论文标题
边界层中的Langmuir型涡旋,由纵横交错的波浪形墙壁形态驱动
Langmuir-type vortices in boundary layers driven by a criss-cross wavy wall topography
论文作者
论文摘要
我们研究了一种操纵壁挂流动的机制,从而使墙壁形状的波状波动驱动了定制纵向涡流的产生。不受干扰的剪切流的环境涡度与墙壁地图强制强制的流线的旋转之间的共振相互作用可稍微旋转平均流动的旋转涡度进入流向流向流动方向,从而形成了常规流卷的形式,形成了旋转运动。该过程是运动学的,与Craik(1970)提出的Langmuir循环(LC)的“直接驱动” CL1机制基本相同。边界层是通过选择合适的主要流量剖面来建模的。在两个渐近方案中发现了一个简单的,易于整合的表达式:在两个渐近方案中发现了本质上无粘性不稳定性的谐振,以及完全开发的稳态粘性流。在幂律剖面的特殊情况下,获得了波动边界上流量的线性订购溶液。这些解决方案使我们能够快速绘制对边界设计参数的循环响应。该研究补充了直接的数值模拟,这些模拟验证了边界引起的langmuir涡流的表现,该层流在没有滑移边界的层流流中。模拟与理论显示出良好的定性协议。在数量上,比较取决于扰动理论中采用的位移长度闭合参数。虽然壁驱动的LC在湍流中似乎变得不稳定,但我们建议该机制可以促进边界层中的旋转运动,这是一种流动特征,据报道,在某些情况下据报道会减少阻力。
We investigate a mechanism to manipulate wall-bounded flows whereby wave-like undulations of the wall topography drives the creation of bespoke longitudinal vortices. A resonant interaction between the ambient vorticity of the undisturbed shear flow and the undulation of streamlines enforced by the wall topography serves to slightly rotate the spanwise vorticity of the mean flow into the streamwise direction, creating a swirling motion, in the form of regular streamwise rolls. The process is kinematic and essentially identical to the `direct drive' CL1 mechanism for Langmuir circulation (LC) proposed by Craik (1970). Boundary layers are modelled by selecting suitable primary flow profiles. A simple, easily integrable expression for the cross-plane stream function is found in two asymptotic regimes: the resonant onset of the essentially inviscid instability at early times, and the fully developed steady state viscous flow. Linear-order solutions for flow over undulating boundaries are obtained, fully analytical in the special case of a power-law profile. These solutions allow us to quickly map out the circulation response to boundary design parameters. The study is supplemented with direct numerical simulations which verify the manifestation of boundary induced Langmuir vortices in laminar flows with no-slip boundaries. Simulations show good qualitative agreement with theory. Quantitatively, the comparisons rest on a displacement length closure parameter adopted in the perturbation theory. While wall-driven LC appear to become unstable in turbulent flows, we propose that the mechanism can promote swirling motion in boundary layers, a flow feature which has been reported to reduce drag in some situations.