Computational analysis of the two-dimensional–three-dimensional transition in forward-facing step flow
Computational analysis of the two-dimensional–three-dimensional transition in forward-facing step flow
复制标题
前向台阶流中二维-三维转变的计算分析
DOI：
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发表时间：
2003
影响因子：
3.7
通讯作者：
L. Kleiser
中科院分区：
文献类型：
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作者：
D. Wilhelm;C. Härtel;L. Kleiser
结果是通过对平面通道中前向台阶上的流动进行计算研究得出的。该研究的目的是更好地了解通常在台阶和肋上以及类似配置中的流动分离区域中观察到的三维度。我们根据迎面流动的台阶高度和体积速度考虑雷诺数为 330 的层流，并且假定台阶在翼展方向上无限延伸。使用混合光谱/光谱元素代码进行高分辨率模拟。此外，还对台阶处的流动进行了线性稳定性研究。结果表明，在所考虑的情况下，三维度与台阶前面的分离气泡的某些绝对不稳定性无关；相反，它是水流对迎面而来的水流中存在的三维扰动的敏感反应。结果表明，小于平均流量 1% 的扰动幅度（例如，在台阶前面 10 个台阶高度处）已经足以产生分离区的可见三维结构。如果系统地降低扰动水平，三维状态就会演变成几乎二维的再循环。这里的关键发现是，流动响应的强度与流入扰动的幅度成正比，这意味着台阶区域中流动的破碎是二维基流的线性（即小）扰动。当前模拟结果与实验数据的比较表明，在台阶区域中的流动拓扑以及下游形成的特征条纹的翼展方向间距等方面，结果非常一致。
Results are presented from a computational study of the flow over a forward-facing step in a plane channel. The aim of the study is to gain better insight into the three-dimensionality that is typically observed in the separation region of flows over steps and ribs, and in similar configurations. We consider laminar flow at a Reynolds number of 330, based on step height and bulk velocity of the oncoming flow, and the step is assumed to be infinitely extended in the spanwise direction. High-resolution simulations are undertaken using a mixed spectral/spectral-element code. Moreover, a linear stability study of the flow at the step is performed. The results show that, in the case considered, the three-dimensionality is not related to some absolute instability of the separation bubble in front of the step; rather, it is a sensitive reaction of the flow to three-dimensional perturbations present in the oncoming stream. It is demonstrated that disturbance amplitudes of less than 1% of the mean flow (at, say, 10 step heights ahead of the step) already suffice to produce a visibly three-dimensional structure of the separation zone. If the disturbance level is systematically decreased, the three-dimensional state evolves to an almost two-dimensional recirculation. Here, the key finding is that the intensity of the flow response is proportionate to the amplitude of the inflow disturbance, meaning that the breakup of the flow in the step region is a linear (i.e. small) perturbation of the two-dimensional base flow. A comparison of the present simulation results with experimental data shows close agreement concerning, for example, the flow topology in the step region, and the spanwise spacing of the characteristic streaks that form further downstream.