A confined jet sometimes causes a self-exited oscillation due to the existence of a downstream target. In this work, the authors study this phenomenon. More specifically, the authors deal with a simple fluidic oscillator; namely, a two-dimensional confined jet into an abruptly-expanding channel with a downstream target of a square cylinder. The authors conduct the velocity measurements by an UVP (ultrasonic velocity profiler). Besides, the flow patterns in the fluidic oscillator are observed by a PIV (particle image velocimetry). As a result, the authors reveal the geometrical effects upon the range of stable jet's oscillation, such as the aspect-ratio effect, the channel-breadth effect, the cylinder-size effect and the cylinder-distance effect, together with the Re effect.

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A confined jet sometimes causes self-exited oscillations due to an existence of a downstream obstacle.This phenomenon is useful for fluidic oscillators, heat/material mixers and flowmeters, in order to realise a low-cost high-reliability device without mechanically moving components. In the present study, the authors deal with this phenomenon at low Reynolds numbers (Re=500), experimentally. More specifically, the autors conduct a time series of flow visualisations and PIV(Particle Image Verocimatry) analyses, with the measurement by UVP for accuracy check. As a result, the autors propose a new definition of length scale of vertical structures and propose a formula to predict the oscillation frequency using the length scale.