On the Stable-Oscillation Domain of a Simple Fluidic Oscillator

Abstract

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.

Two-dimensional analysis of a simplified fluidic oscillator

“…So, this phenomenon can be widely utilised as a simplified fluidic oscillator with non-complicated geometry. Specifically speaking, we have revealed the occurrence conditions for stable jet's oscillation (Hirata et al, 2009), and the effects of a kinetic parameter the Reynolds number Re and of various geometric parameters upon the dominant frequency f D of jet's oscillation (Hirata et al, 2011). This phenomenon is related with neither the edge-tone instability nor the Kármán-vortex-street instability.…”

“…Moreover, Re is fixed to 500 in all the computations, being approximated to be large enough. This is because we can ignore the Re effects upon both St and the occurrence condition for Re > 200 (see Hirata et al, 2009) Hirata et al, 2009). Specifically speaking, a/b and B/b are fixed to 2.5 and 15, respectively.…”

“…A few exceptions with non-complicated geometries are a two-dimensional one reported by Yamasaki et al (1988), Hirata et al (2009Hirata et al ( & 2011 and three-dimensional ones reported by Shakouchi (1989) and Mi et al (2001). -We should note that these three-dimensional ones seem to be two-dimensional owing to their flapping motions, but three-dimensional flow is necessary for oscillation.…”

“…And because, the existence of two confining sidewalls is necessary. Actually, stable oscillation is suppressed at B/d ≥ 4 (Hirata et al, 2009). -We should note that, in some cases, a confined jet could suppress its self-excited oscillation in contrast (see Haneda et al, 1995).-However, our knowledge is not enough to understand the oscillation mechanism of the phenomenon.…”

“…This phenomenon is related with neither the edge-tone instability nor the Kármán-vortex-street instability. Because, jet-oscillation frequency is much smaller than those of such instabilities (Hirata et al, 2009(Hirata et al, & 2011. And because, the existence of two confining sidewalls is necessary.…”