三角形排列圆柱绕流尾流模式及其流体力特性

Wake patterns and hydrodynamic forces of flow around circular cylinders in an equilateral triangular arrangement

该文采用基于嵌入式迭代浸入边界法对等边三角形排列的三圆柱绕流进行了数值模拟研究,其中上游为一个圆柱,下游为并列两圆柱,雷诺数为Re?100,间距比为L*?1.0-6.0。依据流体力特性和旋涡排列的不同,将尾流模式分为6种,分别为单体模式(L*?1.0-1.4)、偏斜模式(L*?1.5-1.9)、FF(Flip-Flopping)模式(L*?2.0-2.5)、反相模式(L*?2.6-2.8和3.5-4.1)、同相模式(L*?2.9-3.4和4.2-4.5)和共同脱涡模式(L*?4.6-6.0)。其中,偏斜模式下,下游两圆柱的间隙流会稳定偏向其中一个圆柱,使得两圆柱的尾流宽度不同,对应的阻力均值也不相等。在上游圆柱剪切层的作用下,FF模式中间隙流偏斜方向切换的时间间隔要明显大于相同雷诺数下并列双圆柱绕流时的情况。为深入研究各尾流模式的特性,分析了不同模式下三圆柱流体力系数的变化情况及其原因。当1.9?L??4.6时,上游圆柱的剪切层进入下游两圆柱的间隙,使得下游两圆柱出现相互吸引。当4.8?L??5.5时,下游两圆柱与上游圆柱脱落旋涡的作用不一致,使得下游两圆柱的流体力系数不相等。

Flow around an equilateral arrangement of three circular cylinders is numerically simulated by using the embeddediteration immersed boundary method. The Reynolds number is Re?100 and the corresponding spacing ratios is L* ?1.0-6.0.Based on the different hydrodynamics and vortex arrangements, six wake patterns are classified as follows, the single bluff-bodypattern(L*?1.0-1.4), the deflected pattern(L*?1.5-1.9), the FF(flip-flopping) pattern(L*?2.0-2.5), the anti-phase pattern(L*?2.6-2.8 & 3.5-4.1), the in-phase pattern(L*?2.9-3.4 & 4.2-4.5) and the co-shedding pattern(L*?4.6-6.0). In thedeflected pattern, the gap flow stably deflects towards one of the downstream cylinders. The wake widths of two downstreamcylinders are different, leading to the different drag coefficients. Due to the existence of the upstream cylinder’s shear layers, theswitching time interval of the gap flow in FF pattern is significantly greater than that in flow around two side-by-side cylinders atthe same Reynolds number. In order to investigate the characteristics of different wake patterns, the variation of the hydrodynamicforces on three cylinders and the underlying mechanism are analyzed. When 1.9? L??4.6, the shear layers of upstream cylinderflow into the gap between two downstream cylinders. Correspondingly, the two downstream cylinders attract each other. When4.8? L??5.5, the hydrodynamic forces on two downstream cylinders are not identical, due to the different vortex interferencesbetween the upstream cylinder and the downstream cylinders.