On coherent-vortex identification in turbulence
On coherent-vortex identification in turbulence
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DOI：
10.1088/1468-5248/1/1/011
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发表时间：
2000-12-18
影响因子：
1.9
通讯作者：
Delcayre, F
中科院分区：
文献类型：
--
作者：
Dubief, Y;Delcayre, F
在湍流直接数值模拟（DNS）和大涡模拟（LES）的基础上研究了相干涡的识别问题。首先表明，在均匀密度流中，由凸等压面包围的小截面低压管内，拉普拉斯压力为正。由于该量与 delu 的第二个不变量 Q 有关，因此 Q 准则（Q 为正的区域）是此类管存在的必要条件。该导出方案与各向同性湍流不可压缩模拟中的其他经典方法进行了比较：混合层、通道流和向后的步骤。 Q 等值面显示出非常漂亮的相干涡旋。该准则还与条件采样方法结合使用，讨论受控通道流中准纵向涡的特征。近壁涡旋结构对速度和涡度波动的贡献明显是孤立的。最后，将 Q 准则应用于分离流中 Lambda 涡流的引出。针对不可压缩的后向台阶和经过矩形腔的跨音速流，讨论了这些结构的动力学。
The identification issue of coherent vortices is investigated on the basis of direct numerical simulation (DNS) and large-eddy simulations (LES) of turbulent flows. It is first shown that the pressure Laplacian is positive within a low-pressure tube of small cross section enclosed by convex isobaric surfaces in a uniform-density flow. Since this quantity is related to the second invariant Q of delu, the Q criterion (region where Q is positive) is a necessary condition for the existence of such tubes. This eduction scheme is compared to other classical methods in incompressible simulations of isotropic turbulence: a mixing layer, a channel flow and a backward-facing step. Q-isosurfaces turn out to display very nice coherent vortices. This criterion is also used in combination with a conditional sampling method to discuss the characteristics of quasi-longitudinal vortices in a manipulated channel flow. The contribution of near-wall vortical structures to velocity and vorticity fluctuations is clearly isolated. Finally, the Q criterion is applied to the eduction of Lambda vortices in separated flows. The dynamics of these structures is discussed for an incompressible backward-facing step and a transonic flow past a rectangular cavity.