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首页> 外文期刊>Journal of Fluid Mechanics >Analysis of the flow and mass transfer processes for the incompressible flow past an open cavity with a laminar and a fully turbulent incoming boundary layer
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Analysis of the flow and mass transfer processes for the incompressible flow past an open cavity with a laminar and a fully turbulent incoming boundary layer

机译：分析不可压缩流通过具有层流和完全湍流的进入边界层的开腔的流动和传质过程

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The three-dimensional incompressible flow past a rectangular two-dimensional shallow cavity in a channel is investigated using large-eddy simulation (LES). The aspect ratio (length/depth) of the cavity is L / D = 2 and the Reynolds number defined with the cavity depth and the mean velocity in the upstream channel is 3360. The sensitivity of the flow around the cavity to the characteristics of the upstream flow is studied by considering two extreme cases: a developing laminar boundary layer upstream of the cavity and when the upstream flow is fully turbulent. The two simulations are compared in terms of the mean statistics and temporal physics of the flow, including the dynamics of the coherent structures in the region surrounding the cavity. For the laminar inflow case it is found that the flow becomes unstable but remains laminar as it is convected over the cavity. Due to the three-dimensional flow instabilities and the interaction of the jet-like flow inside the recirculation region with the separated shear layer, the spanwise vortices that are shed regularly from the leading cavity edge are disturbed in the spanwise direction and, as they approach the trailing-edge corner, break into an array of hairpin-like vortices that is convected downstream the cavity close to the channel bottom. In the fully turbulent inflow case in which the momentum thickness of the incoming boundary layer is much larger compared to the laminar inflow case, the jittering of the shear layer on top of the cavity by the incoming near-wall coherent structures strongly influences the formation and convection of the eddies inside the separated shear layer. The mass exchange between the cavity and the main channel is investigated by considering the ejection of a passive scalar that is introduced instantaneously inside the cavity. As expected, it is found that the ejection is faster when the incoming flow is turbulent due to the interaction between the turbulent eddies convected from upstream of the cavity with the separated shear layer and also to the increased diffusion induced by the broader range of scales that populate the cavity. In the turbulent case it is shown that the eddies convected from upstream of the cavity can play an important role in accelerating the extraction of high-concentration fluid from inside the cavity. For both laminar and turbulent inflow cases it is shown that the scalar ejection can be described using simple dead-zone theory models in which a single-valued global mass exchange coefficient can be used to describe the scalar mass decay inside cavity over the whole ejection process.
机译：使用大涡模拟（LES）研究了流经矩形二维浅腔的三维不可压缩流。腔的长宽比（长度/深度）为L / D = 2，由腔深度和上游通道的平均速度定义的雷诺数为3360。腔周围流动对流体特性的敏感性通过考虑两种极端情况来研究上游流动：在空腔上游形成层流边界层，以及上游流动完全湍流时。根据流动的平均统计量和时间物理特性，包括空腔周围区域的相干结构的动力学，对这两种模拟进行了比较。对于层流的情况，发现流动变得不稳定，但是当其在腔上对流时仍保持层流。由于三维流动的不稳定性以及再循环区域内部的射流状流动与分离的剪切层之间的相互作用，规则地从前腔边缘掉落的翼展方向涡流在翼展方向上受到干扰，并且随着它们的接近在后缘拐角处，分成一系列发夹状涡流，这些涡流在靠近通道底部的空腔下游对流。在完全湍流的流入情况下，进入的边界层的动量厚度比层流的流入情况大得多，进入的近壁相干结构在空腔顶部的剪切层的抖动强烈地影响了地层和地层。分离剪切层内部涡流的对流。通过考虑瞬态引入腔体内的无源标量的喷射来研究腔与主通道之间的质量交换。如预期的那样，发现由于湍流涡流之间的相互作用（从空腔的上游对流的涡流与分离的剪切层之间的相互作用），以及由于更大范围的水垢引起的扩散增加，当进入的流体湍流时，喷射更快。填充空腔。在湍流情况下，显示出从空腔上游对流的涡流在加速从空腔内部抽取高浓度流体方面可以发挥重要作用。对于层流和湍流入流情况，都表明可以使用简单的死区理论模型来描述标量喷射，在该模型中，可以使用单值全局质量交换系数来描述整个喷射过程中腔体内的标量质量衰减。 。

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