Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session R3: Multiphase Flows VIII |
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Chair: Anthony Rosato, New Jersey Institute of Technology Room: 325 |
Tuesday, November 26, 2013 1:05PM - 1:18PM |
R3.00001: First particle acceleration measurements for a shocked multiphase flow at a new horizontal shock tube facility Greg Orlicz, Adam Martinez, Kathy Prestridge The horizontal shock tube at Los Alamos, used for over 20 years to study shock-driven mixing between different density gases, has been retrofitted with a new particle seeding system, test section, and diaphragmless driver to investigate the unsteady forces on particles as they are accelerated by a shock wave. Current experiments are performed to measure the acceleration of dispersed glycol droplets, with nominal 0.5 $\mu $m diameter, carried in ambient air. Measurements at this facility will be used to develop and validate empirical models implemented in numerical codes. A Particle Image Velocimetry/Accelerometry (PIVA) system is implemented at the facility using eight laser pulses and an eight-frame high speed camera. The lasers are 532 nm Nd:YAGs with pulse widths of 20 ns, and the camera is a Specialised Imaging SIMD with 1280x960 resolution at up to 7 million frames per second. With this PIVA arrangement, eight particle fields are collected by independently varying the interframe times. Seven velocity and six acceleration fields are used to study the unsteady drag on the particles. Initial data sets are with a size distribution of known particle diameters. Plans are to vary the particle/gas density ratio, particle diameters, and particle phase (liquid/solid). [Preview Abstract] |
Tuesday, November 26, 2013 1:18PM - 1:31PM |
R3.00002: Measurements of Multiphase Fluid Mixing Using Synchrotron X-Ray Fluorescence Alan Kastengren, Benjamin Halls, Terry Meyer Multiphase flows can prove problematic for the use of optical diagnostics due to the strong interaction of visible light with phase boundaries. X-ray absorption and phase-contrast imaging have been successfully used to probe multiphase fluid flows under a wide variety of conditions. This presentation will describe the use of another technique, x-ray fluorescence spectroscopy, to probe an impinging jet spray flowfield. The x-ray fluorescence technique will be described, including its advantages and drawbacks compared to other techniques, both optical and x-ray. Preliminary results from the impinging jet flowfield show that the fluid from each initial jet tends to congregate on the side of the sheet formed after the impingement point opposite the jet. This behavior was not expected prior to these measurements, demonstrating the utility of the fluorescence technique to probe the mixing of the two streams. Other potential applications for the x-ray fluorescence technique will also be briefly discussed. [Preview Abstract] |
Tuesday, November 26, 2013 1:31PM - 1:44PM |
R3.00003: Role of fluctuations in instability generation in gas-solid suspensions Shankar Subramaniam, Mohammad Mehrabadi, Ravi Kolakaluri, Sudheer Tenneti Stability analysis of gas-solid suspensions using kinetic theory (Koch, Phys. Fluids, 1990) relies on a number density function (NDF) that is based on the canonical (constant number) ensemble. Euler-Lagrange simulations of a model problem are used to show that this approach does not accurately represent the scale--dependent interphase coupling between different realizations of the gas velocity field and fluctuations in the number of particles naturally occurring in fluidized beds. The grand-canonical (or variable number) ensemble is better suited to representing this coupling, and it is shown how the NDF can be related to this ensemble. The evolution of the grand-canonical NDF then leads to instabilities and growth of spatial fluctuations in the number density of a homogeneous suspension. This analysis leads to a different explanation for the growth of instabilities in homogeneous gas-solid suspensions that does not require perturbations in the average number density. Rather it is shown that the interaction of different realizations of the gas velocity field with individual realizations of the particle field leads to the growth of instabilities due to the dependence of drag on local volume fraction in each realization, that is extracted from particle-resolved DNS data. [Preview Abstract] |
Tuesday, November 26, 2013 1:44PM - 1:57PM |
R3.00004: Towards large-eddy simulation of multiphase flows using two-way coupled, Euler-Lagrangian methods Wyatt Horne, Krishnan Mahesh Two-way coupled Euler-Lagrangian methods are sensitive to the size of the particle with respect to the Eulerian grid. We develop an interpolation methodology that addresses this issue for unstructured grids. The carrier fluid is solved using large-eddy simulation (LES) including finite size effects and force coupling from the Lagrangian particles. The Lagrangian particle motion is solved using equations relating the motion of the carrier fluid to forces on each discrete particle. Interpolation of Lagrangian quantities to Eulerian quantities is performed using interpolation kernels dependent on particle size that are volume averaged over control volumes. This interpolation technique is compared to other interpolation methods over several canonical flow cases. It is found from these comparisons that the developed interpolation technique is capable of producing more accurate results. Results are shown for both bubbles and solid particles. Simulations of a single sphere rising in an inclined channel under conditions similar to an experiment conducted by Lomholt et al. [Int. J. Multiphase Flow (2002) \textbf{28}:225--246] are performed. Good agreement is found between the experimental and simulated particle trajectories and velocity profiles. [Preview Abstract] |
Tuesday, November 26, 2013 1:57PM - 2:10PM |
R3.00005: Eulerian-Lagrangian Simulations of Bubbly Flows in A Vertical Square Duct Rui Liu, Surya P. Vanka, Brian G. Thomas We report results of Eulerian-Lagrangian simulations of developing upward and downward bubbly flows in a vertical square duct with a bulk Reynolds number of 5000. The continuous fluid is simulated with DNS, solving the Navier-Stokes equations by a second-order accurate finite volume fractional step method. Bubbles of sizes comparable to the Kolmogorov scale are injected at the duct entrance with a mean bulk volume fraction below 10$^{-2}$. A two-way coupling approach is adopted for the interaction between the continuous fluid phase and dispersed bubble phase. The bubbles are tracked by a Lagrangian method including drag and lift forces due to buoyancy and Saffman lift. A in-house code, CU-FLOW, implemented on Graphic Processing Unit (GPU) is used for simulations in this work. The preferential distributions of bubbles and their impact on local turbulence structures and their effects on turbulent kinetic energy budgets are studied. Results between an upward flow and a downward flow with the bubbles are compared. [Preview Abstract] |
Tuesday, November 26, 2013 2:10PM - 2:23PM |
R3.00006: Low Reynolds-number hydrodynamics of immersed fluid sheets Neil Ribe, Bingrui Xu Low Reynolds-number flows of thin bodies of viscous fluid immersed in an external fluid with a different viscosity occur in contexts ranging from microfluidics to global geophysics. Here we study the buoyancy-driven motion of a two-dimensional sheet with thickness $h$ and viscosity $\eta_2$ in a less dense fluid with viscosity $\eta_1$, starting from an initial geometry that corresponds to subduction of oceanic lithosphere in Earth's mantle. We work with two different representations of the flow: a full boundary-integral formulation, and a new ``hybrid'' integral equation that combines asymptotic thin-sheet theory with a boundary-integral representation of the external flow. In both cases, the time-dependent motion of the sheet is obtained by updating the geometry after each instantaneous flow solution. A scaling analysis shows that the sheet's velocity is controlled by its dimensionless ``stiffness'' $S\equiv (\eta_2/\eta_1) (h/\ell_b)^3$, where the ``bending length'' $\ell_b$ is the length of the portion of the sheet's midsurface where bending moments are significant. We will present illustrative simulations of the evolving sheet as a function of the viscosity ratio $\eta_2/\eta_1$, and will assess the relative efficiencies of the full boundary-integral and hybrid approaches. [Preview Abstract] |
Tuesday, November 26, 2013 2:23PM - 2:36PM |
R3.00007: Extension of the Mass-Conserving Level-Set method to unstructured polyhedral control volumes for two-phase flows Fahim Raees, Duncan R. van der Heul, Kees Vuik In this research, we present the Mass-Conserving Level-Set method (MCLS) for the simulation of two-dimensional, incompressible, immiscible two-phase flows, using a discretisation scheme that can accurately and efficiently handle domains of arbitrary geometrical complexity. The level set and the volume of fluid fraction are evolved at each time step on unstructured triangular grids. The Higher-Order Discontinuous Galerkin finite element method is used for spatial discretisation of the level set advection equation. The volume of fluid fraction advection is done in geometrical manner using Lagrangian-Eulerian method. This method is accurately mass conserving and easy to implement on unstructured grids. Also, it avoids overlapping regions during the volume of fluid fraction advection. The advected level set is corrected locally to make it mass conserving by the means of an explicit, invertible relation between the local level set and the volume of fluid fraction. This relation is termed as a Volume-of-Fluid function. The results show that proposed method is accurately mass conserving. Also, higher-order convergence is highlighted with this method on unstructured grids for the different test cases. [Preview Abstract] |
Tuesday, November 26, 2013 2:36PM - 2:49PM |
R3.00008: Computational simulation of the interactions between water waves and two-dimensional wave energy converters Amirmahdi Ghasemi, Ashish Pathak, Robert Chiodi, Mehdi Raessi Ocean waves represent a vast renewable energy resource, which is mostly untapped. We present a computational tool for simulation of the interactions between waves and two-dimensional oscillating solid bodies representing simple wave energy converters (WECs). The computational tool includes a multiphase flow solver, in which the two-step projection method with GPU acceleration is used to solve the Navier-Stokes equations. The fictitious domain method is used to capture the interactions of a moving rigid solid body with the two-fluid flow. The solid and liquid volumes are tracked using the volume-of-fluid (VOF) method, while the triple points and phase interfaces in three-phase cells are resolved. A consistent mass and momentum transport scheme is used to handle the large density ratio. We present results of two wave generation mechanisms with a piston or flap wave maker, where the theoretical and experimental results were used for validation. Then, simulation results of several simple devices representative of distinct WECs, including a bottom-hinged flap device as well as cylindrical or rectangular terminators are presented. The results are in good agreement with the available experimental data. [Preview Abstract] |
Tuesday, November 26, 2013 2:49PM - 3:02PM |
R3.00009: Simulating immiscible multi-phase flow and wetting with 3D stochastic rotation dynamics (SRD) Thomas Hiller, Marta Sanchez de La Lama, Stephan Herminghaus, Martin Brinkmann We use a variant of the mesoscopic particle method stochastic rotation dynamics (SRD) to simulate immiscible multi-phase flow on the pore and sub-pore scale in three dimensions. As an extension to the multi-color SRD method, first proposed by Inoue et.al., we present an implementation that accounts for complex wettability on heterogeneous surfaces. In order to demonstrate the versatility of this algorithm, we consider immiscible two-phase flow through a model porous medium (disordered packing of spherical beads) where the substrate exhibits different spatial wetting patterns. We show that these patterns have a significant effect on the interface dynamics. Furthermore, the implementation of angular momentum conservation into the SRD algorithm allows us to extent the applicability of SRD also to micro-fluidic systems. It is now possible to study e.g. the internal flow behaviour of a droplet depending on the driving velocity of the surrounding bulk fluid or the splitting of droplets by an obstacle. [Preview Abstract] |
Tuesday, November 26, 2013 3:02PM - 3:15PM |
R3.00010: Vertical gas injection into liquid cross-stream beneath horizontal surfaces In-ho Lee, Simo Makiharju, Inwon Lee, Marc Perlin, Steve Ceccio Skin friction drag reduction on flat bottomed ships and barges can be achieved by creating an air layer immediately beneath the horizontal surface. The simplest way of introducing the gas is through circular orifices; however the dynamics of gas injection into liquid cross-streams under horizontal surfaces is not well understood. Experiments were conducted to investigate the development of the gas topology following its vertical injection through a horizontal surface. The liquid cross-flow, orifice diameter and gas flow rate were varied to investigate the effect of different ratios of momentum fluxes. The testing was performed on a 4.3 m long and 0.73m wide barge model with air injection through a hole in the transparent bottom hull. The incoming boundary layer was measured via a pitot tube. Downstream distance based Reynolds number at the injection location was 5 x 10\textasciicircum 5 through 4 x 10\textasciicircum 6. To observe the flow topology, still images and video were recorded from above the model (i.e. through the transparent hull), from beneath the bottom facing upward, and from the side at an oblique angle. The transition point of the flow topology was determined and analyzed. [Preview Abstract] |
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