Unstable turbulent channel flow response to spanwise-heterogeneous heat fluxes: Prandtl’s secondary flow of the third kind
Unstable turbulent channel flow response to spanwise-heterogeneous heat fluxes: Prandtl’s secondary flow of the third kind
复制标题
不稳定湍流通道流对展向非均质热通量的响应：第三类普朗特二次流
DOI：
10.1017/jfm.2022.15
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发表时间：
2022
影响因子：
3.7
通讯作者：
Calaf, M.
中科院分区：
文献类型：
--
作者：
Salesky, S.;Anderson, W.;Calaf, M.
湍流二次流被定义为普朗特的第一类或第二类二次流，前者由涡量的拉伸和/或倾斜产生，后者由雷诺应力的空间不均匀性产生。这两种机制都是瞬时活跃的惯性占主导地位的壁湍流;雷诺应力的空间异质性所需的雷诺平均二次流。展向变化的表面粗糙度可以引起展向壁面法向平面中的湍流应力空间不均匀性，并为流向对齐的平均二次流提供支撑。在这里，我们证明，湍流二次流也可以维持展向变化的表面热通量在不稳定分层湍流通道，下文定义为普朗特的第三类二次流。支持这一机制建立与缩放参数，而大涡模拟是用来模拟惯性主导的通道湍流响应的下边界均匀的空气动力学/流体动力学粗糙度，但展向可变的表面热通量。流向涡量和湍流动能的输运方程改变了总流响应，因此是一种明显不同的机制，负责维持二次流。
Turbulent secondary flows are defined as Prandtl's secondary flow of the first or second kind, the former produced by stretching and/or tilting of vorticity, the latter produced via spatial heterogeneity of Reynolds stresses. Both mechanisms are instantaneously active within inertia-dominated wall turbulence; Reynolds stress spatial heterogeneity is required for Reynolds-averaged secondary flows. Spanwise-variable surface roughness can induce turbulent stress spatial heterogeneity in the spanwise–wall-normal plane and provide sustenance for streamwise-aligned mean secondary flows. Herein, we demonstrate that turbulent secondary flows can also be sustained by spanwise variability in the surface heat flux in unstably stratified turbulent channels, defined hereafter as Prandtl's secondary flow of the third kind. Support for this mechanism is established with scaling arguments, while large-eddy simulation is used to model inertia-dominated channel turbulence responding to a lower boundary with uniform aerodynamic/hydrodynamic roughness but spanwise-variable surface heat flux. Transport equations for streamwise vorticity and turbulent kinetic energy, alters aggregate flow response and thus is a distinctly different mechanism responsible for sustenance of secondary flows.