Abstract
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.
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