The present study investigates the vortex dynamics of the rectangular shaped synthetic jet and reports the occurrence of vortex ring bifurcation along with other reported modes such as axial switching and the vortex suction. The novel finding of vortex ring bifurcation of rectangular synthetic jets has been observed without any other mode of excitation except the periodic axial actuation. The experiments on synthetic jets have been conducted at different actuation frequencies and both qualitative and quantitative characterization of the flow structures has been carried out using Laser Induced Fluorescence (LIF) and Laser Doppler Velocimetry, respectively. LIF flow visualization provides insights into the size of the vortex and the vortex evolution with respect to time, enabling us to propose the flow physics behind the axial switching and the vortex bifurcation processes for rectangular synthetic jets. The proposed flow physics is then quantitatively evidenced by the time-averaged velocity measurements. Vortex splitting or bifurcation is found to occur in the minor axis plane of orifice and the divergence angle depends on the actuation frequency and average velocity of fluid expelled through the orifice in the forward stroke of diaphragm. In the case of occurrence of axial switching, a maximum of three axial switching events are observed before vortex breakup. Finally, by systematically carrying out experiments across a wide range of operational parameters, a narrow region corresponding to the vortex bifurcation has been identified on a Reynolds Number–Strouhal Number map, along with other modes such as axial switching regime and the vortex suction regime. Based on our measurements, a mechanism of vortex bifurcation vis-à-vis axial switching has also been suggested.

本研究调查矩形合成射流的涡流动力学，并报告涡流环分叉的发生以及其他报道的模式，例如轴向切换和涡流吸力。已经观察到矩形合成射流的涡流环分叉的新发现，除了周期性轴向驱动之外，没有任何其他激励模式。合成射流的实验已在不同的驱动频率下进行，并且分别使用激光诱导荧光（LIF）和激光多普勒测速仪对流动结构进行了定性和定量表征。LIF流动可视化提供了关于涡流大小和涡流随时间变化的见解，使我们能够提出矩形合成射流的轴向转换和涡旋分叉过程背后的流动物理学。然后通过时间平均速度测量来定量地证明所提出的流动物理学。发现在孔的短轴平面中发生涡旋分裂或分叉，并且发散角取决于隔膜的前进冲程中通过孔排出的流体的致动频率和平均速度。在发生轴向切换的情况下，在涡旋破裂之前最多观察到三个轴向切换事件。最后，通过在广泛的运行参数范围内系统地进行实验，在涡旋分叉器上已确定了一个与旋涡分叉相对应的狭窄区域。然后通过时间平均速度测量来定量地证明所提出的流动物理学。发现在孔的短轴平面中发生涡旋分裂或分叉，并且发散角取决于隔膜的前进冲程中通过孔排出的流体的致动频率和平均速度。在发生轴向切换的情况下，在涡旋破裂之前最多观察到三个轴向切换事件。最后，通过在广泛的运行参数范围内系统地进行实验，已经确定了对应于涡旋分叉的狭窄区域。然后通过时间平均速度测量来定量地证明所提出的流动物理学。发现在孔的短轴平面中发生涡旋分裂或分叉，并且发散角取决于隔膜的前进冲程中通过孔排出的流体的致动频率和平均速度。在发生轴向切换的情况下，在涡旋破裂之前最多观察到三个轴向切换事件。最后，通过在广泛的运行参数范围内系统地进行实验，已经确定了对应于涡旋分叉的狭窄区域。发现在孔的短轴平面中发生涡旋分裂或分叉，并且发散角取决于隔膜的前进冲程中通过孔排出的流体的致动频率和平均速度。在发生轴向切换的情况下，在涡旋破裂之前最多观察到三个轴向切换事件。最后，通过在广泛的运行参数范围内系统地进行实验，已经确定了对应于涡旋分叉的狭窄区域。发现在孔的短轴平面中发生涡旋分裂或分叉，并且发散角取决于隔膜的前进冲程中通过孔排出的流体的致动频率和平均速度。在发生轴向切换的情况下，在涡旋破裂之前最多观察到三个轴向切换事件。最后，通过在广泛的运行参数范围内系统地进行实验，已经确定了对应于涡旋分叉的狭窄区域。雷诺数– Strouhal数图，以及其他模式，例如轴向切换状态和涡流吸入状态。根据我们的测量结果，还提出了涡旋分叉相对于轴向转换的机制。