On the condition of streak formation in a bounded turbulent flow
On the condition of streak formation in a bounded turbulent flow
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DOI：
10.1063/1.858306
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发表时间：
1992-02
影响因子：
4.6
通讯作者：
K. Lam;Sanjoy Banerjee
中科院分区：
文献类型：
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作者：
K. Lam;Sanjoy Banerjee
用傅立叶-切比雪夫伪谱方法对两个表面之间的流动进行了数值研究，其中两个表面可以施加无滑移和自由滑移条件。不同的平均剪切速率被应用于每个边界，以研究剪切和边界条件对在许多先前的研究中观察到的壁面附近的条纹结构的影响。除了在无滑移壁面附近发现的条状结构外，当自由滑移面受到足够高的剪切作用时，计算还揭示了条状结构。在自由滑动表面附近观察到的低速条纹，虽然看起来更明显，但与壁层条纹具有相同的特征。通过运动粘度和适当的剪切速度（在壁面或自由滑移面）进行归一化后，壁面和自由表面附近的条纹之间的平均展向间距约为100。结果表明，在确定主导流动结构时，剪切比边界的性质更重要，这是出乎意料的，因为涡旋线可以在自由滑移边界上附着，而在无滑移边界上则不能。条纹的形成似乎是由一个局部无量纲剪切参数控制的，该参数定义为S≡S‖< u’w’>‖/e，其中S是平均剪切速率，< u’w’>和e分别是运动湍流剪切应力和湍流动能耗散速率。发现S≂1.0是低速条纹区首次出现的条件。
Flow between two surfaces at which no‐slip and free‐slip conditions can be imposed has been investigated numerically with a Fourier–Chebyshev pseudospectral method. Different mean shear rates have been applied to each boundary to study the effect of shear and boundary condition on the streaky structures that have been observed near walls in many previous investigations. In addition to the streaks found near the no‐slip wall, the computations also reveal streaky structures when the free‐slip surface is under a sufficiently high shear. The low‐speed streaks observed near the free‐slip surface, although appearing somewhat more pronounced, have much the same characteristics as the wall‐layer streaks—e.g., the average spanwise spacing between the streaks both near the wall and the free surface is about 100 when normalized by the kinematic viscosity and the appropriate shear velocity (at the wall or at the free‐slip surface). The results show that shear is much more important than the nature of the boundary in determining the dominant flow structure, rather unexpected since vortex lines can attach at a free‐slip boundary whereas they cannot at a no‐slip one. The formation of streaks appears to be governed by a local nondimensional shear parameter defined as S≡S‖〈u’w’〉‖/e, where S is the mean shear rate, and 〈u’w’〉 and e are the kinematic turbulent shear stress and rate of dissipation of turbulent kinetic energy, respectively. It is found that S≂1.0 is the condition at which the elongated low‐speed streaky regions first appear.