Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session J37: Fluid Turbulence and Instabilities |
Hide Abstracts |
Sponsoring Units: DFD GSNP Chair: Guenter Ahlers, University of California-Santa Barbara Room: LACC 512 |
Tuesday, March 22, 2005 11:15AM - 11:27AM |
J37.00001: Concentration and Velocity Structure of Self-Preserving Steady Round Buoyant Turbulent Plumes in Crossflow Francisco J. Diez, Luis P. Bernal, Gerard M. Faeth The structure of self-preserving steady round buoyant turbulent plumes in uniform crossflows were studied. The experiments involved a round salt-containing (sodium phosphate) water source jet injected into an ethyl-alcohol/water crossflow to match the refractive indices of the two flows in a water channel. Planar-Laser-Induced Fluorescence (PLIF) was used to measure mean and rms fluctuating concentrations of source fluid whereas Particle-Image-Velocimetry (PIV) was used to measure mean and rms fluctuating velocities, both over cross-sections of the flow. Self-preserving behavior was reached when the plumes were deflected into nearly the crossflow direction, yielding counter-rotating vortex systems similar to self-preserving line thermals. As a result, achieving self-preservation was strongly affected by the source/crossflow velocity ratio, e.g., the self-preserving region was observed for (x$_{c}$-x$_{os})$/d greater than the following values: 25 (u$_{o}$/v$_{\infty }$=5), 110 (u$_{o}$/v$_{\infty }$=50) and 170 (u$_{o}$/v$_{\infty }$=100). At self-preserving conditions, it was possible to construct contour plots of concentration and velocity properties over the flow cross section using scaled self-preserving variables. Another interesting property of these flows is their surprisingly rapid mixing; this was indicated by a flow width for plumes in crossflows that was 2.7 times larger than that of plumes in still surroundings. [Preview Abstract] |
Tuesday, March 22, 2005 11:27AM - 11:39AM |
J37.00002: Particle-Generated Isotropic Turbulence in the Final-Decay Period Kyungjin Lee, G.M. Faeth, J.-H. Chen Isotropic turbulence generated by uniform fluxes of mono- and poly-disperse particle moving through gases was studied theoretically and experimentally. Measurements involved mean and rms fluctuating velocities, velocity PDF's, energy spectra, and integral and Taylor length scales. Particle-generated turbulence proved to be isotropic turbulence in the final-decay period that had several unusual features compared to conventional isotropic turbulence in the initial-decay period: rates of dissipation of turbulence kinetic energy were enhanced, ratios of integral/Taylor length scales were unusually large, and ratios of integral/Taylor length scales decreased with increasing turbulence Reynolds number, which is just opposite to conventional isotropic turbulence in the initial-decay period. Finally, the properties of the energy spectra of isotropic turbulence in the final-decay period yielded an effective correlation between the rates of turbulence production by the stirring action of the dispersed particles and the relative turbulence intensities of the particle-generated turbulence. [Preview Abstract] |
Tuesday, March 22, 2005 11:39AM - 11:51AM |
J37.00003: Dynamic PIV measurement on the wake of thin plate Koji Okamoto, Masaaki Ishikawa, Hajime Akimoto Dynamic PIV (Particle Image Velocimetry) with high-speed camera and high repetition laser is focused as quantitative measurement of the transient phenomenon. This system is possible to expand to time resolution of high frequency at 1kHz or 10kHz and it can be widely applied as time serial measurement of PIV which has remained the two-dimensional velocityThe configuration of high-speed camera is 512×256 pixels and 10kHz in frame rate. The repetition rate of double pulse laser is 5kHz for each rod. Double pulse interval is 20$\mu$s using frame straddling technique. The wake of the thin plate has been clearly visualized using the Dynamic PIV system. The vortex dynamics of the turbulent boundary layer has been investigated using the velocity data. [Preview Abstract] |
Tuesday, March 22, 2005 11:51AM - 12:03PM |
J37.00004: A Structural-based Interpretation of the Strouhal-Reynolds Number Relationship Pedram Roushan, X.L. Wu We propose a new Strouhal-Reynolds number relationship for shedding of vortices from circular cylinders. This new relationship is motivated by the observations that (i) for a fixed mean velocity U, the vortex street travels at a constant velocity v$_{st}$=cU independent of the rod diameter D, and (ii) the spatial periodicity \textit{$\lambda $} of the street is linearly proportional to D with $\lambda =\lambda _{0}+\alpha $D, where c, $\lambda _{0}$ and $\alpha $ are constants. It follows that the non-dimensional frequency or the Strouhal number St(=fD/U) should scale with the Reynolds number Re as St=1/(A+B/Re), where A and B are functions of $\lambda _{0}$, $\alpha $, and c. For the laminar wake, our result outperforms the classical relation, proposed by Lord Rayleigh, while it is comparable to other postulated relations in terms of accuracy in fitting experimental data. More significantly it describes remarkably well the two-dimensional (2D) film experiments over a broad range of Re (10$<$Re$<$3,000), where vortex shedding is unaffected by 3D instabilities encountered in all 3D measurements. We note that while the new relation converges to the classical result in the limit of a large Re, the 1/Re expansion, required for such a convergence, is not in general valid as originally proposed by Rayleigh. [Preview Abstract] |
Tuesday, March 22, 2005 12:03PM - 12:15PM |
J37.00005: Global modes in forced wakes Benjamin Thiria, Jose Eduardo Wesfreid We are studying the B\'{e}nard-Von Karman instability near the threshold under forcing conditions in the wake of a cylinder performing rotary oscillations around its axis.of the lock-on region, the vortices are shed at the forcing frequency in the near wake and persist on a characteristic length which depends on the forcing conditions. Downstream of this region, the system always selects a different frequency in the far wake, which is close to the natural one.complete study of the linear stability in the case of forced wakes has shown a modification in the nature (magnitude and length) of the absolute instability region typical of synchronised open flows. For frequencies bigger than the unforced one, this absolute-convective instability transition is pushed back as a function of the forcing amplitude downstream of the cylinder. present experiments in order to study the shape of this new global mode. We will show that these different global modes, due to the effect of the forcing, present scaling laws as a function of the intensity and the frequency of the forcing. These scaling laws are presented as a function of the effective growth rate modified by the mean flow perturbation induced by the forcing.is the first time that a full explanation for the behaviour of forced flows is provided and which includes the understanding of the limits of the lock-on regions. [Preview Abstract] |
Tuesday, March 22, 2005 12:15PM - 12:27PM |
J37.00006: Reynolds number measurements in Rayleigh-Benard convection Denis Funfschilling, Eric Brown, Alexei Nikolaenko, Guenter Ahlers We determined the Reynolds number $R_e$ in cylindrical cells of aspect ratio $\Gamma \equiv D/L = 1$ ($D =$ diameter, $L = $ height) filled with water at a mean temperature of 40$^\circ$C and heated from below for Rayleigh numbers $R$ from $10^9$ to $10^{11}$. It is well known that the main flow structure in this system is a collection of hot and cold plumes and an associated large-scale circulation (LSC). We measured the temperature of the cell side-wall as a function of time at eight azimuthal locations on the horizontal mid-plane. The cross-correlation functions of temperatures on opposite sides of the cell indicate that localized hot or cold volumes associated with the LSC survive for a time comparable to the turnover time $\tau$ as they follow the LSC. >From maxima of the cross-correlation functions we find $\tau$, and from it the Reynolds number $R_e \equiv (4L/\tau)(L/\nu)$ ($\nu$ is the kinematic viscosity), of the LSC. The results are consistent with measurements by others \footnote{X.-L. Qiu and P. Tong, Phys. Rev. E {\bf 66}, 026308 (2002).} for $R \alt 10^ {10}$ and with the prediction of Grossmann and Lohse footnote{S. Grossmann and D. Lohse, Phys. Rev. E {\bf 66}, 016305 (2002).}. [Preview Abstract] |
Tuesday, March 22, 2005 12:27PM - 12:39PM |
J37.00007: Plume Dynamics in Two-Dimensional Thermal Convection Jie Zhang, Yonggun Jun, Xiaolun Wu We investigated single-point velocity statistics of convective turbulence driven by a thermal gradient in a freely suspended soap film in the plume dominant regime in the absence of the large scale circulation. The velocity probability density function (pdf) measured at the center of the convective region is strongly non-Gaussian and is asymmetric along the vertical direction. For positive fluctuations (velocity against gravity), the pdf tail is close to an exponential form with P(v$_{y})\sim $exp(-v$_{y}$/v$_{yrms})$ whereas for negative fluctuations (velocity parallel to gravity), the pdf is super-Gaussian with P(v$_{y})\sim $exp(-$\vert $v$_{y}$/v$_{yrms}\vert ^{3/2})$. The pdf of horizontal velocity component v$_{x}$ is more symmetric and shows a similar super-Gaussian form with P(v$_{x})\sim $exp(-$\vert $v$_{x}$/v$_{xrms}\vert ^{3/2})$. These observations can be understood in terms of plume dynamics and are consistent with the instanton formulation that relates input and output statistics of turbulence. [Preview Abstract] |
Tuesday, March 22, 2005 12:39PM - 12:51PM |
J37.00008: LES Simulations of Turbulent Combustion in a Type Ia Supernovae Srabasti Dutta, James Glimm, Yongmin Zhang We propose a 2D axisymmetric model of a successful type $I_a$ supernova explosion, based on a front tracking sharp flame model. The calculation is free of adjustable turbulent transport parameters, and in this sense is in the spirit of LES turbulence simulations. Since the mixing is dominated by the largest eddies, resolving these and not the smaller ones results in a tolerable error. Both the 2D and the LES nature of the model greatly simplify parameter identification. The 2D model allows multiple simulations and an exploration of unknown parameters, while the LES model removes parameters from the simulation. We take first steps in the parameter identification problem, in observing that the initial conditions (initial radius and initial perturbation amplitudes, for example) are senstitive in determining the success of the explosion. [Preview Abstract] |
Tuesday, March 22, 2005 12:51PM - 1:03PM |
J37.00009: Intermittency in two dimensional turbulence Yonggun Jun, Jie Zhang, Xiao-Lun Wu Intermittency of the velocity difference $\delta v_{l}$ and the energy dissipation rate $\varepsilon_{l}$ on scale of $l$ is investigated on the inverse energy cascade range in the forced 2D turbulent flow. Measurements are performed on the freely-suspended horizontal soap film using particle tracking velocimetry. We use the multifractal method to analyze the energy dissipation rate $\varepsilon_{l}$ and calculate the scaling exponent $\tau_{q}$ and the intermittency parameter $\mu_{\varepsilon}$. From high order structure function $\left<\left(\delta v\right)\right>^{p}\sim l^{\zeta_{p}}$, We obtain the scaling exponent $\zeta_{p}$ with integer $p$ and estimate the intermittency parameter $\mu_{v}$. The Komogorov refined hypothesis suggests the relation $\zeta_{p}=\tau_{p/3}+p/3$. This relation agrees with the experimental data up to $p=5$. The deviation for larger $p$ may be due to linear damping in the system that also contributes to the energy flux on large scales. [Preview Abstract] |
Tuesday, March 22, 2005 1:03PM - 1:15PM |
J37.00010: Instabilities in Bubble Pinch-Off J.C. Burton, R. Waldrep, P. Taborek When gas is released from a submerged nozzle, the bubbles must separate and pinch-off before rising to the surface. This process involves a singularity in the flow as the diameter of the neck shrinks to zero. We present high-speed videos (100,000 fps) of bubble pinch-off in a variety of fluids with viscosities ranging from .01 Poise (water) to 120 Poise (silicone oil). The forces involved in the pinch-off come from surface tension, inertia and viscous dissipation. In viscous fluids, surface tension and viscosity are balanced and the neck shrinks linearly in time to beyond optical resolution. When the viscosity of the exterior fluid is sufficiently small (i.e. water), inertia dominates the flow and the neck diameter shrinks with $\tau^{1/2}$, where $\tau$ is the time remaining until pinch-off. In the low viscosity regime, we find that the flow becomes unstable, and the neck ruptures at a typical length scale of 100 $\mu$m and a time scale of $\tau$=10 $\mu$s. The acoustic signature of this instability will also be presented. [Preview Abstract] |
Tuesday, March 22, 2005 1:15PM - 1:27PM |
J37.00011: Conformation-triggered flow instability in monolayer thick polymer films Sergei Sheiko, Hui Xu, David Shirvanyants, Kathryn Beers, Krzysztof Matyjaszewski, Michael Rubinstein, Andrey Dobrynin Here we have report on a new type of flow instability triggered by conformational changes of brush-like macromolecules as they spread on a solid substrate. By tracing the movement of individual molecules by atomic force microscopy, we were able to follow the evolution of the instability pattern on the molecular level enabling a microscopic understanding of the underlying physical mechanism. The instability is an analog of the Saffman-Taylor instability in thin films. However, the instability is driven by a variation in flow velocity controlled by molecular conformation instead of a viscosity gradient. [Preview Abstract] |
Tuesday, March 22, 2005 1:27PM - 1:39PM |
J37.00012: A Dynamical Model of Molecular Monolayers: Why Tethers Don't Snap Elizabeth K. Mann, Lu Zou, Andrew Bernoff, James Alexander, J. Adin Mann A bola-shaped domain in a Langmuir monolayer at the air/water interface relaxes towards a circular shape under the influence of line tension. The ``tether'' thickens continuously in this process, in marked contrast to the Hele-Shaw and the three-dimensional cases, where hydrodynamic instabilities lead to the tether snapping. A simplified dynamical model allows us use lubrication theory to explain this without incorporating repulsive forces to stabilize the tether in 2D. The model also allows us to give a better estimate of line tensions from the relaxation rate of such monolayer domains. This material is based upon work supported by the National Science Foundation under Grant No.9984304. [Preview Abstract] |
Tuesday, March 22, 2005 1:39PM - 1:51PM |
J37.00013: Marangoni Convection and Deviations from Maxwell's Evaporation Model Phil Segre, Eddie Snell, Dan Adamek We investigate evaporation and natural convection from thin pools of volatile liquids. We find that evaporation rates do not always follow the classical Maxwell evaporation model; deviations become larger with increasing liquid volatility. Thermal imaging shows that the liquids are not always stable to Marangoni convection; surface flows grow in strength with increasing volatility. A highly sensitive thermal imaging camera allows us to characterize the Marangoni patterns as a function of volatility, time, and liquid pool height. To help explain our results, we develop a heat balance model to connect the evaporation rates to the convective dynamics, and show that the convective flows are the source of the deviations from Maxwells' evaporation model. [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