Experimental study on characteristics of flow around single cylinder in microchannel based on Micro-PIV

doi:10.11949/0438-1157.20190853

Abstract

Abstract:

The micro-particle imaging velocimetry(Micro-PIV) system was used to investigate the characteristics of the flow around a microcylinder with D=0.4 mm in the microchannel in the range of 6<Re<300. The velocity field, vorticity field, turbulence intensity field and the vortex structures in flow layers with different heights under different Reynolds numbers were obtained and analyzed. The research results show that the first critical Re of the vortex around the micro-cylinder is around 10, and with the increase of Re, the length and width of the vortex in the wake region increase, the wake region increases, and the center of the vortex moves backward. As the increase of Reynolds number, the length and width of the vortices increased, and the center of the vortices moved downstream. The wake regions in flow layers with different heights had the same length, but the vortex center of the wake region moved downstream for flow in a layer away from the wall. The high vorticity area and the high turbulence intensity area were distributed on both sides of the microcylinder, indicating that the fluid mixing at this position was more severe. With the increase of Re, the vorticity increased, and the high vorticity area became narrower and longer, as well as the turbulence intensity. Besides, the high turbulence intensity area expanded with increase of Re. and the turbulence intensity difference among different flow layers was small at Re>200.

Key words: flow around microcylinder, Micro-PIV, wake region, vorticity, turbulence intensity

摘要：

采用微观粒子成像系统（Micro-PIV）实验研究了6<Re<300范围内微通道内D=0.4mm圆柱的绕流特性，获得并分析了不同Re下不同高度流层的速度场、涡量场、湍流强度场及回流区漩涡结构。研究结果表明，微圆柱绕流出现漩涡的第一临界Re在10左右，随着Re的增大，尾流区涡长度和宽度增加，尾流区域增大，漩涡中心后移；由于黏性阻滞，越靠近微通道壁面，主流速度越低且分布越均匀；不同高度下回流区长度相同，远离壁面的平面尾流区漩涡中心沿流动方向后移；高涡量区与高湍流强度区分布在微圆柱两侧，说明该位置流体混合较为剧烈，随着Re的增大，涡量增加，高涡量区变窄、变长，湍流强度及高湍流强度区域增大，当Re>200，不同高度流层的湍流强度差别较小。

关键词: 微圆柱绕流, Micro-PIV, 尾流区, 涡量, 湍流强度

CLC Number:

TK 124

Jichao LI, Can JI, Mingming LYU, Jing WANG, Zhigang LIU, Huijun LI. Experimental study on characteristics of flow around single cylinder in microchannel based on Micro-PIV[J]. CIESC Journal, 2020, 71(4): 1597-1608.

李济超, 季璨, 吕明明, 王静, 刘志刚, 李慧君. 微通道内单柱绕流特性的Micro-PIV实验研究[J]. 化工学报, 2020, 71(4): 1597-1608.

Figures/Tables 12

Fig.1 Schematic diagram of experimental system

Fig.2 Schematic diagram of test section

Fig.3 Schematic diagram of microchannel and microcylinder

Fig.4 Gray scale image of tracer particles

Table 1 Uncertainties of measured parameters

Parameter	Uncertainty
U_avg	±2.09%
Re	±2.15%
W_z	±4.00%
L_vc	±4.47%
L^*	±4.47%
TI	±4.00%
U	±6.02%
V	±6.02%

Fig.5 Time-averaged velocity field at different plane for different Re

Fig.6 Schematic diagram of boundary layer separation for circular cylinder flow

Fig.7 Dimensionless length of vortex at different Reynolds numbers

Fig.8 Center location of vortex at different Reynolds numbers

Fig.9 Dimensionless time-averaged velocity distribution in wake at different Re

Fig.10 Dimensionless time-averaged vorticity field at different plane for different Re

Fig.11 Dimensionless turbulence intensity field at different plane for different Re

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