间隙比对近壁不同钝体涡激振动特性的影响

Effect of gap ratio on vortex-induced vibration characteristics of different blunt bodies near-wall

为研究不同间隙比L/D对近壁单圆柱与单方柱的涡激振动特性的影响,了解尾流对壁面不稳定性的作用机理,搭建了开式循环水槽试验台,利用粒子图像测速(PIV)系统,对过渡流下2种近壁模型进行了试验研究.结果表明:两者具有相似的涡激振动特性,当L/D很小时,钝体下侧剪切层发展受到抑制;随着L/D增大,壁面的抑制作用减弱,尾流处有形成旋涡对的趋势,旋涡逐渐靠近钝体并趋于对称,涡的尺度先增大后减小,近壁面附近流体的加速效应先增强后减弱,且主振频率逐渐减小;两者都呈现出周期性的涡脱运动,但也存在差异,方柱尾流分离点固定,而圆柱不固定;同一Re下,相同L/D下方柱涡的尺度比圆柱更大,近壁面附近的流速也更快;随着L/D增大,圆柱尾流处振幅先增强后减弱,而方柱一直增强且主振频率略小,表明近壁方柱涡脱落周期比圆柱更长.对实际工程领域应用具有一定的参考价值.

In order to study the effect of different gap ratio L/D on the vortex-induced vibration cha-racteristics of a single cylinder and square cylinder near the wall,and to understand the mechanism of wake flow on the wall instability.An open circulating water tank experimental test rig was built,and two near-wall models under transition flow were experimentally studied by using Particle Image Velocimetry(PIV)system.The results show that both have the same vortex-induced vibration characteristics:When L/D is very small,the development of shear layer under blunt body is suppressed.As L/D increases,the suppression effect of the wall is weakened,and there is a tendency to form vortex pairs in the wake.The vortex gradually approaches blunt body and tends to be symmetric.As L/D increases,the acceleration effect of the fluid near the wall first increases and then decreases and there was a tendency to form vortex pairs at the wake.The vortex gradually approaches the blunt body and tends to be symmetrical.The scale of the vortex first increases and then decreases,the acce-leration effect of the fluid near the wall first increases and then decreases,and the main vibration frequency gradually decreases.Both show periodic vortex shedding motion.There are also differences between them.The wake separation point of square cylinder is fixed,while the single cylinder is not.At the same Re,the scale of square cylinder vortex under the same L/D is larger than that of cylinder,and the velocity near the wall is also faster.As L/D increases,the amplitude of the wake of cylinder first increases and then decreases,while square cylinder keeps increasing and the main vibration frequency is slightly smaller,which indicating that the vortex shedding period of near the wall of square cylinder is longer than that of single cylinder.The above research results has certain reference value for practical engineering applications.