Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session Q08: Multiphase Flows: ParticleLaden Flows II 
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Chair: Alberto Aliseda, University of Washington Room: Georgia World Congress Center B213 
Tuesday, November 20, 2018 12:50PM  1:03PM 
Q08.00001: Flexible fibers in turbulent channel flow Diego Dotto, Cristian Marchioli In this paper we investigate the dynamics of small flexible fibers in turbulent channel flow. We aim at examining the translational and rotational behavior of fibers with different elongation (parameterized by the aspect ratio) and inertia (parameterized by the Stokes number) with and without fiberfluid coupling. We use a EulerianLagrangian approach based on direct numerical simulation of turbulence to describe fiber dynamics. Fibers, which are longer than the Kolmogorov length scale, are modelled as chains of subKolmogorov rods connected through ballandsocket joints that enable bending and twisting. Different mass and volume fractions are considered to investigate twoway coupling effects. Velocity, orientation and concentration statistics, extracted from simulations at shear Reynolds number Re_{τ}=300 are presented to give insights into the complex fibersturbulence interactions that arise when nonsphericity and deformability add to fiber inertia. Flexible fibers in the dilute regime appear to undergo the same inertiadriven mechanisms that govern preferential concentration of spherical particles in bounded flows. We show that momentum coupling provides an additional bias, which may produce significant quantitative modifications in the statistics of both phases. 
Tuesday, November 20, 2018 1:03PM  1:16PM 
Q08.00002: The effect of the particle mass loading in particle dispersed multiphase turbulence channel flow Tian Zhou, Chunxiao Xu, Weixi Huang, Lihao Zhao In particle dispersed multiphase channel flow, the interaction between particles and fluid is extremely complex. Many factors such as particle size, particle density, Stokes number and particle mass loading play assignable role in modulation of the flow statistics and coherent structure. The effect of the particle mass loading has been explored in twoway coupled direct numerical simulations of turbulent channel flow. Some fluid statistics such as streamwise Reynolds stress show nonmonotonicity with particle mass loading increasing. Two main mechanisms account for the phenomenon: More particles means stronger interaction between particles and fluid; With particle mass loading increasing, the characteristic time scale of the fluid increases, which means the Stokes number of the particles decreases , the particles become “lighter” and weaken the effect of the particles. 
Tuesday, November 20, 2018 1:16PM  1:29PM 
Q08.00003: Flow of large particles through straight and bifurcating pipe flow  experimental study Martin Leskovec, Siye Song, Fredrik Lundell Predicting and modelling multiphase flows with high accuracy is of high relevance in many industrial processes. Flow predictions may lead to reduced energy usage, hardware investments and raw material usage and also an increased product quality. Access to experimental results are necessary in order to develop Computational Fluid Dynamics (CFD) models for multiphase flows. An interesting flow case is the flow of relatively large particles (d_{p }/ D = 0.2  0.4, where d_{p} is particle size and D pipe diameter) through straight and bifurcating pipe flow. Experiments in laminar and turbulent flow at different Stokes numbers (1  300) and particle to fluid density ratios (0.9  1.2) are conducted. Spherical and cubical particles have been compared at volume fractions 5  30%. Measurements are performed in a circulating loop and results include pressure drop and velocimetry for the straight pipe flow and particle and fluid distribution in the different branches for the bifurcated flow. Velocity and turbulence statistics are measured using Magnetic Resonance Velocimetry (MRV). Differences between spherical and cubical particles are reported and show under what circumstances it becomes critical to include particle shape in CFD modelling. 
Tuesday, November 20, 2018 1:29PM  1:42PM 
Q08.00004: Inertial migration of neutrally buoyant particles in 2D periodic Poiseuille flow with a wide range of particle concentration Wenwei Liu, Chuanyu Wu We present a numerical study on the inertial migration of neutrally buoyant particles in 2D periodic Poiseuille flow using a singlerelaxationtime lattice Boltzmann method coupled with discrete element method, in which the Hertz contact theory is used to model particleparticle interactions. The channel Reynolds number varies in the range Re=4~100 and the channeltoparticle size ratio is set as 16.67 and 8.33. We examine the effects of particle concentration by increasing the solid fraction from 0 to 50%. The tubular pinch effect (or SegréSilberberg effect) is observed in our simulations, which agrees quantitatively with the previous experimental and theoretical results. However, as the particle concentration exceeds a certain limit, the particle inertial focusing becomes inconspicuous. As a consequence, a criterion is proposed to distinguish the focusing/nonfocusing phenomenon, which depends on the channel Reynolds number, channeltoparticle size ratio, as well as the particle volume fraction. 
Tuesday, November 20, 2018 1:42PM  1:55PM 
Q08.00005: Particleladen exchange flows in inclined pipes Nima Mirzaeian, Kamran Alba The buoyancydriven lockexchange flow of a suspension mixture and a pure fluid in inclined pipes is studied experimentally. We Investigate the interpenetration of the heavy particleladen fluid and the light pure fluid in Boussinesq limit while considering the effects of the initial volume fraction of particles φ_{0} and inclination angle of pipe β on the flow. Three distinct regimes are identified: I) Sedimentary: at nearhorizontal inclinations and for φ_{0 }close to dilute and packed limits, the flow comes to a halt as particles settle out of the mixture. II) Mixing: away from the horizontal angle and for the intermediate volume fraction of particles, flow advances steadily and particles stay mixed within the suspension. III) Transitionary: a novel nonlinear and unsteady behavior occurs as flow transitions from sedimentary to mixing regime. Through a scaling analysis, It is revealed that enhanced convection of heavy and light mixtures in inclined pipes (Boycott effect) facilitates the streamwise advancement rate of the particleladen front V_{f} of order cosβ^{2}. Furthermore, the impact of particle size and fluid's viscosity on the classified flow regimes is studied in detail. 
Tuesday, November 20, 2018 1:55PM  2:08PM 
Q08.00006: Effects of Particle Loading on Turbulent Flow in a 90° Elbow Andrew Bluestein, Douglas Bohl Introducing a second phase into a turbulent flow changes its complex nature by modifying the turbulent fluctuations. Experimental data at high volume concentrations are limited due to the presence of the particles which degrade optical clarity. Optical clarity can be restored using refractive index matching (RIM) where the refractive indices of the secondary and continuous phases are matched. In this work, super absorbent hydrogel particles were used to create an index matched system. These particles absorb up to 500x their weight in water, and are therefore inherently index matched and neutrally buoyant. Turbulent flows at Re=11,500 and 115,000 through a sharp edged 90° elbow were studied using PIV. Mean and fluctuating (rms) velocities were measured in the presence of 0 to 5% of hydrogel particles. The results showed little variation due to the presence of the particles. These results are put into context by discussing the parameters used to predict turbulence modulation, most of which predicted attenuation of the rms velocities. A possible explanation for the observed behavior was the low values for the ratio of the slip velocity between the phases to the mean fluid velocity which has been shown to affect turbulence modulation in prior work. 
Tuesday, November 20, 2018 2:08PM  2:21PM 
Q08.00007: Effect of Reynolds number and system size on turbulence modification in particleladen channel flow Naveen Rohilla, Partha S. Goswami Turbulent particleladen flows find many applications, starting from pneumatic transport of solid to separation of particulate from industrial exhaust. The presence of particles in particleladen turbulent flows can augment or attenuate the turbulence level of the gas phase. Earlier studies have shown that modification of turbulence intensity varies with mass loading, Stokes number, Reynolds number and ratio of channel width to particle diameter (L/dp) [Tanaka and Eaton, PRL, 2008]. The phenomenon of turbulent modulation is complex and cannot be defined with a single parameter. Coupled LESDEM simulations have been carried out for different volume fractions and Reynolds numbers with different L/dp ratios to investigate the turbulence modulation in the gas phase. In the present work, we have quantified the effect of L/dp and channel Reynolds number on discontinuous attenuation of turbulence intensity as a function of particle volume loading in a vertical channel flow. It is observed that the extent of attenuation decreases with decrease in L/dp ratio. Also, an increase in Reynolds number subside the phenomena of particleinduced attenuation. 
Tuesday, November 20, 2018 2:21PM  2:34PM 
Q08.00008: Analysis of a SmallScale PulsedFluidized Bed Avinash Vaidheeswaran, Jonathan E Higham, Mehrdad Shahnam Cyclical fluidization of solid particles with a gas phase can produce structured bubbling patterns; these “pulsedfluidized beds” have recently attracted considerable attention due to efficient mixing of particles and their tunability. Previous studies have shown that bubble patterns are controlled by factors including mean velocity at the inlet, pulsing frequency, amplitude of oscillation and bed dimensions. However, experimental investigation of the effect of bubbles on granular rheology is lacking. We present a Particle Tracking Velocimetry study of a quasitwodimensional pulsedfluidized bed. Using a Proper Orthogonal Decomposition, we show that a change in bubble pattern redistributes energy among the superimposed dynamic scales of particlephase motion. Furthermore, we explore the diffusion characteristics of particles using Lagrangian data. Finally, we highlight the predictive capability of EulerianLagrangian simulations using the Discrete Element Modeling code, MFiXDEM. 
Tuesday, November 20, 2018 2:34PM  2:47PM 
Q08.00009: A dynamic spectrallyenriched subgridscale model for preferential concentration of inertial particles in turbulence Maxime Bassenne, Mahdi Esmaily, Perry L Johnson, Daniel Livescu, Parviz Moin, Javier Urzay In this study, a new subgridscale (SGS) model for turbulent velocity fluctuations is proposed for largeeddy simulations (LES) of multiphase flows. The modeled velocity contains scales smaller than the LES grid resolution thereby enabling, in principle, the calculation of smallscale phenomena such as particle preferential concentration and interfacial corrugation dynamics. The deterministic construction of the spectrallyenriched velocity in physical space is based on 1) the modeling of the smallestresolved eddies of sizes comparable to the LES grid size via approximate deconvolution and 2) the reconstruction of SGS fluctuations via nonlinear synthesis of smallscale turbulence. The new model does not contain tunable parameters, can be deployed in nonuniform grids, and is applicable to inhomogeneous flows subject to arbitrary boundary conditions. The performance of the model is assessed in LES of isotropic turbulence laden with inertial particles, where improved agreement with direct numerical simulation results is obtained in the dispersedphase statistics. Application to wallmodeled LES of particleladen channel flow will be presented. 
Tuesday, November 20, 2018 2:47PM  3:00PM 
Q08.00010: Ambient fluid entrainment and basal drag in turbidity currents Jorge Sebastian Salinas, Mrugesh Shringarpure, Mariano Ignacio Cantero, S Balachandar Turbidity current are sediment laden flows that move over inclined or horizontal surfaces. These flows are driven by buoyancy resulting from the density difference between the current carrying sediment and the clear ambient fluid above. A strong coupling between turbulence and suspended sediment particles influences the flow dynamics. Here we focus our attention on the process of ambient fluid entrainment happening at the interface between the current and the deep ambient layer. In this work, we study the dependence of the entrainment coefficient with the bulk Richardson number and the settling velocity of the sediment in the flow. We focus our study on the regime where the bulk properties of the flow vary slowly, usually called normal flow conditions. We employ direct numerical simulations (DNS) of temporally evolving, streamwise spanwise homogeneous turbidity currents. A new model for entrainment is proposed. Furthermore, the dependence of basal drag on Richardson number and settling velocity is analyzed. In addition, the turbulence structures of the flow and its relation to turbulence production and dissipation is studied for both subcritical and supercritical flows. 
Tuesday, November 20, 2018 3:00PM  3:13PM 
Q08.00011: Fully Resolved Simulations of AirShock Interacting with Randomly Distributed Spherical Particles Yash Mehta, Thomas L Jackson, Sivaramakrishnan Balachandar Shock particle interaction is a fundamental problem in many engineering applications, with the dynamics being heavily influenced by the incident shock Mach number and the particle volume fraction. We vary the strength of the incident shock along with the particle volume fraction in order to study the complex wave interaction during shock particle interaction. Mean of flow properties like pressure, density and velocity were computed to characterize the strength of the various waves occurring during shock particle interaction. The random distribution of particles results in velocity and pressure fluctuations. We compute the pseudo turbulent Reynolds stress along with the turbulent kinetic energy to understand their importance during shock particle interaction. <div msbgcolorneutrallighter"="">

Tuesday, November 20, 2018 3:13PM  3:26PM 
Q08.00012: EulerLagrange Simulations of ShockParticle Cloud Interaction Rahul Babu Koneru, Bertrand Rollin, Chanyoung Park, Frederick Ouellet, S Balachandar EulerLagrange (EL) simulations of a shockwave interacting with a cloud of fixed and a cloud of movable particles at various volume fractions (10%30%) and shock Mach numbers (1.223.0) are performed. Results from the particleresolved simulations of fixed particles and experiments performed at the Multiphase Shock Tube (MST) facility at Sandia National Laboratories (SNL) are used to validate the fixed cloud and the moving cloud EL simulations respectively. In the fixed cloud simulations, the effect of the wave drag at supersonic flow Mach numbers is modeled as an inviscid drag. The mean thermodynamic and kinematic gas quantities and the forces experienced by the particles at very short timescales are compared against the particleresolved simulations. In case of the movable particle simulations, the effects of initial particle curtain profile on the particle cloud trajectory is studied. For this, results from a tophat profile and a curve fit (obtained from the experimental data) are compared against the experimental results. 
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