Passive methods of flow and cavitation control appear to offer some of the best prospects in the field of hydraulic engineering and marine applications. In this article, we aimed at an experimental examination of the effect of wall roughness/wettability on the occurrence of cavitation and turbulence structure in the cross flow around and in the wake of a circular cylinder in two characteristic regimes. For this, we used three test bodies with different surface morphologies: smooth (reference), micro-scale irregularities (rough) and regular large-scale (of the order of a millimeter) texture (finned). Using high-speed imaging to observe vapor cavities, we revealed that cavitation is noticeably suppressed by both types of roughness. Applying the method of vapor phase detection (Pervunin et al., 2021), this finding was then quantitatively confirmed through an in-depth analysis of an ensemble of instantaneous velocity fields measured by PIV, indicating that modification of wall morphology is an effective method of cavitation control. The procedure of statistical vector filtration (Heinz et al., 2004) allowed us to remove outliers from the velocity fields and, thus, calculate various turbulence characteristics, including higher-order moments (i.e., the coefficients of skewness and excess). Wall irregularities were found to significantly affect the turbulence structure of the wake flow, but the higher-order moments downstream of the modified-surface cylinders turned out to be unexpectedly insensitive to a change in the flow regime, as opposed to the smooth one. Regardless of the type of surface morphology, the influence of roughness on the mechanism of formation of large-scale vortices and their characteristics was weakened. However, it caused overall disorganization of liquid motion in the cylinder wake, thus making local flow conditions highly unsteady. In addition, this process became more chaotic with an increase in the scale of irregularities.

中文翻译：

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圆柱绕流中的空化抑制和湍流结构转化：表面形貌和润湿性效应


流动和空化控制的被动方法似乎在水利工程和海洋应用领域提供了一些最好的前景。在本文中，我们旨在通过实验检查壁粗糙度/润湿性对两种特征状态下圆柱体周围和尾流中的空化和湍流结构发生的影响。为此，我们使用了三种具有不同表面形态的测试体：光滑（参考）、微尺度不规则（粗糙）和规则大尺度（毫米级）纹理（翅片）。使用高速成像观察蒸汽腔，我们发现两种类型的粗糙度都显着抑制了空化。应用气相检测方法（Pervunin et al., 2021），通过对 PIV 测量的瞬时速度场集合的深入分析定量证实了这一发现，表明改变壁面形态是一种有效的方法。空化控制。统计矢量过滤过程（Heinz 等人，2004）使我们能够从速度场中去除异常值，从而计算各种湍流特征，包括高阶矩（即偏度系数和过量系数）。人们发现壁不规则性会显着影响尾流的湍流结构，但与平滑的情况相反，表面改性圆柱体下游的高阶矩对流态的变化出乎意料地不敏感。无论何种类型的表面形貌，粗糙度对大尺度涡形成机制及其特征的影响均减弱。 然而，它导致气缸尾流中液体运动的整体混乱，从而使局部流动条件高度不稳定。此外，随着违规规模的扩大，这一过程变得更加混乱。