An experimental study on the vortical structures and behaviour of jets issuing from inclined coaxial nozzles
An experimental study on the vortical structures and behaviour of jets issuing from inclined coaxial nozzles
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DOI：
10.1007/s00348-011-1120-4
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发表时间：
2011-05
影响因子：
2.4
通讯作者：
T. New;E. Tsioli
中科院分区：
文献类型：
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作者：
T. New;E. Tsioli
本文利用激光诱导荧光和粒子图像测速技术对倾斜同轴射流进行了实验研究。内部一次射流和外部二次射流的雷诺数分别为Re = 2500和Re = 500 ~ 2000（根据间隙大小而定），对应的二次与一次射流速度比（VR）为VR = 0.5 ~ 2.0。次主射流面积比为2.25，射流倾角分别为45°和60°。流动可视化显示，在VR = 0.5时，形成了相对独立的倾斜的一次和二次射流涡旋卷缩。在VR = 1.0时，初级射流和次级射流涡旋的规律性配对和合并导致次级射流和周围流体大规模夹带进入初级射流柱，形成“蛇形”轮廓。而在VR = 2.0时，“蛇形”轮廓继续存在，这是次级射流内涡卷缩更强，有规律地“挤压”主射流柱的结果。观察到这些流动行为随着所用倾斜角的增加而加剧。速度测量表明，当速度比和/或倾斜角增加时，倾斜同轴喷嘴促进了一次射流动量向较长的喷嘴长度矢量化。最后，随着喷嘴长度的缩短，由于增强的旋涡相互作用，峰值速度和更高的湍流强度水平也被检测到。
An experimental study on inclined coaxial jets using laser-induced fluorescence and particle image velocimetry is presented here. The Reynolds numbers of the inner primary jet and outer secondary jet were Re = 2,500 and between Re = 500 and 2,000 (based on gap size), respectively, which corresponded to secondary-to-primary jet velocity ratios (VR) of VR = 0.5–2.0. The secondary-to-primary jet area ratio was 2.25, and 45° and 60° incline-angles were studied. Flow visualizations show that relatively independent inclined primary and secondary jet vortex roll-ups were formed at VR = 0.5. At VR = 1.0, regular pairings and mergings between primary and secondary jet vortex roll-ups led to large-scale entrainment of secondary jet and ambient fluids into the primary jet column and conferred a “serpentile”-shaped outline upon it. While the “serpentile”-shaped outline continued to exist at VR = 2.0, it was a result of stronger secondary jet inner vortex roll-ups which “pinched” the primary jet column regularly. These flow behaviours are observed to intensify with an increase in the incline-angle used. Velocity measurements demonstrate that inclined coaxial nozzles promoted vectoring of the primary jet momentum towards the longer nozzle lengths when velocity-ratio and/or incline-angle were increased. Lastly, peak velocity and higher turbulence intensity levels due to augmented vortical interactions are also detected along shorter nozzle lengths.