Three-dimensionality effects in flow around two tandem cylinders
Three-dimensionality effects in flow around two tandem cylinders
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DOI：
10.1017/s0022112006000139
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发表时间：
2006-07
影响因子：
3.7
通讯作者：
Georgios V. Papaioannou;D. Yue;M. Triantafyllou;G. Karniadakis
中科院分区：
文献类型：
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作者：
Georgios V. Papaioannou;D. Yue;M. Triantafyllou;G. Karniadakis
在层流和早期湍流状态（雷诺数\(Re = 10^2 - 10^3\)）下，对串联排列的两个固定圆柱周围的流动进行了二维和三维直接数值模拟研究。考虑了圆柱之间从\(1.1\)到\(5.0\)倍直径的一系列间距，重点是确定三维性、圆柱间距以及它们的耦合效应。为了实现这一点，我们将二维结果与相应的三维结果进行比较，以及将串联圆柱系统的结果与单个圆柱的结果进行比较。间隙区域中涡旋形成和脱落的临界间距取决于雷诺数。这种依赖性与单个圆柱的形成长度和底部压力吸力随雷诺数的变化有关。这种关联有助于解释二维和三维结果之间的一些差异。三维性的一个主要影响在于临界间距的精确值，这导致涡量场、下游圆柱上的力以及串联系统的脱落频率与二维预测结果存在偏差。二维模拟低估了临界间距，从而在流动性质不同的一系列间距上导致力和脱落频率的错误结果。为了量化三维效应，我们首先采用涡量，将其分解为主要分量和次要分量。主要分量涉及平行于圆柱轴的涡量，而次要分量包含涡量矢量的流向和横向分量。与单个圆柱情况的比较表明，在小于临界值的间距下下游圆柱的存在对主要和次要涡量都有稳定作用。对三维性的系统量化涉及找到力的展向波动强度的度量。这也验证了稳定情况，表明当第二个圆柱放置在小于临界距离时，与单个圆柱情况相比，三维效应受到抑制。然而，当间距超过临界值时，上游圆柱往往表现得像单个圆柱，但流动中的三维性通常会增加。
The flow around two stationary cylinders in tandem arrangement at the laminar and early turbulent regime, ($\hbox{\it Re}\,{=}\,10^2$–$10^3$), is studied using two- and three-dimensional direct numerical simulations. A range of spacings between the cylinders from 1.1 to 5.0 diameters is considered with emphasis on identifying the effects of three-dimensionality and cylinder spacing as well as their coupling. To achieve this, we compare the two-dimensional with corresponding three-dimensional results as well as the tandem cylinder system results with those of a single cylinder. The critical spacing for vortex formation and shedding in the gap region depends on the Reynolds number. This dependence is associated with the formation length and base pressure suction variations of a single cylinder with Reynolds number. This association is useful in explaining some of the discrepancies between the two-dimensional and three-dimensional results. A major effect of three-dimensionality is in the exact value of the critical spacing, resulting in deviations from the two-dimensional predictions for the vorticity fields, the forces on the downstream cylinder, and the shedding frequency of the tandem system. Two-dimensional simulations under-predict the critical spacing, leading to erroneous results for the forces and shedding frequencies over a range of spacings where the flow is qualitatively different. To quantify the three-dimensional effects we first employ enstrophy, decomposed into a primary and a secondary component. The primary component involves the vorticity parallel to the cylinder axis, while the secondary component incorporates the streamwise and transverse components of the vorticity vector. Comparison with the single cylinder case reveals that the presence of the downstream cylinder at spacings lower than the critical value has a stabilizing effect on both the primary and secondary enstrophy. Systematic quantification of three-dimensionalities involves finding measures for the intensity of the spanwise fluctuations of the forces. This also verifies the stabilization scenario, suggesting that when the second cylinder is placed at a distance smaller than the critical one, three-dimensional effects are suppressed compared to the single-cylinder case. However, when the spacing exceeds the critical value, the upstream cylinder tends to behave like a single cylinder, but three-dimensionality in the flow generally increases.