Dynamics of compact vortex rings generated by axial swirlers at early stage
Dynamics of compact vortex rings generated by axial swirlers at early stage
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DOI：
10.1063/5.0004156
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发表时间：
2020-04
影响因子：
4.6
通讯作者：
Chuangxin He;L. Gan;Yingzheng Liu
中科院分区：
文献类型：
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作者：
Chuangxin He;L. Gan;Yingzheng Liu
本文采用平面和立体粒子图像测速技术（PIV）测量和动态延迟分离涡模拟相结合的方法，对雷诺数Re = 20 000时旋流涡环的流动特性进行了研究。特别注意的是大规模的方位角模式的涡环传播过程中的识别。在实验中，涡环是从活塞驱动的轴向旋流器与旋流数范围从S = 0到1.10。冲程比L/D = 1.5用于产生无尾喷流的紧凑涡环。在水槽中进行了PIV测量，得到了纵向中心面上的面内分流速和下游几个位置处的截面上的三分流速。在模拟中，轴向旋流器也被包括在内，而活塞运动是通过施加一个随时间变化的流入条件来实现的。通过平面PIV测量，得到了涡环传播过程中的两种动力学效应：到达时间效应和方位角效应，它们分别引起涡环核的平行移动和涡面的径向倾斜。通过在方位角方向上应用快速傅立叶变换，然后在径向和时间方向上进行适当的正交分解，使用立体PIV结果识别这些模式。结果表明，在弱旋涡环中，m = 0和1模（m为方位波数）共存，而在高旋数时，m = 2模出现，m = 0模衰减。模拟还识别了m = 1和2模式，而m = 2模式相对于形成时间具有大的节距。
This work concentrates on the study of flow dynamics of swirl vortex rings at the Reynolds number Re = 20 000 using a combination of the planar- and stereo-particle image velocimetry (PIV) measurements and dynamic delayed detached-eddy simulation. Particular attention is paid to the identification of the large-scale azimuthal modes in the vortex ring propagation process. In the experiments, vortex rings are issued from piston-driven axial swirlers with the swirl number ranges from S = 0 to 1.10. The stroke ratio L/D = 1.5 is used to produce a compact vortex ring without a trailing jet. PIV measurements are conducted in a water tank, while the in-plane component flow velocities on the longitudinal center plane and the three-component flow velocities on the cross section plane at several downstream locations according to the ring trajectories are obtained. In the simulation, the axial swirlers are also included, while the piston motion is realized by imposing a time-dependent inflow condition. Two types of dynamic effects in the vortex ring propagation process are captured by the planar-PIV measurement: the arriving time effect and the azimuthal effect, which induce parallel shift of the vortex ring core and the radial tilting of the vortex sheet, respectively. These modes are identified using the stereo-PIV results by applying the fast Fourier transform in the azimuthal direction, followed by the proper orthogonal decomposition on the radial and temporal directions. It shows that both m = 0 and 1 modes (m is the azimuthal wave number) coexist in the weakly swirled vortex rings, while the m = 2 mode arises and the m = 0 mode decays at high swirl numbers. The simulation also identifies the m = 1 and 2 modes, while the m = 2 mode has a large pitch with respect to the formation time.