Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session GQ: Jet Stability I |
Hide Abstracts |
Chair: Gregory Blaisdell, Purdue University Room: Hilton Chicago Stevens 2 |
Monday, November 21, 2005 10:34AM - 10:47AM |
GQ.00001: Spatial stability analysis of a liquid jet J. Enrique Portillo, Gregory Blaisdell A spatial linear stability analysis of a liquid jet with a locally parallel base flow assumption is performed. It is found that a pocket of absolute instability is present in the region closest to the jet exit and, as suggested by Koch,\footnote{W. Koch, J. Sound and Vibration, 99, 53, 1985.} the most unstable mode occurs at the transition location between the absolutely and convectively unstable regions of the flow. Comparison with experimental results had previously employed the assumption that the wave velocity is close to the jet velocity. However, the obtained eigenvalues suggest a much smaller wave velocity ($\sim 0.5 U_{jet}$). This discrepancy is resolved by performing a Doppler shift analysis on the flow, which takes into account the change in velocity at the jet surface. It is shown that the predicted eigenvalues are in good agreement with the measured wavelength. The validity of the parallel base flow assumption and the effects of weak and strong non-parallelism of the flow are further discussed. [Preview Abstract] |
Monday, November 21, 2005 10:47AM - 11:00AM |
GQ.00002: Atomization of a High Speed Jet Zhiliang Xu, Myoungnyoun Kim, Wonho Oh, James Glimm, Roman Samulyak, Xiaolin Li, Constantine Tzanos We present a numerical study of the jet breakup and spray formation in a diesel engine by the Front Tracking method. The mechanisms of jet breakup and spray formation of a high speed diesel jet injected through a circular nozzle are the key to design a fuel efficient, nonpolluting diesel engine. Many parameters such as the nuzzle shape, the velocity and the turbulence of the jet and the thermodynamic states of liquid and gas could be contributing causes for jet breakup. We conduct the simulations for the jet breakup within a 2D axis-symmetric geometry. Our goal is to model the spray at a micro-physical level, with the creation of individual droplets. The problem is multiscale. The droplets are a few microns in size. The nozzle is about 0.2 mm in diameter and 1 mm in length. In order to resolve various physical patterns such as vortex, shock waves, vacuum and track droplets and spray, the Burger-Colella adaptive mesh refinement technique is used. We model mixed vapor-liquid region through a heterogeneous model with dynamic vapor bubble insertion. On the liquid/vapor interface, a phase transition problem is solved numerically. [Preview Abstract] |
Monday, November 21, 2005 11:00AM - 11:13AM |
GQ.00003: Structure and stability of a round jet exiting a rotating pipe at moderate Reynolds numbers C. del Pino, J. Ortega-Casanova, R. Fernandez-Feria, E. Sanmiguel-Rojas The three-dimensional (3D) structure of a jet of water coming out of a rotating circular pipe into a quiescent tank of water is analyzed both experimentally (through LDA and PIV techniques), and numerically, for several values of the Reynolds number ($Re$) of the order of a few hundreds, and for several values of the swirl parameter ($L$). The observed 3D structure are discussed in the light of a spatial stability analysis of the corresponding axisymmetric jet for the same values of $Re$ and $L$. Good agreement between the experimental measurements and the 3D numerical simulations, and between these and the structures predicted by the stability analysis for the most unstable waves, is found. Helical travelling waves with azimuthal wave number $|n|=1$ are the first to be detected in the swirless jet as $Re$ is increased, and in the swirling jet for a given $Re$ as $L$ is increased. [Preview Abstract] |
Monday, November 21, 2005 11:13AM - 11:26AM |
GQ.00004: Measurement of the Mean Droplet Size in Horizontal, Isothermal Air--Water and Air--Viscous Liquid Free Jets in Quiescent Ambient S. Al-Rabadi, A. Al-Salaymeh, L. Friedel In a free jet where higher turbulence intensity than that of the ambient exists, the liquid phase fragmentation enhanced by aerodynamic forces that are associated with the co-flowed and entrained air is pronounced. Measurements using 2-D PDA as well as high-speed cinematography of air--water and air--viscous liquid in free jets at several nozzle exit pressures and nozzle outlet diameters have been conducted. It became evident that the mean droplet size decreases with increasing air--liquid phase mass flow ratio due to the increase of the shearing on the liquid phase. This leads to substantial liquid fragmentation (primary breakup) and, subsequently, to the formation of satellite droplets with small sizes. This trend becomes significant with increasing liquid viscosity. Higher liquid viscosity than that of water affects the droplet formation and breakup by reducing the rates of surface perturbations and consequently droplet distortions. The droplet velocity decreases with the downstream distance due to the continued air entrainment. The kinetic energy of the droplets is mostly dissipated during the collisions, which may induce further liquid fragmentation and hence formation of a number of relatively smaller droplets (secondary breakup), or the formation of comparatively larger liquid fragments that may rain out the free jet. [Preview Abstract] |
Monday, November 21, 2005 11:26AM - 11:39AM |
GQ.00005: Jet Interaction Studies in a Fluidic Oscillator James Gregory, John Sullivan, Surya Raghu The fluidic oscillator evaluated in this study operates on the interaction of two colliding jets in a two-dimensional mixing chamber. The jet interaction forms an internal oscillating shear layer driven by oscillatory growth of counter-rotating vortices, producing an external oscillating jet at frequencies on the order of kilohertz. Experimental studies involved pressure transducer measurements and flow visualization with pressure-sensitive paint. The effects of various geometrical and gas species configurations were evaluated. Inlet geometry, device scaling, aspect ratio, and supply gas were all varied. These studies reveal that three-dimensional jet interaction becomes dominant for large devices or for high aspect-ratio devices. Mode-hopping behavior was also observed at low flow rates, and was dependent upon inlet geometry. [Preview Abstract] |
Monday, November 21, 2005 11:39AM - 11:52AM |
GQ.00006: Interaction of a Free Turbulent Jet with a Synthetic Jet David Tamburello, Michael Amitay The mechanisms associated with active control of a turbulent radial free jet were investigated experimentally using PIV. The interaction of the main jet with a synthetic jet, driven at a frequency which corresponds to a main jet Strouhal number of 0.16, was explored and compared to the effects of a steady control jet at the same momentum coefficients. Unlike the steady control jet, which mainly vectors the main jet, thus affecting the mean and fluctuating velocity fields, the synthetic jet yields both vectoring of the main jet and its spreading in all directions. At low momentum coefficients, the main jet is slightly vectored away from the synthetic jet, where the additional energy to the coherent structures is the dominant mode of augmentation. At high momentum coefficients, the synthetic jet penetrates through the main jet flow, resulting in a significant modification of the flow field by vectoring the jet much farther than at lower momentum coefficients and enhancing spreading via high added energy to the main jet at selective modes. [Preview Abstract] |
Monday, November 21, 2005 11:52AM - 12:05PM |
GQ.00007: Spanwise Structures in a 2-D Synthetic Jet Florine Cannelle, Michael Amitay A two dimensional isolated zero net mass flux jet, or synthetic jet, was investigated experimentally using Particle Image Velocimetry (PIV) and hot-wire anemometry. The evolution of counter-rotating spanwise coherent structures was explored for different jet orifice aspect ratios. Two synthetic jet configurations were tested, both driven by piezo-ceramic disks, for actuation frequencies of 300 and 917Hz, with various length- and time-scales, Reynolds numbers and several stroke lengths (between 5 to 50 times the slit width). The velocity and vorticity fields were measured in planes along and across the slit. Analysis of the spanwise extent of the jet demonstrates a unique flow pattern, where the flow near the jet exit plane is initially two-dimensional, while farther downstream the vortex pair lines develop secondary counter-rotating streamwise structures, where the streamwise and spanwise spacing between them vary with stroke length and formation frequency. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700