Browsing by Author "Tomac, Mehmet N."

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Effect of Geometry Modifications on the Vectoring Performance of a Controlled Jet
(ISFAHAN UNIV TECHNOLOGY, MECHANICAL ENGINEEING DEPT, JAFM OFFICE, ISFAHAN, 84156-83111, IRAN, 2017) Tomac, Mehmet N.; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Tomac, Mehmet N.
Jet vectoring performances of ten different designs with various depths and geometrical outlines were quantified through constant temperature anemometry measurements for a Reynolds number range from 10,000 to 30,000 by using passive and active flow control methods at cold flow. The reference design was based on NASA's double throat nozzle concept and a self-injection double throat nozzle design that uses similar flow control concept as the reference design, were also tested for performance comparison. Furthermore, jet vectoring performance of a single throat design, utilizing Coanda effect for jet vectoring, was also quantified. Results indicated jet vectoring angles starting from 2 degrees up to 47 degrees for a control jet flow rate range from 1% up to 10% with respect to the primary jet flow rate in the investigated Re range. Maximum jet vectoring angle was achieved with a single throat design which incorporates small step geometry before the Coanda surface for more effective flow attachment and these results were compared with the vectoring performance of the double throat nozzle designs.
INTERNAL FLOW PHYSICS OF A FLUIDIC OSCILLATOR SPRAY IN THE TRANSITION REGIME
(BEGELL HOUSE INC50 NORTH ST, DANBURY, CT 06810, 2016) Tomac, Mehmet N.; Gregory, James W.; 0000-0002-8589-8758; 0000-0003-1373-4639; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Tomac, Mehmet N.
An experimental investigation of the underlying flow physics of a dual-jet interaction fluidic oscillator spray has been conducted in the transition regime for a Reynolds number of 1680. The transition regime is defined as a narrow range of flow rates between two other operating modes of the fluidic oscillator. Particle image velocimetry (PIV) was used with refractive index-matching sodium iodide solution to minimize reflections from the spray geometry and obtain detailed internal velocity fields. PIV results show that the interaction of the two internal jets and the resultant vortices are responsible for the oscillation mechanism in the transition regime. Two side vortices sustain their existence throughout the oscillation period by altering their size, shape, and strength, and a dome vortex is created twice each oscillation period (once from each jet). The dome vortex plays a key role in the kinetic energy transfer mechanism inside the oscillator by means of jet bifurcations. The primary oscillation mechanism in the transition regime is that each internal jet's connection with the exiting jet is cut completely by the dome vortex in every period. This is in contrast to the low-flow rate oscillation mechanism, in which the oscillations are created by continuous collisions of the jets. Furthermore, the internal jets are observed to energize the side vortex on the opposite side of the chamber-a phenomenon that was not observed in the low-flow rate regime.
Oscillation characteristics of mutually impinging dual jets in a mixing chamber
(AMER INST PHYSICS, 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA, 2018) Tomac, Mehmet N.; Gregory, James W.; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü;
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).