论文标题

使用无压力边界条件控制泰勒 - 库特流中的次要流

Controlling secondary flows in Taylor-Couette flow using stress-free boundary conditions

论文作者

Jeganathan, V., Alba, K., Ostilla-Mónico, R.

论文摘要

Taylor-Couette(TC)流动,两个独立旋转和同轴圆柱之间的流量通常用作剪切流的规范模型。与平面库特不同,可以在TC流中找到固定的二次流。这些被称为泰勒卷,并极大地影响流动行为。我们研究了使用无压力和无滑动圆柱条件的模式来修改这些二级结构的可能性。为此,我们对窄间隙TC流进行直接数值模拟,并在四个不同的剪切reynolds数字上使用纯内圆柱旋转,最高$ re_s = 3 \ times 10^4 $。我们发现,一维方位角模式对流动拓扑没有显着影响,并且在完全无滑动的情况下,所得的扭矩是大的扭矩($ \ sim80-90 \%$)。一维的轴向图案会降低扭矩,并且对于某些图案频率,通过干扰现有的雷诺(Reynolds)强调产生二级结构的应力。对于$ re \ geq 10^4 $,这种中断导致的扭矩要比简单的边界层效应以及产生的有效滑动长度和滑动速度所期望的扭矩较小。我们发现二维棋盘格模式具有与方位角模式相似的行为,并且不会实质上影响流动或扭矩,但是二维螺旋不均匀性可以围绕固定的二次流动,因为它们诱导持续的轴向速度。我们量化了滚动的运动的各个角度和螺旋模式的宽度,并找到非单调的行为作为模式角度和模式频率的函数。

Taylor-Couette (TC) flow, the flow between two independently rotating and co-axial cylinders is commonly used as a canonical model for shear flows. Unlike plane Couette, pinned secondary flows can be found in TC flow. These are known as Taylor rolls and drastically affect the flow behaviour. We study the possibility of modifying these secondary structures using patterns of stress-free and no-slip boundary conditions on the inner cylinder. For this, we perform direct numerical simulations of narrow-gap TC flow with pure inner cylinder rotation at four different shear Reynolds numbers up to $Re_s=3\times 10^4$. We find that one-dimensional azimuthal patterns do not have a significant effect on the flow topology, and that the resulting torque is a large fraction ($\sim80-90\%$) of torque in the fully no-slip case. One-dimensional axial patterns decrease the torque more, and for certain pattern frequency disrupt the rolls by interfering with the existing Reynolds stresses that generate secondary structures. For $Re\geq 10^4$, this disruption leads to a smaller torque than what would be expected from simple boundary layer effects and the resulting effective slip length and slip velocity. We find that two-dimensional checkerboard patterns have similar behaviour to azimuthal patterns and do not affect the flow or the torque substantially, but two-dimensional spiral inhomogeneities can move around the pinned secondary flows as they induce persistent axial velocities. We quantify the roll's movement for various angles and the widths of the spiral pattern, and find a non-monotonic behaviour as a function of pattern angle and pattern frequency.

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