An experimental study of coherent swirling vortex rings in a turbulent pulsed jet
An experimental study of coherent swirling vortex rings in a turbulent pulsed jet
复制标题
湍流脉冲射流中相干旋转涡环的实验研究
DOI：
10.1016/j.expthermflusci.2022.110762
复制
发表时间：
2022
影响因子：
3.2
通讯作者：
Chuan He
中科院分区：
文献类型：
--
作者：
H. Fu;Chuan He
采用平面粒子图像测速技术，对Re = 1.0× 104的湍流脉冲射流中的相干涡环进行了实验研究。相干涡环是由步进电机驱动活塞向背景射流中连续喷射流体产生的。涡流是由轴向旋流器产生的，这些旋流器是由三维打印技术制成的，安装在喷嘴后面。实验中产生的旋流数S在0 ~ 1.10范围内，它涵盖了旋流射流的临界旋流数。冲程-喷嘴直径比L/d= 1.56在没有背景射流的单个脉冲射流中产生紧凑的旋流涡环。两个脉冲频率（St= 0.16和0.32），产生相干涡环的调查，与自由射流也测量在相同的Re进行比较。涡环和旋流的组合被发现，以增强湍流脉动强度，这种效果是正相关的涡环（St）和中心回流区（S）的紧凑性。在初始阶段，生成的旋涡环发展到极限，随着S的增大而减小，随着St的增大而增大。达到这一极限的轴向距离随着S和St的增加而减小。然后，环衰减并最终以与S和St成比例地增大的衰减速率消散。此外，在近场中，旋转涡环以其相应的恒定轴向和径向速度演化。轴向速度随S的增大而减小，随St的增大而增大;径向速度随S的增大而增大，与St无关。另外，随着S和St的增大，两个相邻旋流涡环之间的轴向距离减小。此外，轴向距离的时间变化也在较高的S和St下减小，表明轴向传播速度向下游减小。最后给出了涡环核心的详细结构以及涡环卷起过程中产生的相应结构。
This experimental study examines the coherent swirling vortex rings in a turbulent pulsed jet at a Reynolds number R e= 1.0× 10 4 using planar particle image velocimetry. The coherent vortex rings are produced by a stepper-motor-driven piston successively injecting fluid into a background jet flow. The swirl is generated by axial swirlers which are made by three-dimensional printing technology and mounted behind the nozzle. The swirl number S generated in the experiments ranges from 0 to 1.10, which covers the critical swirl number of a swirling jet. The stroke-to-nozzle diameter ratio L/d= 1.56 produces compact swirling vortex rings in a single pulsed jet without a background jet flow. Two pulsing frequencies (St= 0.16 and 0.32) that generate coherent vortex rings are investigated, with the free jet also measured at the same Re for comparison. The combination of vortex rings and swirling flows is found to enhance the turbulent fluctuation intensity; this effect is positively related to the compactness of the vortex rings (St) and central recirculation zone (S). At the early stage, the generated swirling vortex ring develops until it reaches its limit, which decreases as S increases but increases with S t. The axial distance at which this limit is achieved decreases with both increasing S and St. Then, the ring decays and is eventually dissipated at a decay rate that grows larger in proportion to S and S t. Moreover, the swirling vortex rings evolve at their corresponding constant axial and radial velocities in the near field. The axial velocity decreases as S increases and increases with S t, while the radial velocity increases with S and is independent of S t. In addition, the axial distance between two adjacent swirling vortex rings decreases with increased S and S t. Furthermore, the temporal variation of the axial distance also decreases at higher S and S t, indicating that the axial propagation velocity decreases downstream. Finally, detailed structures of the swirling vortex ring cores and the corresponding structures induced by the rolling-up process are presented.
影响因子：
4.6
作者：
Chuangxin He;L. Gan;Yingzheng Liu
通讯作者：
Chuangxin He;L. Gan;Yingzheng Liu