论文标题
遥远的湍流斑点
Far field of turbulent spots
论文作者
论文摘要
亚临界壁结合的剪切流中湍流的增殖涉及空间局部的相干结构。湍流斑点对应于有限的时间非线性响应对尖锐的干扰，并被视为过渡过程中湍流的种子。湍流波动的快速空间衰减远离位置，并伴随着具有稳健结构的大规模流动。这些斑点的远场速度场是在四个不同流动场景中的大域中的光谱方法（平面couette，plan poiseuille，couiteuille，couette-poiseuille和sinosoidal剪切流）进行数字研究的。与以前的期望相反，速度场衰减的平面成分是代数的。这些衰减指数仅取决于系统的对称性，在这里，这些指数取决于应用梯度的存在，而不取决于雷诺数。这表明远场的有效二维多极扩展由偶极流量组成或不对称流动场主导。
The proliferation of turbulence in subcritical wall-bounded shear flows involves spatially localised coherent structures. Turbulent spots correspond to finite-time nonlinear responses to pointwise disturbances and are regarded as seeds of turbulence during transition. The rapid spatial decay of the turbulent fluctuations away from a spot is accompanied by large-scale flows with a robust structuration. The far field velocity field of these spots is investigated numerically using spectral methods in large domains in four different flow scenarios (plane Couette, plane Poiseuille, Couette-Poiseuille and a sinusoidal shear flow). At odds with former expectations, the planar components of the velocity field decay algebraically. These decay exponents depend only on the symmetries of the system, which here depend on the presence of an applied gradient, and not on the Reynolds number. This suggests an effective two-dimensional multipolar expansion for the far field, dominated by a quadrupolar flow component or, for asymmetric flow fields, by a dipolar flow component.
