We address our long-standing claim that vortex reconnection is one of the dominant sources of aeroacoustic noise in a number of canonical turbulent flows. The reconnection of two antiparallel vortices is studied via direct numerical simulation of the compressible Navier-Stokes equations in order to fully resolve the acoustic noise generation and far-field sound wave propagation. We show that the primary acoustic source is initially located at the contact point and then at the bridges, where reconnected vortex lines accumulate. At the start of reconnection, the sharp near-field pressure rise results in a high level of far-field noise with a clear dipole pattern. As more vortex lines reconnect and recoil from each other by self-induction, the near-field low-pressure zone extends in both the axial and lateral directions, which results in a quadrupole far-field noise. We thus reveal and quantify sound pressure levels and directivity during vortex reconnection. This work paves the way for further investigations of the reconnection generated noise, especially at higher Reynolds numbers.

中文翻译：

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涡流重新连接导致产生航空声噪声

我们提出了一个长期存在的主张，即涡旋重连是许多规范湍流中主要的气动声源之一。通过可压缩的Navier-Stokes方程的直接数值模拟研究了两个反平行涡旋的重新连接，以便完全解决声噪声的产生和远场声波的传播。我们表明，主要的声源最初位于接触点，然后位于桥处，在这里重新连接的涡流线会累积。在重新连接开始时，急剧的近场压力升高会导致高水平的远场噪声，并具有清晰的偶极子模式。随着越来越多的涡流线通过自感应彼此重新连接并反冲，近场低压区在轴向和横向都延伸，产生四极远场噪声。因此，我们揭示并量化了涡旋重新连接过程中的声压水平和方向性。这项工作为进一步研究重新连接产生的噪声铺平了道路，尤其是在雷诺数更高的情况下。