Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session RU: Particle Laden Flows III |
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Chair: Evan Variano, University of California, Berkeley Room: Hyatt Regency Long Beach Regency A |
Tuesday, November 23, 2010 3:05PM - 3:18PM |
RU.00001: Size distribution of droplets undergoing phase transition in homogeneous isotropic turbulence Briti Sundar Deb, Bernard J. Geurts, Herman J.H. Clercx, A.K. Kuczaj, Hans Kuerten We investigate the dynamics of an ensemble of discrete aerosol water droplets undergoing phase transition, expressed by evaporation and condensation, in a turbulent flow. Our focus is on the stationary distribution of droplet sizes that develops as a result of these phase transitions in forced, homogeneous, isotropic turbulence. For this purpose we perform direct numerical simulation (DNS) using a de-aliased pseudo spectral method in a domain with periodic boundary conditions. We solve the Navier-Stokes equations and additional equations for the temperature and background humidity against which the size of the droplets evolves by exchanging heat and mass. The motion of the droplets under Stokes drag force is time-accurately tracked. The responsiveness of the droplets to small turbulent scales is directly related to the size of the individual spherical droplets. The latter is changing due to evaporation and condensation, which in turn depends on the unique trajectory of the droplets in the unsteady flow. We compute the natural size distribution at various heat and mass transfer parameters and observe its dependency on the Reynolds number. [Preview Abstract] |
Tuesday, November 23, 2010 3:18PM - 3:31PM |
RU.00002: Multiple Particle Interaction at Intermediate Reynolds Numbers Acmae El Yacoubi, Sheng Xu, Z. Jane Wang The literature is rich with studies on particle interaction in Stokes flow. However, there are scant studies on particle interaction at intermediate Reynolds numbers. Here, we present a new computational scheme to simulate the dynamics of the particles coupled to the Naviers-Stokes solutions for the fluid. In order to understand the basic picture of particle-particle interactions in fluid, we investigate the dynamics of an array of freely falling cylinders with an initial spacing on the order of the particle diameter. We find that for a small number of particles ($n=3,~4$), there are two distinct falling configurations which depend on the parity of $n$. For $n>4$, the falling configuration is a mix of those previous modes. However, when the initial spacing between particles is below a threshhold, the array is separated into small clusters of $2$ or $3$ particles. We further quantify the interaction force between two falling particles as a function of their relative position, and compare them with results in the Stokes regime. [Preview Abstract] |
Tuesday, November 23, 2010 3:31PM - 3:44PM |
RU.00003: Possibility of perfect fluid flow from granular jet impact Jake Ellowitz, Nicholas Guttenberg, Herve Turlier, Wendy W. Zhang, Sidney R. Nagel Axisymmetric collision of a cylindrical water jet with a circular target generates a thin conical sheet, also known as a water bell [1]. Intriguingly, recent experiments on granular jet impact in the regime of dense inertial flow reveal similar behavior: the angles by which the collimated sheets of particles are ejected from the target [2] agree closely with the angles measured in the water-bell experiments. This quantitative correspondence suggests that the collective granular motion during impact can be modeled as an incompressible, continuum fluid. Since viscous effects are weak in water-jet impact and the granular jet is comprised of non-cohesive particles (hence possessing zero surface tension), the simplest scenario is that the continuum motion corresponds to the flow of a perfect fluid. We assess this possibility by comparing exact solutions of 2D Euler-jet impact with 2D discrete-particle simulations of granular impact. We also construct approximate solutions for axisymmetric Euler-jet impact and compare these with granular-impact experiments.\newline [1] Cheng et al. Phys. Rev. Lett. 99, 2007.\newline [2] Clanet, C. J. Fluid Mech. 430, 2001. [Preview Abstract] |
Tuesday, November 23, 2010 3:44PM - 3:57PM |
RU.00004: Gas and particulate phase velocity measurements of a high-speed gas jet into a two-dimensional bubbling fluidized bed Alexander Mychkovsky, Steven Ceccio A Laser Doppler Velocimetry (LDV) technique was implemented to simultaneously measure the gas and particulate phase velocities in a high-speed jet plume in a two-dimensional (2D) bubbling fluidized bed. The gas and particulate phase velocity profiles are presented and analyzed. This includes similarity profile scaling as well as volume fraction, mass flow, and momentum transport calculations for the two phases. Furthermore, applying the Eulerian equation of motion to the particulate phase with the measured velocity profiles, the bed particle drag coefficient is recovered and is found to be consistent with the established empirical value. [Preview Abstract] |
Tuesday, November 23, 2010 3:57PM - 4:10PM |
RU.00005: An experimental technique for simultaneous measurement of fluid flow and particle kinematics in particle-laden flows Audric Collignon, Evan Variano A significant challenge facing laboratory measurements of particle-laden flow is the simultaneous resolution of both fluid and particle phases. We present a simple technique to resolve the kinematics of individual particles and the surrounding flow. Most importantly, this technique reveals the full angular velocity vector of each particle. We use water as our fluid (allowing high Reynolds number flow) and particles that have the same refractive index as water. Results from spherical hydrogel particles will be presented and other options will be discussed. Refractive index matching allows light to propagate undisturbed through particles, even at high volume loading. We apply PIV simultaneously to the fluid phase and to the interior of each particle. We then use the velocities measured inside each particle to solve an inverse problem giving particle location, translation and angular velocity. We present the technique, including details of the optical setup and image processing methods. We also present a validation and uncertainty analysis covering random and bias errors. [Preview Abstract] |
Tuesday, November 23, 2010 4:10PM - 4:23PM |
RU.00006: Finite-size particles in turbulence: effect of particle shape and rotational dynamics Gabriele Bellani, Evan A. Variano In this laboratory study we investigate the two-way coupling between rigid particles and homogeneous isotropic turbulence. Turbulence Reynolds number is Re$_\lambda \approx 350$ and the particle length and time scales are within the inertial sub-range. We focus on the effects of particle shape and rotation. Rotational dynamics play an important role in inter-phase momentum exchange, especially for non-spherical particles. A novel technique resolves particle velocity and rotation, simultaneously with fluid-phase velocities. From these measurements we analyze the inter-phase coupling of both translational and rotational motion. Analysis includes correlations between particle motion and the surrounding fluid, wake dynamics, and particle motion statistics. Effect of particles on the turbulent flow is investigated from the fluid-phase turbulent kinetic energy and dissipation rates. [Preview Abstract] |
Tuesday, November 23, 2010 4:23PM - 4:36PM |
RU.00007: Coffee ring deposition in bands Shreyas Mandre, Ning Wu, Joanna Aizenberg, Lakshminarayanan Mahadevan Microscopic particles suspended in a liquid are transported and deposited at a contact line, as the contact line recedes due to evaporation. A particle layer of uniform thickness is deposited if the particle concentration is above a threshold; below this threshold the deposit forms periodic bands oriented parallel to the contact line. We present a model for the formation of these bands based on evaporation leading to the breakup of the thin liquid film near the contact line. The threshold results from a competition between evaporation speed and deposition speed. Using this model, we predict the thickness and length of the bands, making the control of patterned deposition possible. [Preview Abstract] |
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