Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Article Citation - WoS: 33Citation - Scopus: 35Oscillation Characteristics of Mutually Impinging Dual Jets in a Mixing Chamber(Amer Inst Physics, 2018-11-01) Tomac, Mehmet N.; Gregory, James W.In this study, we consider the oscillatory behavior of mutually impinging jets in an enclosed, domeshaped 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. (C) 2018 Author(s).Article Citation - WoS: 50Citation - Scopus: 61Internal Jet Interactions in a Fluidic Oscillator at Low Flow Rate(Springer, 2014-05) Tomac, Mehmet N.; Gregory, James W.This study focuses on the internal jet interactions and the oscillation mechanism of the feedback-free fluidic oscillator at low flow rate, corresponding to a Reynolds number of 1,350 (based on exit nozzle width and average exit velocity). Particle image velocimetry (PIV) was used in this study with a refractive index-matched fluid to minimize reflections that would otherwise occur at the fluid-acrylic interface in the test setup. A simple microphone-tube sensor configuration generated a reference signal, with a phase-averaging method based on each quarter period for velocity time history reconstruction. PIV results revealed the existence of a vortex of fluctuating size, shape, and strength on each side of the oscillator; and two transient vortices that are formed in the dome region of the oscillator by each of the jets once per period. The dome vortices periodically bifurcate each of the jets and transfer some of the kinetic energy of that jet to the opposing jet. This kinetic energy transfer mechanism dictates the dominance of either jet at the exit, and this mechanism repeats itself to sustain the oscillations created by the fluidic oscillator. At this flow rate, the two jets form a continuous mutual collision, and the jets are never completely cut off from the exit. The oscillatory behavior at this flow rate is due to a complex combination of jet interactions and bifurcations, vortex-shear layer interactions, vortex-wall interactions, and saddle point formations.