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 A3: Multiphase Flows I |
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Chair: Gustaf Jacobs, San Diego State University Room: 325 |
Sunday, November 24, 2013 8:00AM - 8:13AM |
A3.00001: Acceleration of non-Newtonian multiphase flow computations via CPU-GPU platforms Arturo Fernandez Modeling of multiphase flow involving non-Newtonian fluids presents special challenges due to the wide range of scales associated with these systems. The reproduction of viscoelastic properties can be done either using constitutive equations derived from kinetic theory or by modeling the dynamics of suspension of macromolecules at the mesoscopic or molecular scale. We present results combining front-tracking with Brownian dynamics simulations, which capture non-Newtonian properties at the mesoscopic scale in a more realistic fashion but at the expense of higher computational cost. We discuss the acceleration of the computations using CPU-GPU platforms. The continuum simulations are carried out in CPUs as usual but the Brownian dynamics simulations are parallelized so they can be performed in GPUs. The examples include the settling of a solid particle in an elastic fluid, the so-called standard case, and the deformation of an elastic drop in a simple shear flow. Good agreement between experimental and numerical results is found. [Preview Abstract] |
Sunday, November 24, 2013 8:13AM - 8:26AM |
A3.00002: Buoyancy effects on rotation and translation of large particles in turbulent flow Margaret Byron, Yiheng Tao, Evan Variano We use laboratory experiments to investigate the effects of homogeneous, isotropic turbulence on particles of varying buoyancy, size, and shape. The buoyancy is varied between a specific gravity of 1.001 and 1.05. All particles are roughly 1 cm, which in this flow is close to Taylor's turbulent microscale. We vary the shape to compare spherical particles to non-spherical particles while matching the settling velocity, volume, and/or surface area. Particles are fabricated in custom shapes using transparent hydrogels whose refractive index is close to water. We embed tracers within the particles and use PIV to image the interior of the particle simultaneously with the exterior flowfield of homogeneous isotropic turbulence, generated by two active-grid synthetic jet arrays. We find that the settling velocity of these particles, regardless of shape, is reduced relative to the quiescent settling velocity as predicted by the Clift-Gauvin model. We explore the distribution of rotation rates, as characterized by the variance of angular velocity. We find significant anisotropy in the angular velocities of negatively buoyant particles, which vanishes as particles approach neutral buoyancy. We also see differences in angular velocity distribution between particles of varying eccentricity. [Preview Abstract] |
Sunday, November 24, 2013 8:26AM - 8:39AM |
A3.00003: Experimental Investigation of Two Phase Fluid Flow and Passive Scalar Mixing around a Periodic Array of Spheres Mahdi Ramezani, Shankar Subramaniam, Michael Olsen Solid-liquid two-phase flow occurs in colloidal suspensions in a variety of applications, from catalytic reactions in chemical plants to bio oil production reactors. Detailed experimental study of these flows can both improve the understanding of the underlying phenomena and also assist in the development of accurate computational modeling. In the presented work, particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) are used to collect quantitative velocity and scalar field data in a liquid flow containing solid spheres. The velocity and scalar data are collected with sufficient spatial resolution to accurately capture turbulent flow statistics, allowing for precise validation of numerical models. This study is focused on presenting experimental data for periodic arrays of spheres that can be efficiently modeled numerically. For example, one flow geometry investigated consists of a square duct incorporating 5 spheres in line in the axial direction in the middle of the channel. Mixing of a passive scalar as well as the velocity field for this configuration of particles will be presented in the range of Reynolds numbers 50-400 and volume fractions of 5 to 20 percent. [Preview Abstract] |
Sunday, November 24, 2013 8:39AM - 8:52AM |
A3.00004: A unified model from dense and dilute compressible multiphase flows - application to explosive dispersal Y. Ling, S. Balachandar, T.P. McGrath, J. St. Clair Compressible multiphase flows are commonly seen in nature and industrial applications, such as volcanic eruptions and multiphase explosions. A fundamental challenge in modeling of compressible multiphase flows arise from rapid evolution of the volume fraction of the dispersed phase. For example, in multiphase explosions, the volume fraction of particles can change from the close-packing limit to lower than 1\% in milliseconds. Since the dominant physics are substantially different in the dense and dilute multiphase flow regimes, the models in the literature for these two regimes are typically different. To accurately simulate compressible multiphase flows involving fast transition from dense to dilute regimes, a novel model that covers both dense and dilute regimes is proposed in this study. A particle volume fraction equation is introduced, which reduces to the particle compaction equation in the dense regime. The present model also includes the added-mass force in the interphase coupling, which has been shown to be important in capturing shock-particle interaction in previous studies. A characteristic analysis of the present model is performed and the effect of added-mass force on acoustic speed of the multiphase system is also analyzed. [Preview Abstract] |
Sunday, November 24, 2013 8:52AM - 9:05AM |
A3.00005: A new drag force model based on drift flux for gas-particle two-phase flow Zhi Shang, Jing Lou, Hongying Li A drag force model was developed to simulate gas-particle two-phase flows. The drag force model was based on the gradients of the drift flux by considering the centrifugal force on the solid particles. According to the gradients of the drift flux, the terminal velocities of the dispersed phase (solid particles) were able to be calculated by the revised gravity. Through the numerical simulations comparing with the experiments and the simulations of the traditional k-$\varepsilon $-Ap and k-$\varepsilon $-kp models, this model was validated. [Preview Abstract] |
Sunday, November 24, 2013 9:05AM - 9:18AM |
A3.00006: Analysis of turbulent cavitating flow in a micro channel Christian Egerer, Stefan Hickel, Steffen Schmidt, Nikolaus Adams Associated with the collapse of vapor cavities is the formation of shock waves and liquid micro-jets, which can lead to the damage of material (cavitation erosion) or even failure of engineering devices, e.g. fuel injectors. We performed Large-Eddy Simulations of the turbulent cavitating flow through a micro channel, resembling a throttle valve commonly found in fuel injectors, at two different operating points with the aim of indentifying such erosion sensitive areas. The underlying numerical method of our flow solver INCA solves the compressible Navier-Stokes equations on a Cartesian adaptive grid for a homogeneous mixture of liquid and vapor in order to account for all relevent physical effects, i.e., compressibility of the liquid-vapor mixture as well as transitional flow and turbulence. The effect of non-represented scales on the represented ones is accounted for by the Adaptive Local Deconvolution Method, a non-linear finite volume scheme for the convective fluxes. We will present a comparison of numerical results with experiments as well as a detailed analysis of the interplay between vortical and cavitation structures. Furthermore, tools enabling the automatic detection of erosion sensitive areas will be discussed and applied. [Preview Abstract] |
Sunday, November 24, 2013 9:18AM - 9:31AM |
A3.00007: Pressure-driven displacement of a viscoplastic material by a Newtonian fluid Pinakinarayan Swain, George Karapetsas, Omar Matar, Kirti Sahu The pressure-driven displacement of a non-Newtonian fluid by a Newtonian fluid in a two-dimensional channel is investigated via a multiphase lattice Boltzmann method using a non-ideal gas equation of state well-suited for two incompressible fluids. We validate the code by comparing the results obtained using different regularized models, proposed in the literature, to model the viscoplasticity of the displaced material. Then, the effects of the Bingham number, which characterises the behaviour of the yield-stress of the fluid and the flow index, which reflects the shear-thinning/thickening tendency of the fluid, are studied. We find that increasing the Bingham number and increasing the flow index increases the size of the unyielded region of the fluid in the downstream portion of the channel and increases the thickness of the residual layer. This in turn decreases the interfacial instabilities and the speed of the propagating finger. [Preview Abstract] |
Sunday, November 24, 2013 9:31AM - 9:44AM |
A3.00008: Flow of a particulate mixture in a micro-channel Weitao Wu, Nadine Aubry, Mehrdad Massoudi We consider the flow of a mixture of granular materials and a viscous fluid in a micro-channel. We use Mixture Theory to treat this problem as a two-component system. One component (the granular materials) is modeled as a generalized Reiner-Rivlin type fluid, which not only considers the effects of volume fraction but also has a viscosity which depends on the shear rate. The other component (the host fluid) is assumed to behave as a linear viscous fluid. Lift and drag forces exerted by the fluid onto the discrete (solid) particles are taken into account. In order to gain insight into the nature and influence of the various terms in the two phase model we perform a parametric study. Results for the volume fraction and the velocity profiles will be presented. [Preview Abstract] |
Sunday, November 24, 2013 9:44AM - 9:57AM |
A3.00009: Two-Phase Flow Frictional Characteristics in Porous Wall Bounded Microchannels Eon Soo Lee, Julie Steinbrenner, Carlos Hidrovo, Kenneth Goodson, John Eaton This presents experimental results from small rectangular channels for fuel cells in which three of the channel walls are smooth, impermeable solid and the fourth wall is a porous gas-diffusion layer.~ Experiments were performed on a straight 200 by 500 micron by 150 mm long rectangular channel. Three walls of the channel were machined into a solid piece of acrylic. One of the 500 micron wide walls was a commercial Toray carbon paper Gas-Diffusion Layer (GDL) material held in place by a flat sheet of acrylic.~ Water was forced through the GDL layer from four evenly spaced holes in the flat acrylic piece.~ A one-dimensional, two-phase flow model was developed which included the effect of air and water flows in both the channel and GDL. The analysis from experimental measurements showed that the product of the friction factor and the gas flow Reynolds number was very nearly a constant, indicating that the model captures the critical physical features of the flow and is useful for the prediction of gas flow rate or pressure drop in a fuel cell microchannel. [Preview Abstract] |
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