Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session H36: Jets II |
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Chair: Leonardo Chamorro, University of Illinois at Urbana-Champaign Room: Alcove A |
Monday, November 24, 2014 10:30AM - 10:43AM |
H36.00001: Bouncing and Merging of Liquid Jets Abhishek Saha, Minglei Li, Chung K. Law Collision of two fluid jets is a technique that is utilized in many industrial applications, such as in rocket engines, to achieve controlled mixing, atomization and sometimes liquid phase reactions. Thus, the dynamics of colliding jets have direct impact on the performance, efficiency and reliability of such applications. In analogy with the dynamics of droplet-droplet collision, in this work we have experimentally demonstrated, for $n$-alkane hydrocarbons as well as water, that with increasing impact inertia obliquely colliding jets also exhibit the same nonmonotonic responses of merging, bouncing, merging again, and merging followed by disintegration; and that the continuous entrainment of the boundary layer air over the jet surface into the colliding interfacial region leads to two distinguishing features of jet collision, namely: there exists a maximum impact angle beyond which merging is always possible, and that merging is inhibited and then promoted with increasing pressure. These distinct response regimes were mapped and explained on the bases of impact inertia, deformation of the jet surface, viscous loss within the jet interior, and the thickness and pressure build-up within the interfacial region in order to activate the attractive surface van der Waals force to effect merging. [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H36.00002: The Dynamics of Coherent Structures in Under-expanded Supersonic Impinging Jets Paul Stegeman, Andrew Ooi, Julio Soria This study looks at the spatio-temporal dynamics of the coherent structures found in under-expanded supersonic impinging jets from a circular nozzle at a pressure ratio of $3.4$ and standoff distances of $\left\{1d,2d,3d\right\}$. In these jets the development of coherent structures within the shear layer and their interaction with a standoff-shock are the principle components of a fundamental non-linear acoustic feedback mechanism. Temporally resolved and phase averaged data for each case was generated from a three dimensional hybrid large-eddy simulation on a non-uniform structured cylindrical grid with computational domains consisting of approximately $8.6$, $10.6$ and $12.8$ million nodes for each of the cases respectively. From these datasets we investigate the development of the energy distribution and topology of the coherent structures as a function of their distance traveled along the shear-layer from their initial growth period to their interaction with the standoff-shock wave. Furthering this analysis the various terms in the kinetic and internal energy transport equations are examined to gain insight into the physical mechanisms for the transfer of energy to/from the coherent structures. [Preview Abstract] |
Monday, November 24, 2014 10:56AM - 11:09AM |
H36.00003: Flow field features of impinging jets with fractal grids Gioacchino Cafiero, Stefano Discetti, Tommaso Astarita An experimental investigation of the flow field features of impinging jets equipped with a fractal turbulence promoter at short nozzle to plate distances is carried out by means of 2D-3C Particle Image Velocimetry (Stereo-PIV). The test Reynolds number based on the nozzle diameter is set to 10,000. Both the instantaneous and the time averaged features of such flow field are discussed. The comparison with the well-known features of a circular jet without any turbulator (JWT) reveals how some of the peculiar features of this flow field are suppressed by the presence of the grid. The typical ring-vortex that arises as a consequence of the shear layer instability is perturbed and suppressed by the high frequency disturbance introduced by the grid. As a consequence, there is no vortex separation in correspondence of the impinging plate, then leading to the absence of the characteristic ``double peak'' in the Nusselt number profile for JWT. [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H36.00004: Experimental studies on circular and AR4 elliptic vortex-ring impingement upon inclined surfaces Shengxian Shi, Tze How New, Jian Chen PLIF flow visualisation and TR-PIV measurements were performed on the impingement of circular and AR4 elliptic vortex-rings upon flat surface with different inclination angles at Re$=$4000. This is aimed to investigate the effects of nozzle geometry, surface inclination angle and exit-surface separation distance on the vortex-ring impingement behaviour. Separation distance between nozzle exit and flat surface were adjusted for the elliptic vortex-ring so as to examine the flow structures for impingement prior, at and posterior the axis-switching point. Current results on circular vortex-ring show that at low inclination angle, vortex-ring underwent severe stretching during the impingement and vortex-ring core closer to the flat surface was observed to induce secondary vortex-ring and pair with it before its pinch-off. Meanwhile, vortex-ring core further away from the flat surface produced secondary and tertiary vortex-rings before transit into turbulence. At high inclination angles, vortex-ring core closer to the flat surface was quickly entrained by the primary vortex-ring after the impingement. Experiments on elliptic vortex-ring are undergoing at the moment, more findings will be presented in the conference. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H36.00005: Experimental investigation of a confined developing axisymmetric wall jet Tianqi Guo, Matthew Rau, Pavlos Vlachos, Suresh Garimella The present work reports an experimental study of an axisymmetric, confined wall jet using planar particle image velocimetry (PIV) and the dielectric liquid HFE-7100. The wall jet is formed downstream from a confined and submerged impinging round jet, 3.75 mm in diameter. Both the developing region and self-similar region of the wall jet are investigated. The experiments are conducted for Reynolds numbers (Re $=$ Ud/$\upsilon )$ ranging from 1500 to 38000 and at a nozzle-to-plate spacing of four jet diameters. Image-preprocessing techniques are used to eliminate background noise and an ensemble correlation scheme is applied to improve the resolution of the measurement of the mean velocity field near the wall. A maximum measurement resolution of 36 $\mu $m is achieved. Profiles of the mean velocity, turbulent intensities, decay rate, spread rate and wall shear stress are used to characterize the influence of confinement on the wall jet development and inner layer scaling. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H36.00006: Jet Velocity Profile Effects on Spray Characteristics of Impinging Jets at High Reynolds and Weber Numbers Neil S. Rodrigues, Varun Kulkarni, Paul E. Sojka While like-on-like doublet impinging jet atomization has been extensively studied in the literature, there is poor agreement between experimentally observed spray characteristics and theoretical predictions (Ryan et al. 1995, Anderson et al. 2006). Recent works (Bremond and Villermaux 2006, Choo and Kang 2007) have introduced a non-uniform jet velocity profile, which lead to a deviation from the standard assumptions for the sheet velocity and the sheet thickness parameter. These works have assumed a parabolic profile to serve as another limit to the traditional uniform jet velocity profile assumption. Incorporating a non-uniform jet velocity profile results in the sheet velocity and the sheet thickness parameter depending on the sheet azimuthal angle. In this work, the 1/7$^{\mathrm{th}}$ power-law turbulent velocity profile is assumed to provide a closer match to the flow behavior of jets at high Reynolds and Weber numbers, which correspond to the impact wave regime. Predictions for the maximum wavelength, sheet breakup length, ligament diameter, and drop diameter are compared with experimental observations. The results demonstrate better agreement between experimentally measured values and predictions, compared to previous models. [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H36.00007: Mixing Characteristics for Flush and Elevated Jets in Crossflow Levon Gevorkyan, Takeshi Shoji, Wen Yu Peng, Daniel Getsinger, Owen Smith, Ann Karagozian The present experiments explore the mixing and structural characteristics of equidensity and variable density gas-phase transverse jets using acetone PLIF as well as stereo PIV. Flush and elevated nozzles as well as a flush pipe geometry are explored in these studies, for a range of jet-to-crossflow momentum flux ratios $J$ and density ratios $S$, spanning previously-determined conditions creating upstream shear layers which are either convectively unstable or absolutely unstable. The present studies quantify a range of mixing and flow metrics for the jet in crossflow, including conditional unmixedness, conditional probability density function, and scalar dissipation rates associated with both the jet cross-section and the centerplane longitudinal imaging. Correlations between mixing parameters and the structural symmetry/asymmetry in the JICF are observed, as are connections with the state of the shear layer and vorticity evolution. [Preview Abstract] |
Monday, November 24, 2014 12:01PM - 12:14PM |
H36.00008: Pressure Modulated Sonic Jet in Supersonic Crossflow Tobias Rossmann Sonic transverse jets in supersonic crossflow are modulated using high-amplitude variations in jet stagnation pressure to enhance jet penetration and mixing. An injection/modulation apparatus combining a powered resonance tube and acoustic resonator is used to create low momentum ratio jets ($J = 1, 2$) in a supersonic cross-stream ($M = 3.5$). The injector has the capability to modulate the jet supply pressure at sufficiently high frequency ( $> 15$ kHz) and amplitude (up to 190 dB) to access relevant Strouhal numbers ($St = 0 - 0.3$) and amplitudes (up to 10\% of the jet stagnation pressure) related to mixing enhancement. Planar laser Mie scattering in both side and end views allows for instantaneous imaging of the jet fluid to quantify jet trajectory, spread, and mixing behavior. For modulated $J = 2$ transverse jets, the recirculation zone directly downstream of the injection location is eliminated and significantly faster centerline signal decay rates are seen. For the $J = 1$ modulated jets, substantial increases in centerline penetration, jet spread, and centerline signal decay rate are shown. Additionally, PDF analysis of the instantaneous jet fluid signal values is performed to compare local mixing efficiencies between the modulated and un-modulated cases. [Preview Abstract] |
Monday, November 24, 2014 12:14PM - 12:27PM |
H36.00009: Rapid 3D Printing of Multifunctional Calcium Alginate Gel Pipes using Coaxial Jet Extruder Konrad Rykaczewski, Viraj Damle Calcium alginate (CA) forms when solution containing sodium alginate (SA) comes in contact with a CaCl2 solution. The resulting gel is biocompatible as well as edible and is used in production of bio-scaffolds, artificial plant seeds, and edible substances. In the latter application, referred to in the culinary world as ``spherification,'' flavored liquids are mixed with the SA and dripped into CaCl2 solution to form gel encapsulated flavored ``marbles.'' Previously, crude 3D printing of CA structures has been achieved by stacking of such flavored liquid filled marbles [1]. In turn, solid CA rods have been fabricated by properly mixing flow of the two solutions using a microfluidic device [2]. Here we show that by using two circular cross-section coaxial nozzles to produce coaxial jets of the SA and CaCl2 solutions, liquid filled CA micro-to-mili scale gel pipes can be produced at speeds around $\sim$ 150 mm/s. Such extrusion rate is compatible with most commercially available 3D printers, facilitating adoption of the CA pipe coaxial jet extruder. Here, the impact of inner and outer liquid properties and flow speeds on the gel pipe extrusion process is discussed.\\[4pt] [1] www.dovetailed.co\\[0pt] [2] Beyer et al. Solid-State Sens., Act.nMicrosys. 2013, 1206-1209. [Preview Abstract] |
Monday, November 24, 2014 12:27PM - 12:40PM |
H36.00010: Simulation of direct contact condensation of steam jets based on interfacial instability theories David Heinze, Thomas Schulenberg, Andreas Class, Lars Behnke A simulation model\footnote{Heinze et al. A Physically Based, One-Dimensional Simulation Model of Direct Contact Condensation of Steam Jets, submitted to ASME Journal of Nuclear Engineering} for the direct contact condensation of steam in subcooled water is presented that allows to determine major parameters of the process such as the jet penetration length. Entrainment of water by the steam jet is modeled based on the Kelvin-Helmholtz and Rayleigh-Taylor instability theories. Primary atomization due to acceleration of interfacial waves and secondary atomization due to aerodynamic forces account for the initial size of entrained droplets. The resulting steam-water two-phase flow is simulated based on a one-dimensional two-fluid model. An interfacial area transport equation is used to track changes of the interfacial area density due to droplet entrainment and steam condensation. Interfacial heat and mass transfer rates during condensation are calculated using the two-resistance model. The resulting two-phase flow equations constitute a system of ordinary differential equations which is discretized by means of an explicit Runge-Kutta method. The simulation results are in good agreement with published experimental data over a wide range of pool temperatures and mass flow rates. [Preview Abstract] |
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