A test for the wake vortex of a flexible oscillating caudal fin is carried out with Digital Particle Image Velocimetry(DPIV),and the variation of vortex distance and the vorticity in the range of oscillating frequency from 0.704 Hz to 1.17 Hz are analyzed.It is found that with the increase of the oscillating frequency,the vortex distance decreases and the peak of the vorticity increases,When the Strouhal number is smaller than 0.49,a larger thrust component is obtained.The distribution of the velocity circulation and the vortex distance in the different spanwise section of the caudal fin are given,and then the dimension of the vortex ring is determined. The radius of the vortex ring is 79.3 mm and the average velocity circulation is 28152.9 mm2/s at the oscillating frequency of 0.835 Hz.The model of 3-D vortex ring chain of flexible oscillating caudal fin is constructed based on the information of wake vortex field. Finally,an effective analysis method is provided for establishing the relationship of oscillating parameters for the caudal fin and the wake structure and the intrinsic mechanism of efficient fish swimming is investigated.
利用计算流体力学软件 Fluent 开展了三维动波浪壁圆柱绕流的数值模拟，建立了三维运动波浪壁圆柱模型，通过 C语言自编程序实现波浪壁面的运动控制，并保证壁面变形时网格的高质量。在来流速度 u ＝0.125 m/ s、雷诺数 Re ＝12500的情况下，开展了动波浪壁波动速度 w＝0、0.0625、0.125、0.1875 m/ s 四个工况的计算分析，并比较了不同波动速度对流场结构、升力、阻力特性的影响。结果表明：动波浪壁圆柱能有效抑制流动的分离，消除交替脱落的尾涡，从而消除周期振荡的升力；在消除卡门涡街的同时，圆柱后驻点处的涡量值随波动速度增加而增加，其原因在于波形移动加大了壁面流体的速度，从而减小了圆柱前后的压力差，减小了阻力；随着波动速度的增大，平均阻力系数呈明显下降趋势，当波动速度为来流速度的1.5倍时，平均阻力系数相对于光滑圆柱下降了53.76％。
