Abstract
In this study, we consider the oscillatory behavior of mutually impinging jets in an enclosed, dome-shaped mixing chamber. The frequency of the impinging jet oscillations is dictated by the flow rate, with the oscillatory behavior being grouped into three regimes: a low flow rate regime (Re < 1500), a transition regime (1500 < Re < 2000), and a high flow rate regime (Re > 2000). The detailed characteristics of the oscillations in the high flow rate regime (Re = 6800 in the present study) are investigated through simultaneous frequency and refractive-index-matched particle image velocimetry measurements. The oscillation mechanism in the high flow rate regime was found to be similar to that of the other two regimes, where jets collide and interact in an oscillatory manner. However, in the high flow rate regime, there is a distinct and phase-evolving process of saddle point formation and jet bifurcation that is not present at the lower flow rates. The jet bifurcation process is also distinctly related to the balance of vortical structures inside the mixing chamber, and saddle point formation plays a key role in the internal and external flow field of this configuration. The external sweep angle of the exiting jet increases with the flow rate throughout the low and transition flow rate regimes, but a constant sweep angle was found to persist in the high flow rate regime. Thus, formation and location of the internal saddle point is directly linked to the external sweep angle of the jet.
Highlights
Osu.edu investigated the impingement of two identical submerged and opposed water jets at a Re of 1000
The frequency of the impinging jet oscillations is dictated by the flow rate, with the oscillatory behavior being grouped into three regimes: a low flow rate regime (Re < 1500), a transition regime (1500 < Re < 2000), and a high flow rate regime (Re > 2000)
Points A and D show the maximum bifurcated portion for the upper and the lower jets, respectively. These peaks correspond to the phase positions where the saddle points vanish; as mentioned earlier, both jets remain bifurcated for a while due to the energy stored in remnant vorticity from the decayed dome vortex
Summary
Osu.edu investigated the impingement of two identical submerged and opposed water jets at a Re of 1000. The existence of the oscillatory behavior in the mixing chamber that is enclosing impinging opposed jets was reported to be due to the vortices created as a result of the unstable impingement region and pressure feedback from the walls Building on these prior studies, the present work delves into the details of the flow features created as a result of jet impingement in an enclosed dome-shaped chamber by investigating a special fluidic oscillator whose oscillation mechanism relies on mutual impingement of dual jets in an enclosed chamber at a relatively high Re. Fluidic oscillators are a special type of fluidic devices that produce a pulsed or sweeping jet with a wide range of frequencies when supplied by a pressurized fluid. Further details about this experimental setup, the custom microphone-tube sensor configuration, and the quarter-period based technique used to avoid jitters in the PIV phase-averaging process are provided by Tomac and Gregory.
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