Dynamics and Statistics of Worms around a Calumnar Vortex

用数值方法研究了柱状涡与外部湍流的相互作用。Lamb-Oseen涡浸入初始各向同性均匀湍流中，其本身是通过直接数值模拟衰减湍流产生的。通过流场的可视化，详细研究了柱状涡周围非均匀细涡流的形成和涡核变形。最初随机的湍流漩涡（蠕虫）被包裹在柱状涡旋周围，变成旋涡环（或螺旋）。统计量，如两点能谱和两点熵谱，通过平均20个实现来评估，并与快速失真理论（RDT）的理论预测进行比较。在涡旋表面附近，轴向速度相关性占主导地位，而在涡旋被包裹的地方，径向速度相关性变得更大。如果柱状涡较外部湍流强，则外部速度扰动被涡阻挡，不能直接穿透涡核，而各种类型的涡波（开尔文波）则被外部压力扰动激发。

The interaction between a columnar vortex and external turbulence is investigated numerically. A Lamb-Oseen vortex is immersed into initially isotropic homogeneous turbulence, which, itself, is produced numerically by a direct numerical simulation of decaying turbulence. The formation of inhomogeneous fine turbulent eddies around the columnar vortex and the vortex-core deformations are studied in detail, by visualizing the flow field. The initially random turbulent eddies (worms) are wrapped around the columnar vortex, and become like vortex rings (or sprirals). Statistical quantities, such as two-point-energy-spectrum and two-point-enstrophy spectrum, are evaluated by averaging 20 realizations and compared with the theoretical predictions by a. rapid distortion theory (RDT). The axial velocity correlation dominates near the vortex surface, whereas the radial velocity correlation becomes larger, where the worms are wrapped. If the columnar vortex is strong compared with the external turbulence, external velocity disturbances are blocked by the vortex and they cannot penetrate into the vortex core directly, whereas various types of vortex waves (Kelvin waves) are excited by the external pressure disturbances.