in tandem was carried out. The incoming flow velocity was adjusted from 60 to 80 m/s at the intervals of 5 m/s, which corresponded to Reynolds numbers from 6.6 × 105 to 8.8 × 105. A spacing distance between the tandem cavities is from 0.25 to 4 times the cavity length. The experimental results show that the variations of all the fluctuation characteristics basically occur below 500 Hz, both for the near-field wall pressure and for the far-field acoustic pressure. When the spacing distance is small, the near-field flow characteristics of the upstream cavity change very little, but the low-frequency broadband pressure fluctuation of the downstream cavity is excited; when the spacing distance is large, the low-order flow–acoustic feedback modes of the upstream cavity are excited, and the intensity of pressure fluctuation in the corresponding characteristic frequency as well as the nearby frequency bands increase significantly, while the intensity of pressure fluctuation in the downstream cavity decreases slightly. This leads to a significant increase in the far-field noise of the tandem cavities below 500 Hz, and the increase is larger in the upstream of the tandem-cavity system than in the downstream.