An experimental study of fluctuating lift on a square-section cylinder oscillating transversely in a uniform stream

Experiments on a square-section cylinder fixed and forced to oscillate transversely in a uniform stream were conducted in a water tank. The Reynolds number of the experiments is in the range of 3·10³ to 10⁴, the amplitude to side length ratioA/D is up to 0.7 and the range of reduced velocity is 4.5<V _r <12. This study aims at investigating the lock-in phenomenon, the fluctuating lift and the phase shift between fluctuating lift and displacement of the oscillating cylinder. The problems on the aeroelastic instability relating to present experimental results have been discussed. The flow visualization clearly shows that there are drastic changes of vortex-shedding from cylinder at the resonance point and the upper end of the lock-in range. The results of the flow visualization give better understanding of the physical mechanism of the phase shift. Project supported by National Natural Science Foundation of China     

旋转方形散射体对三角晶格磁振子晶体带结构的优化

用改进的平面波展开法数值计算了正方形散射体三角排列的二维磁振子晶体当散射体旋转时的带结构. 结果显示, 同样的填充率下, 旋转正方柱散射体可以在新的频率范围内打开更多的带隙, 或者使低频带隙加宽. 说明旋转散射体可以有效地优化带隙.     

Numerical and experimental investigation of flow over a semicircular weir

The water flow over a semicircular weir is investigated numerically and experimentally in this paper. The numerical model solves the Reynolds equation for a mean flow field with thek-ε-turbulent model. To trace the motion of the free surface, the COF method with geometric reconstruction is employed. The velocity of the flow is measured by means of LDV technique. Four types of flow patterns, the position of the separation and reattachment point, the distribution of shear stress on the bed at downstream of the weir are presented and discussed. The numerical results agree well with the experiment data.     

圆柱绕流局部冲刷机制的实验研究

采用粒子图像测速技术和粒子图像识别技术研究了冲刷坑的演化过程及局部冲刷的流体动力机制。首先研究了动床条件下圆柱周围的床面演化过程,给出垂直对称面输沙率随时间变化以及圆柱下游垂直对称面的沙颗粒浓度和泥沙分布规律;其次针对典型冲刷坑形状固定底床,测量了圆柱下游的瞬时流场,并给出平均流场。结果表明尾流区平均剪应力较低,但垂向涡量和湍流强度较高。分析指出平均剪应力较低的尾流区域,局部冲刷的主要动力机制是尾涡和湍流的综合作用。     

规则波作用下垂直圆柱局部波浪力

在ＫＣ为４０～３５，雷诺数Ｒｅ为６×１０３～２×１０４参数范围内就规则波作用下垂直圆柱局部波浪力进行了实验研究．给出横向力随ＫＣ数类型变化的划分．基于Ｓｔｏｋｅｓ二阶波理论和Ｍｏｒｉｓｏｎ公式得到圆柱阻力系数ＣＤ，惯性力系数ＣＭ和最大升力系数ＣＬｍａｘ沿桩柱的分布及其随ＫＣ数的变化规律．结果表明，在波表面间歇区的桩柱的局部水动力系数变化显著，越向波峰位水动力系数ＣＤ和ＣＬｍａｘ越减小，而ＣＭ值却越增高．