Two-dimensional time-resolved particle image velocimetry (TR-PIV) measurements were carried out in confined and non-confined channels with a backward facing step (BFS) while the inlet flow was an oscillating jet from a double feedback fluidic oscillator. In addition, different Reynolds (Re) numbers in the range of 2500–10,000 were applied (based on the hydraulic diameter and mean velocity of jet throat) and the velocity distribution of the oscillating jet was measured in external domains. The effects of the aspect ratio (AR) of the expanded region and the expansion ratio (ER) were studied. Typical time-averaged structures of velocity statistics and the Proper Orthogonal Decomposition (POD) method were used to analyze the flow dynamics. The results show that the oscillation frequency is independent of the external domain and is almost constant for different ER or AR. In contrast, the spreading angle of the fluidic oscillator is much larger value when increasing Re number or decreasing AR. Additionally, a pair of vortices is induced because of the entrainment effect in confined external domain, and the velocity fluctuations can also be increased. Furthermore, the POD analysis revealed that the first two modes are predominant and represent the main characteristics of the flow.

二维时间分辨粒子图像测速（TR-PIV）测量是在密闭通道和非密闭通道中进行的，并具有向后的台阶（BFS），而入口流是来自双反馈流体振荡器的振荡射流。另外，应用了在2500–10,000范围内的不同雷诺数（Re）（基于水力直径和射流喉的平均速度），并且在外部域中测量了振荡射流的速度分布。研究了扩展区域的纵横比（AR）和扩展比（ER）的影响。使用典型的时间平均速度统计结构和适当的正交分解（POD）方法来分析流动动力学。结果表明，振荡频率与外部域无关，并且对于不同的ER或AR几乎是恒定的。相反，当增加Re数或减小AR时，流体振荡器的扩展角大得多。另外，由于在有限的外部区域中的夹带效应而引起一对涡流，并且速度波动也可以增加。此外，POD分析显示前两种模式占主导地位，代表了流量的主要特征。