均匀流作用下并列阶梯圆柱型结构物受力及尾流特性研究

Study on force and wake features of side-by-side stepped circular cylindrical structures in uniform flow

阶梯圆柱是工程中常见的结构外形,其在流场中的受力特征和尾流模式受到直径比的显著影响,机理十分复杂,影响了工程设计受力取值的准确性。针对均匀来流条件下并列阶梯圆柱绕流进行了三维直接数值模拟,选取特定直径比范围(D/d=1.33~2),分析了阶梯圆柱的升阻力特性、尾流模式和旋涡结构等,发现了并列阶梯圆柱绕流流动模式的调制现象,并阐述了其产生机理。研究结果表明,并列阶梯圆柱的尾流模式除受并列圆柱尾流的临近干涉影响外,还受到构成阶梯圆柱的大、小圆柱尾涡相互作用的影响。在小直径比(D/d=1.33)情况下,尾流呈现稳定偏斜(DF)和交替偏斜(FF)的混合模式,窄尾流阶梯圆柱的阻力均值和泄涡频率均较高,宽尾流阶梯圆柱则相反。而在中、大直径比(D/d=1.67和2)情况下,尾流呈现FF模式,两个阶梯圆柱交替出现较高的阻力和泄涡频率,宽、窄尾流呈现不同的旋涡错位连接模式,窄尾流以半环连接和直连为主,而宽尾流则以涡管多连为主。

Stepped circular cylinders are common structural shapes in engineering,whose force characteristics and wake patterns in flow fields are significantly influenced by the diameter ratio,presenting a highly complex mechanism.This complexity affects the accuracy of force values used in engineering design.In this paper,three-dimensional direct numerical simulations of flow past two side-by-side stepped circular cylinders were performed.A specific range of diameter ratio(D/d=1.33-2)was selected,and the lift and drag characteristics,the wake mode,and the vortex structures were analyzed.The wake modulation of the side-by-side stepped cylinders and its mechanism were investigated.The results show that the wake mode of the side-by-side stepped cylinders is influenced not only by the proximity interference of the wakes but also by the interactions between the wakes of the larger and smaller cylinders,consisting of the stepped cylinders.In the case of small diameter ratio(D/d=1.33),the wake shows a combined mode consisting of a stable deflection(DF)mode and an alternating deflection(FF)mode.The mean drag and vortex-shedding frequency of the cylinder with a narrower wake are higher while those of the cylinder with a wider wake are lower.However,in the cases of moderate to large diameter ratios(D/d=1.67 and 2),the wake shows the FF mode.The two stepped cylinders alternately show a higher drag and vortex-shedding frequency.Different vortex dislocations exist in the narrower and wider wakes,with the narrower wake being dominated by half-loop connections and direct connections while the wider wake being dominated by multi-connections.