Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session G15: Jets: General |
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Chair: Kathy Prestridge, Los Alamos National Laboratory Room: 310 |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G15.00001: How is the eigenframe of the rate-of-strain tensor perturbed by density gradients? Dominique Fratantonio, Chris Lai, John Charonko, Kathy Prestridge We present an experimental study on a variable-density turbulent jet. The jet's three-dimensional density and velocity fields have been reconstructed using a time-resolved simultaneous stereoscopic PIV and planar LIF system together with the \textit{Taylor's frozen turbulence hypothesis. }The obtained dataset is then analyzed to understand how density gradients perturb the eigenframe of the rate-of-strain tensor whose alignments with the vorticity vector govern the key turbulence process of vortex-stretching. [Preview Abstract] |
Sunday, November 24, 2019 4:01PM - 4:14PM |
G15.00002: Air entrainment by 2D plunging jets Nicole Farias, Simo A. Mäkiharju Air entrainment from liquid plunging jets are commonly found in nature and industry applications. As a result, this phenomenon has been the focus of many studies in the past, which showed it to have a significant contribution to the energy and mass transfer between gas and liquids. Air entrapment was also discovered to be a function of various parameters, such as jet impact velocity, geometry, fluid properties, and resulting jet instabilities. Due to the complex multiphase flow involved, no exhaustive characterization or theory is yet available, and limited data has been published on the dynamics within the entrainment zone once entrainment becomes significant enough to make the flow optically opaque. We study 2D plunging jets using high-speed video, point probes and O(10kHz) 2D X-ray densitometry to examine the air entrainment and nominally 2D flow structures, while varying jet size, speed, height and angle, and fluid properties such as surface tension and viscosity. We span Reynolds numbers from 7 to 25 x10$^{\mathrm{3}}$, and Weber numbers from 0.3 to 40.4. The high-speed x-ray densitometry we employ enables time-resolved analysis of phase fraction in large areas with greater efficiency and detail than feasible utilizing point probes alone. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G15.00003: The combined effect of internal and external intermittency in turbulent jet flows Michael Gauding, Yacine Brahami, Luminita Danaila, Emilien Varea The combined effect of internal and external intermittency on the statistical properties of small-scale turbulence is investigated in a temporally evolving, planar turbulent jet flow. In turbulent jet flows, the phenomenon of external intermittency originates from a very thin layer, known as turbulent/non-turbulent interface, that separates the inner turbulent core from the outer irrotational surrounding fluid. The impact of external intermittency on small-scale turbulence is studied across the jet by the self-similarity solution of higher-order structure functions. It is shown that the scaling of structure functions exhibits a growing departure from the prediction of classical scaling solutions toward the edge. Empirical evidence is provided that this departure is primarily due to external intermittency and the associated break-down of self-similarity. By conditioning structure functions on an external intermittency parameter, it is shown that the self-similarity solution of structure functions can be recovered. The analysis is based on highly resolved direct numerical simulations. [Preview Abstract] |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G15.00004: Structure of two-dimensional turbulent wall jets Shivsai Dixit, Harish Choudhary, Abhishek Gupta, Thara Prabhakaran, Abhay Kumar Singh Two-dimensional turbulent wall jets find important applications in engineering and meteorology, and present unique features such the non-monotone mean velocity profile, a region of counter-gradient momentum diffusion etc. that are very different from other canonical turbulent wall-bounded flows. We propose that the wall-jet flow structure consists of universal full free-jet outer flow and wall-scaled inner flow. We further argue that there exists strong, nonlinear inner-outer interaction which could lead to the Reynolds number dependence of the overlap layer in wall jets. We present experimental hotwire and PIV data from our wall jet setup, over a range of Reynolds numbers, to substantiate this view. Further, an overlap analysis of the mean velocity profile shows that the Reynolds-number-dependence of the overlap layer can be effectively absorbed into an intermediate coordinate leading to universal overlap description in terms of the intermediate variable. Spectra and correlation maps also show promising support for the proposed structure of wall jets. [Preview Abstract] |
Sunday, November 24, 2019 4:40PM - 4:53PM |
G15.00005: Optical measurement of the interaction between outwardly oriented, steady gas jets Frank Austin Mier, Simone Hill, Michael Hargather Nearby gas jets issuing into a quiescent environment interact with each other in various manners dependent on their relative spacing and orientation. While the study of a single turbulent jet is classical to fluid dynamics, and entrainment between parallel jets at varying spacing has been quantified, this investigation aims to determine how an outward projection will affect the jet interaction. Here, Particle Image Velocimetry (PIV) and high-speed schlieren imaging are performed to characterize this interaction. An experiment was designed to produce steady gas venting through custom orifice plates at a range of choked and un-choked stagnation pressures. Orifice plates produced jets offset at incremented angles from 0$^\circ$ to 60$^\circ$. Downstream jet interactions are analyzed through the measured PIV velocity field and flow feature observations from high-speed schlieren images. The velocity profile findings are compared to the well-defined parallel jet case. This work provides a fundamental understanding of the flow structure and velocity field of outwardly directed jets with broad potential application, including the external fluid-dynamics of lithium ion battery venting failures. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G15.00006: Bifurcating jet in transvere acoustic field Eirik Asoy, Jose G. Aguilar, Nicholas A. Worth, James R. Dawson The far-field of an axisymmetric round jet is usually characterized by the momentum flux at the nozzle exit. However, it has been shown that when the jet is submitted to external forcing, the far-field exhibits different behavior from a classical jet. We present experiments of an axisymmetric jet subjected to external forcing by placing the nozzle exit in a standing acoustic field by forcing a rectangular box with loud-speakers. Several forcing conditions at the nozzle exit, i.e different combinations of transverse and longitudinal velocity oscillations, are achieved by placing the nozzle at different positions relative to the pressure node. Time-resolved Particle Image Velocimetry (PIV) combined with microphone measurements are used to characterize the flow field in a plane of interest and the acoustic fields. It is found that the jet bifurcates, i.e splits into two or three separate momentum streams, at sufficiently high forcing levels when placed anywhere else than at a pressure anti-node. Furthermore, the flow field is asymmetric at any position between the pressure and velocity nodes. This asymmetry is symmetric across the pressure anti node which is shown to be linked to the relative phase between transverse and longitudinal velocity oscillations. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G15.00007: Reevaluating the jet breakup regime diagram Ben Trettel Identifying the regime of a liquid jet is necessary to determine the physical mechanisms causing breakup and consequently how to model the jet. Existing regime diagrams are based on a small amount of data classified by superficial visual characteristics, making these diagrams too inaccurate to reliably determine the correct regime. A more accurate regime diagram is developed using a large compilation of breakup length data combined with theory where the data is sparse. Improvements in the regime diagram include a new regime, the addition of the nozzle critical Reynolds number and the turbulence intensity as variables, and the recognition that how the regimes change with increasing velocity (i.e., Rayleigh to first wind-induced to second wind-induced to atomization) is not universal. [Preview Abstract] |
Sunday, November 24, 2019 5:19PM - 5:32PM |
G15.00008: Droplet size distribution along the near-field interface of immiscible turbulent jets Eric Ibarra, Franklin Shaffer, Omer Savas This work examines the droplet distributions of submerged, immiscible, turbulent jets in the near field. Experiments consists of silicone oil jets of two viscosities submerged in a water tank. The jet Reynolds numbers are in the range of $Re \sim 3,500 - 27,000$. Shadowgraphy is used to investigate the droplet sizes at the edge of the jets which are quantified using Hough transformation. The droplet size distributions are observed to be bi-modal. The form of these distributions draw attention to prevalence of observed small satellite droplets being formed from the rupture of sheared ligaments in the flow. Results suggest that the radii of the small satellite droplets are independent of $Re$, while the average size of the large droplets is governed by the Weber number. High speed videos showing droplet shearing from large, submerged hydrocarbon jets into seawater will be presented. [Preview Abstract] |
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