An experimental study is conducted to examine the impact of internal geometry of a fluidic oscillator on its working mechanisms, i.e., the widths of the inlet wedge W1, mixing chamber W2, and exit throat W3, normalized by the width of the inlet throat W0. Using time-resolved particle image velocimetry, the flow dynamics both inside and outside the oscillator are measured simultaneously. The phase-averaged flow fields are obtained using proper orthogonal decomposition analysis based on which the pressure fields are computed. It is found that the external jet spreading angle and the oscillation frequency are proportional to the width of the inlet wedge up to W1/W0 = 2. This is because the inlet wedge controls the feedback flow and accordingly the recirculation bubble in the mixing chamber. At a critical lower value of W1/W0 = 0.8, there is no feedback flow with a stable external sweeping jet. The mixing chamber width W2/W0 controls the size of the recirculation bubble, which has a notable proportional control on the spreading angle. With a small mixing chamber of W2/W0 = 2.9, it is also found that the strong feedback flow can still produce a stable sweeping jet motion but with a small spreading angle. The exit throat width W3/W0 has non-monotonous control on the external jet spreading angle and the oscillation frequency. It is noteworthy that the jet can still produce a stable sweeping motion even with a large value of W3/W0 = 4.2, which can significantly reduce the blocking effect of the exit.

No abstract