Relaxation of Spatially Advancing Coherent Structures in a Turbulent Curved Channel Flow
Relaxation of Spatially Advancing Coherent Structures in a Turbulent Curved Channel Flow
复制标题
DOI：
10.1115/1.4024591
复制
发表时间：
2013-09
影响因子：
2
通讯作者：
K. Matsubara;T. Ohishi;K. Shida;T. Miura
中科院分区：
文献类型：
--
作者：
K. Matsubara;T. Ohishi;K. Shida;T. Miura
对180°弯曲通道内的不可压缩湍流进行了直接数值模拟，该弯曲通道具有与其出口相连的长直部。考察了有组织的相干涡旋在弯曲通道中如何生长和衰减：半径比为0.92，长宽比为7.2，后续直线段长度为通道半宽的75倍。 1552 × 91 × 128 ( = 18,427,136) 个网格被分配到计算域。基于摩擦速度的雷诺数保持在 150，以解析包括弯曲和直线区域的长域。与相干涡沿着凹壁生长不同，在曲率之后凸壁侧的涡仍然很强，伴随着凸壁附近小尺度湍流的尾部。相干涡流的出现和消失之间的差异本质上来自于平均压力梯度，它在曲率入口和出口之间相反地帮助或避免近壁流体。平均流在凸壁入口附近减速，从而使流不稳定并触发相干涡流的开始。相反，平均流在凸壁出口附近加速，减弱相干涡流，在凹壁出口附近减速，增强湍流。因此，在曲率的入口和出口之间，湍流增强和衰减相反，并且相干涡流在凸侧而不是在其开始的凹侧绘制尾流。
A direct numerical simulation is made for the incompressible turbulent flow in the 180 deg curved channel with a long straight portion connected to its exit port. An examination is made for how the organized coherent vortex grows and decays in the curved channel: the radius ratio of 0.92, the aspect ratio of 7.2, and the succeeding straight section length of 75 times the channel half width. The 1552 × 91 × 128 ( = 18,427,136) grids are allocated to the computational domain. The frictional-velocity-based Reynolds number is kept at 150 to resolve the long domain including curved and straight regions. In contrast to that the coherent vortex grows along the concave wall, the vortex remains strong in the convex-wall side after the curvature accompanying a tail of the small-scale turbulence near the convex wall. The dissimilarity between the onset and disappearing of the coherent vortex essentially comes from the mean pressure gradient, which aids or averts the near-wall fluid oppositely between the curvature inlet and the exit. The mean flow is decelerated near the inlet of the convex wall to destabilize the flow and to trigger the onset of the coherent vortex. Contrary, the mean flow is accelerated near the exit of the convex wall to weaken the coherent vortex, and is decelerated near the exit of the concave wall to enhance the turbulence. Therefore, the turbulence enhancement and attenuation occurs oppositely between the inlet and exit of the curvature, and the coherent vortex draws a wake in the convex-side rather than the concave-side where it starts.