【作者】 李强；

【导师】 张土乔； 朱志伟；

【作者基本信息】 浙江大学 ， 市政工程， 2014， 硕士

【摘要】 圆柱绕流问题广泛存在于工程实际中。流体流经圆柱形构筑物时,构筑物后方会产生卡门涡街,并伴随周期性的阻力和升力震荡,严重时会引起构筑物的共振破坏。本文对多圆柱柱群绕流问题进行了物理实验和数值模拟研究,研究内容着重于柱群后方的整体流态及柱群受到的总升阻力。本次研究的柱群由19个相同的小圆柱组成,实验中对五种不同直径比的柱群尾流进行了定点流速的测量,给出了尾流纵向和横向部分断面的速度分布和湍流强度分布,并计算了尾流中的脱涡频率。使用流动可视化方法研究了尾流表面流场和间隙流流动规律。对应物理实验建立了数值模型,按照相同的边界条件对实验中的工况进行了模拟,给出了柱群尾流的涡量分布图,并对柱群中每一个圆柱进行了升阻力系数的监控。结果发现小直径比柱群的尾流中剪切层按固定频率脱落,流动类似于单柱绕流。大直径比柱群尾流中不存在以固定频率脱落的剪切层,但其总升阻力系数却随时间呈周期性变化,其尾流流速恢复慢,对周边自由流的卷吸作用小。最后,本文通过改变雷诺数,对不同来流条件下的柱群绕流进行了数值模拟研究。给出了群尾流中的涡量分布以及水动力学参数随来流流速的变化关系。更多还原

【Abstract】 Flow around a circular cylinder exists in a lot of engineering practice. Karman Vortex Street will be produced when the fluids flow around the cylindrical structures. The periodic lift force and drag force that the structures suffered may caused resonance and destroy the structures. Flow around a cylinder group was investigated experimentally and numerically in this study. The investigation was mainly focused on the flow patterns behind the cylinder group and the hydrodynamic parameters of the cylinder group.The cylinder group was consisted of19identical cylinders in this study. Five different diameter ratios was tested. The distribution of longitudinal time-averaged velocity and turbulence intensity was measured, and the frequency of the separating shear layers was calculated. Flow visualization methods were used to visualize the surface flow field and the gap flow. The numerical model was built as the experiment. The vorticity distribution of the wake was calculated, as well as the lift coefficient and drag coefficient of each cylinders of the group. The results show that the shear layers behind the cylinder groups with small diameters ratios separated with fixed frequency, the flow pattern was similar to that of a single cylinder. No fixed frequency was found in the wake behind the cylinder groups with large diameter ratios. However, the lift force and drag force changed with a fixed frequency. For the cylinder groups with large diameter ratios, The velocity recovered more slowly, and entrainment effect to the surrounding fluid was weaker for the cases with large diameter ratios.Finally, flow around a cylinder group with different Reynolds numbers was investigated numerically. The vorticity distribution of the wake was calculated, the curves of hydrodynamic parameters over velocity of coming flow were presented.更多还原