Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session H28: Particle-laden Flows: General II |
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Chair: Andrea Prosperetti, Johns Hopkins University Room: F149 |
Monday, November 21, 2016 10:40AM - 10:53AM |
H28.00001: Closing the reduced position-space Fokker-Planck equation for shear-induced diffusion using the Physalis method Adam J. Sierakowski, Laura J. Lukassen In the shear flow of non-Brownian particles, we describe the long-time diffusive processes stochastically using a Fokker-Planck equation. Previous work has indicated that a Fokker-Planck equation coupling the probability densities of position and velocity spaces may be appropriate for describing this phenomenon (Lukassen \& Oberlack, Phys.~Rev.~E 89, 2014). The stochastic description, integrated over velocity space to obtain a reduced position-space Fokker-Planck equation, contains unknown space diffusion coefficients. In this work, we use the Physalis method for simulating disperse particle flows (Sierakowski \& Prosperetti, J.~Comp.~Phys., 2016) to verify the colored-noise velocity space model (an Ornstein-Uhlenbeck process) by comparing the simulated long-time diffusion rate with the diffusion rate proposed by the theory. We then use the simulated data to calculate the unknown space diffusion coefficients that appear in the reduced position-space Fokker-Planck equation and summarize the results. [Preview Abstract] |
Monday, November 21, 2016 10:53AM - 11:06AM |
H28.00002: Near-wall effects for momentum, heat and mass transport in gas-particle suspensions at moderate Reynolds numbers Stefan Radl, Federico Municchi, Christoph Goniva Understanding transport phenomena in fluid-particle systems is of primary importance for the design of large-scale equipment, e.g., in the chemical industry. Typically, the analysis of such systems is performed by numerically solving a set of partial differential equations modeling the particle phase and the fluid phase as interpenetrating continua. Such models require a number of closure models that are often constructed via spatial filtering of data obtained from particle-resolved direct numerical simulations (PR-DNS). In the present work we make use of PR-DNS to evaluate corrections to existing closure models. Specifically, we aim on accounting for wall effects on the fluid-particle drag force and the particle-individual Nusselt number. We then propose an improved closure model to be used in particle-unresolved Euler-Lagrange (PU-EL) simulations. We demonstrate that such an advanced closure should account for a dimensionless filter size, as well as a normalized distance from the wall. In addition, we make an attempt to model the filtered fluid velocity profile in wall-bounded suspension flows. [Preview Abstract] |
Monday, November 21, 2016 11:06AM - 11:19AM |
H28.00003: Large scale simulation of particle laden flows using surface-resolved unstructured overset meshes Wyatt Horne, Krishnan Mahesh Particle-laden flows often involve a large range of length scales spanning from large convective scales down to scales near that of the length scale of individual particles. Resolving the fluid features at and below that of individual particles for cases with many moving particles presents difficult numerical challenges. We present a method that seeks to simulate such cases for many moving particles (O(100,000) particles) that uses surface-resolved unstructured overset meshes. Details of the method are overviewed including communication strategies, mesh connectivity, particle movement and the base fluid solver. Simulation results are presented from simulations of single moving particles and from large scale particle-resolved direct numerical simulations of many moving particles. [Preview Abstract] |
Monday, November 21, 2016 11:19AM - 11:32AM |
H28.00004: A numerical study of initial-stage interaction between shock and particle curtain Xiaolong Deng, Lingjie Jiang High speed particulate flow appears in many scientific and engineering problems. Wagner et al. 2012 studied the planar shock - particle curtain interaction experimentally, found the movement and expansion of the particle curtain, together with the movement of shock waves. Theofanous et al. 2016 did similar experiments, discovered a time scaling that reveals a universal regime for cloud expansion. In these experiments, both the particle-fluid interaction and the particle-particle collision are not negligible, which make it challenging to be dealt with. This work aims to numerically study and understand this problem. Applying the stratified multiphase model presented by Chang \& Liou 2007 and regarding one phase as solid, following Regele et al. 2014, we study the initial stage of a planar shock impacting on a particle curtain in 2D, in which the particles can be regarded as static so that the collision between particles are not considered. The locations of reflected shock, transmitted shock, and contact discontinuity are examined. The turbulent energy generated in the interacting area is investigated. Keeping the total volume fraction of particles, and changing the particle number, good convergence results are obtained. Effective drag coefficient in 1D model is also calibrated. [Preview Abstract] |
Monday, November 21, 2016 11:32AM - 11:45AM |
H28.00005: Particle-laden turbulence under radiation: toward a novel small-particle solar receiver Ari Frankel, Ali Mani, Gianluca Iaccarino In particle-based solar receivers, an array of mirrors focuses sunlight onto a falling curtain of particles in a duct that absorb the light and warm up. The heated particles can be stored for later energy extraction. In this work we consider a design concept in which the particles and air are in a co-flowing configuration, and as the particles are heated they conduct the energy to the surrounding air. The air-particle mixture can then be separated and the heated air used for energy extraction. To assess the viability of this energy concept we have developed a simulation capability to analyze the flow of small particles in a turbulent flow with radiation. The code combines a point-particle direct numerical simulation of the particle-air flow in the low Mach number limit with the discrete ordinates solution of the gray, quasi-steady radiative transfer equation. We will describe the individual solution components and the coupling methodology. We will then demonstrate some results from the replication of a lab-scale experiment of a laser diode array irradiating a transparent channel with a flowing air-particle mixture. [Preview Abstract] |
Monday, November 21, 2016 11:45AM - 11:58AM |
H28.00006: Radiation Transport Through a Particle Laden Turbulent Flow Hilario Torres, Gianluca Iaccarino Direct numerical simulations of a turbulent duct flow laden with small particles was performed at several Reynolds and Stokes numbers. After the flow reached a statistically stationary state the instantaneous particle positions were saved at several time steps. Separate radiative heat transfer calculations were performed to study the amount of absorbed radiation and the local heat flux. The radiative source was considered outside of the duct, and one wall contained a window from which thermal radiation streamed through. The fluid was treated as transparent and the instantaneous particle positions obtained from the DNS where used to build Eulerian absorption and scattering fields. A Monte Carlo ray tracing code has been developed and used to solve for the radiative intensity, incident radiation, and heat flux inside of the domain. The qualitative behavior of the radiation fields as the particle positions change due to the turbulence are discussed. The effects of changes in the resolution of the Eulerian mesh used to convert the Lagrangian particles into absorption and scattering fields are also presented. The sensitivity of the amount of total absorbed radiation in the domain is also discussed in both of the previously mentioned cases. [Preview Abstract] |
Monday, November 21, 2016 11:58AM - 12:11PM |
H28.00007: Laser Induced Dual Fluorescence Ratiometric Technique for Mixing Characterization in Microfluidic Systems David Bedding, Carlso Hidrovo Increasing the rate of mixing within microfluidic systems is vitally important in understanding biological and chemical reaction kinetics and mechanisms.~ The small length scales characteristic of these systems which translate into highly viscous, Stokes flows result in mixing that is primarily dominated by diffusion.~ In order to counteract this, an approach that utilizes inertial droplet collisions to promote chaotic advection between two mixing species has been developed.~ A Laser-Induced Dual Fluorescence (LIDF) system in conjunction with a high-speed camera and appropriate optics are used to capture two intensity fields providing information about the mixing process as well as the excitation intensity field over the volume of interest. The rate of mixing for the coalescing droplets was quantified by taking the standard deviation of the first intensity field over time, while the second intensity field provides information about the intensity field.~A~ratiometric imaging approach allows removal of mixing fluorescence signal noise in the form of variation in excitation intensity, primarily from the lasing patterns and lensing effects within the interrogation volume. [Preview Abstract] |
Monday, November 21, 2016 12:11PM - 12:24PM |
H28.00008: Impact of nongray multiphase radiation in pulverized coal combustion Somesh Roy, Bifen Wu, Michael Modest, Xinyu Zhao Detailed modeling of radiation is important for accurate modeling of pulverized coal combustion. Because of high temperature and optical properties, radiative heat transfer from coal particles is often more dominant than convective heat transfer. In this work a multiphase photon Monte Carlo radiation solver is used to investigate and to quantify the effect of nongray radiation in a laboratory-scale pulverized coal flame. The nongray radiative properties of carrier phase (gas) is modeled using HITEMP database. Three major species -- CO, CO$_2$, and H$_2$O -- are treated as participating gases. Two optical models are used to evaluate radiative properties of coal particles: a formulation based on the large particle limit and a size-dependent correlation. Effect of scattering due to coal particle is also investigated using both isotropic scattering and anisotropic scattering using a Henyey-Greenstein function. Lastly, since the optical properties of ash is very different from that of coal, the effect of ash content on the radiative properties of coal particle is examined. [Preview Abstract] |
Monday, November 21, 2016 12:24PM - 12:37PM |
H28.00009: Transport of inertial anisotropic particles under surface gravity waves Michelle DiBenedetto, Jeffrey Koseff, Nicholas Ouellette The motion of neutrally and almost-neutrally buoyant particles under surface gravity waves is relevant to the transport of microplastic debris and other small particulates in the ocean. Consequently, a number of studies have looked at the transport of spherical particles or mobile plankton in these conditions. However, the effects of particle-shape anisotropy on the trajectories and behavior of irregularly shaped particles in this type of oscillatory flow are still relatively unknown. To better understand these issues, we created an idealized numerical model which simulates the three-dimensional behavior of anisotropic spheroids in flow described by Airy wave theory. The particle’s response is calculated using a simplified Maxey-Riley equation coupled with Jeffery’s equation for particle rotation. We show that the particle dynamics are strongly dependent on their initial conditions and shape, with some some additional dependence on Stokes number. [Preview Abstract] |
Monday, November 21, 2016 12:37PM - 12:50PM |
H28.00010: Internal Combustion Engines as Fluidized Bed Reactors Zoe Lavich, Zachary Taie, Shyam Menon, Walter Beckwith, Shane Daly, Devin Halliday, Christopher Hagen Using an internal combustion engine as a chemical reactor could provide high throughput, high chemical conversion efficiency, and reactant/product handling benefits. For processes requiring a solid catalyst, the ability to develop a fluidized bed within the engine cylinder would allow efficient processing of large volumes of fluid. This work examines the fluidization behavior of particles in a cylinder of an internal combustion engine at various engine speeds. For 40 micron silica gel particles in a modified Megatech Mark III transparent combustion engine, calculations indicate that a maximum engine speed of about 60.8 RPM would result in fluidization. At higher speeds, the fluidization behavior is expected to deteriorate. Experiments gave qualitative confirmation of the analytical predictions, as a speed of 48 RPM resulted in fluidized behavior, while a speed of 171 RPM did not. The investigation shows that under certain conditions a fluidized bed can be obtained within an engine cylinder. [Preview Abstract] |
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