Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session HB: Turbulent Mixing I |
Hide Abstracts |
Chair: Thomas Ward, North Carolina State University Room: 001B |
Monday, November 24, 2008 10:30AM - 10:43AM |
HB.00001: Tomo-PIV Measurement of High Reynolds Number Dissipation Scale Structures Nicholas Worth, Timothy Nickels Understanding the sources of dissipative intermittency in high Reynolds number turbulence is of significant interest, especially given the increasing affordability of LES. Coherent dissipation scale structures have been identified in numerous numerical and experiment investigations, although the latter are typically restricted by the need for accurate resolution of extremely small fast motions. These investigations are therefore often limited to one-dimensional measurements, making the study of these 3D structures and their relationship to the dissipation field difficult. The current investigation employs a very large water mixing tank (2m in diameter), which uses counter-rotating impellors to generate high Reynolds number turbulence ($R_{\lambda} \approx1000$) that is close to isotropic and homogeneous. The large scale of the tank brings the smallest scales within the resolution of Tomo-PIV, allowing full 3D realization of these structures. This unique experimental setup presents a number of challenges, which include: seeding density limitations imposed by optical attenuation through the tank; demanding light sheet intensity requirements; and the extremely high computational cost of Tomographic reconstruction for the thousands of velocity fields required for statistical analysis. Initial results will be presented along with future plans for measurement refinement. [Preview Abstract] |
Monday, November 24, 2008 10:43AM - 10:56AM |
HB.00002: Experimental Research on Turbulent Bubbly Mixing Layer Flow with Polymer Additives Fang Guo, Bin Chen, Fude Guo Based on turbulent mixing layer flow with polymer additives, bubbly two-phase mixing layer with polymer additives were experimentally investigated by PIV to study the interaction between bubble and coherent structure in viscoelastic fluid with The velocity ratio 4:1. Gas bubbles with gas fraction 0.5{\%} were injected both of water with and without 200ppm Polymer additives from high speed side, low speed side and central line of the mixing layer. Similar with single-phase Newtonian and viscoelastic fluid, the Reynolds stress and voticity of two-phase flow cases still concentrate in a coniform area of central mixing flow field part and the width will increase with increasing the Reynolds number. It also shows that the mixing layer spreads linearly and the Reynolds stresses are self-similar both in single phase, but it is quite different in multiphase. However, compared with single-phase, the peak value of Reynolds shear stress will decrease and there will be fluctuations when bubbles were injected into water with and without polymer additives. As to the maximum value of vorticity on different cross-section, it will decrease with the development of mixing layer and the injection of bubbles will slower the speed of this tendency. [Preview Abstract] |
Monday, November 24, 2008 10:56AM - 11:09AM |
HB.00003: Experimental study of JPDF and conditional diffusion in three-stream mixing Matthew Dinger, Jian Cai, Chenning Tong, Campbell Carter, Michael Ryan Three-stream scalar mixing is studied using flows issued from a center jet and an annulus into co-flow air. Rayleigh scattering and planar laser-induced fluorescence are used to obtain the mass fractions of the fluid from the jet ($\phi_1$) and the annulus ($\phi_2$). The JPDF of these mass fractions shows remarkable similarities to that of mixture fraction and temperature in nonpremixed reactive systems. The conditional scalar diffusion shows that diffusion generally transports the JPDF rapidly towards the conditional mean $\langle \phi_2 | \phi_1 \rangle$ and then relatively towards the peak of the JPDF. This suggests that the mixing of $\phi_2$ is faster than $\phi_1$. The results can be compared to measurements in flames to understand the mixing of mixture fraction and temperature and turbulence-chemistry interaction in flames. [Preview Abstract] |
Monday, November 24, 2008 11:09AM - 11:22AM |
HB.00004: Study of scalar fluctuations downstream of a mandoline in grid turbulence Sharadha Viswanathan, Stephen B. Pope We studied the decay of scalar fluctuations downstream of a heated mandoline in isotropic decaying grid turbulence. Probability Density Function (PDF) calculations are performed in conjunction with a modified Interaction by Exchange with the Conditional Mean (IECM) mixing model, in which the effects of molecular diffusion are directly incorporated in the mixing model as a mean conditional drift term. Previous experimental studies by Warhaft {\&} Lumley (1978) and Warhaft (1984) (henceforth referred to as W78 and W84 respectively) suggest the dependence of the scalar variance decay rate on the scalar-to-turbulence length scale ratio. On the other hand, Sreenivasan et al. (1980) report a decay rate independent of the length scale ratio for length scale ratios smaller than unity. The present model calculations for a range of length scale ratios show that the decay rate of scalar variance is independent of the length scale ratio (for the conditions of the experiment), when plotted against distance from the mandoline. Comparison of the present model calculations with the experimental measurements of W78 and W84 show good agreement and are also consistent with the observations of Sreenivasan et al. For large times, our model predicts a decay rate given by \textit{mC}$_{\phi}$, where $m$ is the velocity variance decay exponent and $C_{\phi}$ is a mixing model constant. [Preview Abstract] |
Monday, November 24, 2008 11:22AM - 11:35AM |
HB.00005: A fast, physically based method for mixing computations Patrice Meunier, Emmanuel Villermaux We introduce a new numerical method for the study of diffusing scalar filaments in a 2D advection field. The position of the advected filament is computed kinematically, and the associated convection-diffusion problem is solved using the computed local stretching rate, assuming that the diffusing filament thickness is smaller than its local radius of curvature. This assumption reduces the numerical problem to the computation of a single variable along the filament, thus making the method extremely fast and applicable to any Peclet number. This method is then used for the mixing of a scalar in the chaotic regime of a Sine Flow, for which we relate the global quantities (spectra, concentration PDF) to the distributed stretching of the convoluted filament. The numerical results indicate that the PDF of the filament elongation is log-normal, a signature of random multiplicative processes. This property leads to exact analytical predictions for the spectrum of the field and for the PDF of the scalar concentration, in good agreement with the numerical results. These are thought to be generic of the chaotic mixing of scalars in the Batchelor regime. [Preview Abstract] |
Monday, November 24, 2008 11:35AM - 11:48AM |
HB.00006: In-Cylinder Flow Through An Internal Combustion (IC) Engine Samira Khan, Kendrick Gibson, Paulius Puzinauskas, Yongli Qi IC engine performance is strongly influenced by large-scale in-cylinder motion developed during the intake process. This work was part of a larger effort to characterize and augment in-cylinder flow structures to improve lean limit and exhaust gas recirculation tolerance. Ultimately the flow structures are to be characterized with unsteady computational fluid dynamics (CFD) calculations. This study provided digital particle image velocimetry (DPIV) flow visualization data under steady conditions to improve the calibration of the CFD work. An engine cylinder head was mounted on a transparent cylinder with a fixed piston. Air was drawn through using a steady flow bench, and DPIV images were obtained from the cylinder. Measurements were made at four suction pressures and four valve lift to diameter ratios for a total of sixteen cases. After initial measurements, intake port modifications were made to enhance tumble. The modifications created more definitive tumble flow. [Preview Abstract] |
Monday, November 24, 2008 11:48AM - 12:01PM |
HB.00007: Temporal asymmetry in Lagrangian two-dimensional turbulence Robert Ecke, Colm Connaughton, Mahesh Bandi, Michael Rivera Turbulence is an irreversible process with a net flow of energy from large to small scales in three-dimensional systems and from small to large scales in two-dimensional flows for scales larger than the injection scale. A measure of this irreversibility is the energy dissipation or, equivalently, for an inertial cascade the energy flux between spatial scales. We study temporal symmetry breaking in experimental and numerical studies of two-dimensional turbulence. We demonstrate that symmetry breaking in low-order Lagrangian correlation functions depends on the local Eulerian scale-to-scale energy transfer. [Preview Abstract] |
Monday, November 24, 2008 12:01PM - 12:14PM |
HB.00008: Lagrangian statistics in confined two-dimensional turbulence Kai Schneider, Benjamin Kadoch, Wouter J.T. Bos We present a Lagrangian study of two-dimensional turbulence for two different geometries, a periodic and a confined circular geometry (PRL 100, 184503 (2008)). The influence of no-slip boundaries on the Lagrangian dynamics is investigated. It is found that the Lagrangian acceleration is even more intermittent in the confined domain than in the periodic domain. The flatness of the Lagrangian acceleration as a function of the radius shows that the influence of the wall on the Lagrangian dynamics becomes negligible in the center of the domain, and it also reveals that the wall is responsible for the increased intermittency. The transition in the Lagrangian statistics between this region, not directly influenced by the walls, and a critical radius which defines a Lagrangian boundary layer is shown to be very sharp with a sudden increase of the acceleration flatness from about 5 to about 20. [Preview Abstract] |
Monday, November 24, 2008 12:14PM - 12:27PM |
HB.00009: Anisotropy and intermittency in the turbulent shearless mixing Michele Iovieno, Daniela Tordella We focus on velocity and velocity derivative statistics in the decaying shearless turbulent mixing. The data are obtained by means of direct numerical simulations. The flow is generated by the interaction of two decaying isotropic turbulent flows of differing kinetic energies by equal macroscale. The Taylor microscale Reynolds number ranges from 45 to 150. Inside the mixing layer the velocity statistics depart from the quasi-Gaussian values observed in the homogeneous external regions, and show a high level of large scale intermittency. Anisotropy was found to be mild for the velocity second order moments but very intense on higher order velocity moments: the moments in the nonhomogenous direction are almost twice than those in the normal directions. Inside the mixing, longitudinal derivative third moments in the direction of the mixing present a minimum, while the moments along the normal directions present a maximum. A ratio 4 it is observed. For the kurtosis this ratio decreases to 1.24. The variation of the longitudinal derivative skewness across the mixing is of $\sim $ 0.8, to be compared with a variation of 0.04 in the isotropic regions, a value which can be taken as a measure of the numerical accuracy. [Preview Abstract] |
Monday, November 24, 2008 12:27PM - 12:40PM |
HB.00010: Enhancement of Turbulent Heat Transfer in Channel Flow Using a Rectangular Cylinder Mamoru Senda, Dong-Hyeog Yoon, Kyung-Soo Yang The large-scale vortices shed from a cylindrical object as a vortex generator can be used to enhance heat transfer in a heat exchanger. In this study, Large-Eddy Simulation of turbulent heat transfer in channel flow with a rectangular cylinder at \textit{Re}=3000 (based on uniform inlet velocity and cylinder height) and \textit{Pr}=0.7 was performed with four distinct values of cylinder aspect ratio (horizontal to vertical, AR=0.5, 1.0, 2.0, and 3.0) to identify its effect on the heat transfer characteristics in the vicinity of the channel wall heated with constant heat flux. The rectangular cylinder is located on the centerline of the channel flow, causing flow separation and Karman vortices. Flow separates at the upstream edges of the cylinder, but it may reattach on the upper and lower faces of the cylinder for larger AR. Thus flow topology drastically alters across the threshold AR, implying significant change in flow characteristics such as turbulence intensity, wall shear stress, and secondary vortices in the vicinity of the channel walls, which in turn affect the heat transfer capacity on the channel walls. The effect of AR and the related flow physics are discussed in detail. [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