圆柱振荡流中的斜向涡街

Oblique vortex street from a cylinder oscillating in water

本文用数字粒子成像测速仪 (DPIV) ,对圆柱体在静水中作正弦振动而产生的振荡流场进行了实测研究。通过相位锁定技术和互相关分析法 ,分别获得了圆柱体在振动周期中 8个不同相位的流场速度矢量及涡量强度等值线分布。实测表明 ,当 KC =12 时 ,圆柱振荡尾流中将存在一个有明显周期性且较规则的斜向涡街 ,涡街主要由一股较强的二次流及其两侧的非对称的涡对构成 ,涡街与圆柱体振动方向成± 45°夹角。而当KC =6.2 8时 ,由于吸附于柱体的涡对未能脱离柱体进入其尾流 ,因而无涡街产生。文中还分析和讨论了斜向涡街产生的机理并对振荡流中柱体受力情况进行了量测。受力测量结果表明 :当斜向涡街稳定时 ,圆柱体各向受力差异不大 ;但在涡街方向转变期间 。

Digital particle image velocimetry (DPIV) was applied to investigate the flow field around a circular cylinder undergoing sinusoidal oscillating movement in still water. Velocity vectors and vorticity contours were obtained at eight successive phases of the oscillating cycle at Keulegan-Carpenter number KC=12 and KC=6.28. The generation, shedding and movement of the single pair vortex street formed in the wake were revealed and discussed. It is found that the vortex street accompanied by a biased flow stream at KC=12 is inclined at about ±45° angle to the direction of the cylinder movement. Another set of experiments were perfomed at KC=6.3 and the results show the absence of an oblique vortex street at this lower KC number. The measured result of the forces on cylinder indicates that while the flow direction of an oblique vortex street is changing, the oblique force is larger obviously than the in-line force.