Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session X07: Multiphase Flows: ParticleLaden Flows (10:45am  11:30am CST)Interactive On Demand

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X07.00001: Experimentallyguided inflow conditions for EulerLagrange Large Eddy Simulations of Midfield Spray Kai Liu, Peter Huck, Alberto Aliseda, Sivaramakrishnan Balachandar The coaxial round jet sprays are common in a variety of engineering applications. The spray is commonly analyzed separately as two parts, a surface tension dominated nearfield where the intact liquid ejected from the nozzle deforms and atomizes, and a fullydisperse midfield where the liquid phase has already broken into tiny droplets that continue to drift as a polydisperse distribution of droplets. The midfield spray can be efficiently simulated by the EulerLagrange approach. However, how to model the inflow condition of the droplets is of great difficulty. Based on companion experimental measurements, this work has rigorously analyzed the droplet position, diameter and velocity statistics, as well as their correlations, and accordingly developed a highfidelity stochastic injection model for use in the EulerLagrange simulations. The gas phase at Reynolds number 50000 is solved by twoway coupled large eddy simulations and validated against experimental measurements from the first to the third order turbulent statistics. When injected according to the injection model, the twophase simulation results yield consistent timeaveraged results with the experimental data gathered at downstream locations. [Preview Abstract] 

X07.00002: Experimental Investigation of TwoWay Coupling in ParticleLaden Compressible Flows Juan Sebastian Rubio, Meet Patel, Jesse Capecelatro, Jason Rabinovitch, Rui Ni It is well known that, for particleladen flows, increasing the particle volume fraction $\phi_v$ and mass loading $\phi_m$, defined as the ratio of the specific masses of the particle and fluid phases, switches the dispersed phase from passively responding to the carrier phase (oneway coupling) to actively modulating surrounding flows (twoway coupling). However, it is still largely unknown how this twoway coupling could manifest in the compressible regime where the particlegas slip velocity could reach from transonic to supersonic speeds. In the present study, twoway coupling effects in compressible flows are investigated via ultrahighspeed particle tracking of an underexpanded sonic jet seeded with inertial particles. The emergence of bow shocks around individual particles significantly modulates the Mach disk location and fluctuation. This may provide new insights in the modeling of twoway coupling. The experimental results in this study are compared with the numerical simulations performed at the University of Michigan. Further details are found in the companion presentation titled, ``Numerical Simulation of ParticleLaden Underexpanded Jets." [Preview Abstract] 

X07.00003: Numerical Simulation of ParticleLaden Underexpanded Jets Meet Patel, Juan Sebastian Rubio, Rui Ni, Jason Rabinovitch, Jesse Capecelatro Numerical simulations of inertial particles in underexpanded jets are performed to isolate gas phase compressibility effects on particle velocity statistics. Highspeed compressible particleladen flows can be observed in a number of practical applications, from the interaction of rocket exhaust plumes with planetary and lunar surfaces to coal dust explosions. Unlike lowspeed gassolid flows where unsteady forces acting on particles can be neglected due to the large density ratio, in the highspeed flows considered here such forces can have orderone effects due to large relative acceleration between the phases. The focus of present work is to assess the ability of existing drag laws to reproduce velocity statistics in a three dimensional EulerianLagrangian framework. The gasphase equations are solved using a class of highorder, energystable finite difference operators, and a nozzle geometry is modeled using a ghostpoint/directforcing immersed boundary method. We also present effects of twoway coupling on the structure of the jet. Results are compared with experiments performed at Johns Hopkins University. Further details on the experiments can be found in our companion presentation, ''Experimental Investigation of TwoWay Coupling in ParticleLaden Compressible Flows". [Preview Abstract] 

X07.00004: Disruption and Recovery of Tubular Pinch Effect in Transitional ParticleLaden Pipe Flow Sagnik Paul, Ellen Longmire In laminar pipe flow, neutrally buoyant particles concentrate at a specific radius near the wall. This Tubular Pinch Effect, first studied by Segre and Silberberg, is related to migration induced by inertia.~The critical Reynolds number and radius~of peak concentration~are dependent on the ratio of pipe to particle diameter (D/d), and the volume fraction of the particles ($\phi )$.~During laminar to turbulent transition, this accumulation of particles is disturbed by puffs. In the current study, we examine the behavior of polystyrene beads in a 20{\%} glycerolwater solution ($\rho =$1046 kgm$^{\mathrm{3}})$ as they interact with isolated puffs.~~Experiments are performed with D/d $=$43 {\&} 129 and $\phi =$0.005 {\&} 0.01.~~Planar imaging is employed with a backlit LED panel and a DSLR camera. PTV is used to determine the velocities of the particles.~For D/d$=$43 and $\phi =$0.005, we find the radial peak concentration at 0.85R. We also find that the~local~accumulation of particles is disrupted, and radial velocities become significant with the puff.~Puff effects on temporal and radial variations of particle concentration, along with the effects on particle velocities will be discussed. We will also discuss the time required for particles to recover to their undisturbed annular arrangement. [Preview Abstract] 

X07.00005: Simulations of AirShock Driven Particle Jetting in a Dense Particle Bed. Rahul Babu Koneru, Bertrand Rollin, Bradford Durant, Frederick Ouellet, S. Balachandar In this work, simulations of highspeed dispersal of a dense particle bed are carried out to investigate the underlying mechanisms responsible for the formation of the jetlike structures. To this end, fourway coupled EulerLagrange (EL) simulations of an airshock interacting with a dense particle bed are carried out. The simulations are carried out using a discontinuous Galerkin spectral element solver coupled with a highorder Lagrangian solver. A discrete element method is used to resolve the particle collisions along the normal direction. Parametric studies are carried out to test the effect of the incident shock strength and the coefficient of restitution on the development of the jetlike structures. The channeling of the particles is observed to be related to vorticity deposition at the outer edge of the particle bed consistent with the multiphase analog of the RichtmyerMeshkov instability. Additionally, the role of vorticity generated due to the force coupled back to the gas is investigated by analyzing the relaxation of the relative velocity between both the phases. [Preview Abstract] 

X07.00006: Inertial focusing patterns and their transition for a neutrally buoyant sphere suspended in rectangular duct flow Hiroshi Yamashita, Masako SugiharaSeki Spheres suspended in rectangular duct flow are known to cross streamlines due to the inertial lift force and focus at certain points in the downstream crosssection. Recent studies have shown the appearance of various focusing points, depending on the aspect ratio of the crosssection ($A)$, the blockage ratio of the sphere to the duct ($\beta )$, and the Reynolds number (Re). Representative focusing patterns for spherical particles in rectangular duct flow are that the particles focus only near the center of the long side (pattern (a)) and near both the centers of its short and long sides (pattern (b)). In this study, we have aimed at elucidating the focusing patterns and their transition appeared in suspension flow through rectangular ducts, by a numerical simulation. We calculated the map of the inertial lift force over the crosssection and estimated the focusing positions and the particle trajectories. We have found that, for $A=$2 and $\beta =\sim $0.3, an increase in Re from 100 to 300 induced the transition of the focusing pattern from (a) to (b). By capturing changes of the nullclines for the particle trajectories, we explained this transition as the bifurcation phenomena in terms of the particle equilibrium positions. [Preview Abstract] 

X07.00007: Paths to caustic formation in turbulent aerosols Jan Meibohm, Vikash Pandey, Akshay Bhatnagar, Kristian Gustavsson, Dhrubaditya Mitra, Prasad Perlekar, Bernhard Mehlig The dynamics of identical, small, and heavy particles in a turbulent flow has singularities, socalled caustics. At a caustic, local particle neighbourhoods collapse as the phasespace manifold folds over configuration space and particlevelocity gradients diverge. The formation of caustics has been studied in detail in the whitenoise limit where caustic formation is essentially Kramers' escape. A different picture is that of the sling effect, where caustics form as the inertial particles are expelled from vortices in the turbulent flow. Here we reconcile these two distinct perspectives by computing an optimal escape path for the matrix of particlevelocity gradients in a persistentflow model that accounts for persistent vortices in the flow. Whether caustics form by Kramers' escape or according to the sling effect depends on the degree of particle inertia. We compare our predictions with statisticalmodel simulations, and with results based on direct numerical simulations of twodimensional turbulence. [Preview Abstract] 

X07.00008: Experimental investigation on dynamics of charged inertial particles in turbulence Xuan Ruan, Matt Gorman, Rui Ni We present an experimental study on interaction between turbulence with triboelectricallycharged particles in a twostage apparatus. In this study, bidisperse spherical particles are first charged by an upward jet in a highpressure capsule. During this process, particles undergo frequent collisions and gain sufficient charges. By suddenly discharge the gassolid mixture into a lowerpressure environment, an energetic particleladen turbulent jet flow is generated, and their dynamics are tracked by our inhouse particle tracking system to determine the particleparticle interaction. Furthermore, the charge distribution as a function of particle size are measured by a Faraday cage. Through systematic experiments, the effects of ambient conditions and particle parameters on particleparticle interaction and particleturbulence interaction are discussed in detail. This study will unveil the complex coupling between charged particles and turbulence. [Preview Abstract] 

X07.00009: Indoor particulates removal using water microdroplets based on wet scrubbing method Jeongju Kim, Jeong Jae Kim, Sang Joon Lee Particulate matter (PM) is microscopic particles suspended in the air. PM has a lot of adverse effects on human. Therefore, various studies have been conducted to reduce PM, but an outstanding method has not been introduced. The wet scrubbing, which is one of the existing methods for remove PM, has a disadvantage that fine PM (PM$_{\mathrm{2.5}})$ removal efficiency is rapidly reduced compared with PM$_{\mathrm{10}}$. In this study, we experimentally investigated PM removal effect by water microdroplets based on the wet scrubbing method and observed temporal variations of PM concentration in a test chamber. When the microdroplets were sprayed, the removal effect of PM concentration increased with time, and PM removal efficiency and deposition constant were calculated. The experimental results were compared with analytical results based on semiempirical models proposed by previous studies. To analyze the models, PIV technique was utilized to obtain the flow velocity around the outlet. The experimental results showed higher performance compared with both the previous results of wet scrubbing and the analytical results. These results suppose that microdroplets sprayed into an indoor space helps to decrease PM, and PM$_{\mathrm{2.5}}$ more effectively. [Preview Abstract] 

X07.00010: Anisotropy and NonMaxwellian behavior of particle velocity fluctuations in circulating fluidized beds Cheng Li, Avinash Vaidheeswaran, Balaji Gopalan, Xiongjun Wu, Rowan Steven, Bryan Hughes, William A. Rogers This study focuses on comparing the distribution of fluctuation velocity of solid particles in the circulating fluidzed bed (CFB). Experiments have been conducted in two CFBs with one order of magnitude difference in size but similar superficial gas velocity. The labscale system uses Zeolite particles with a mean diameter of 793 micron, which are tracked using digital inline holography (DIH) in the standpipe region of the bed. Additionally, 10  40 micron fine particles presumably resulting from attrition are detected and tracked as well. In the industrialscale system, 81 micron mean diameter fluid catalytic cracking (FCC) particles are tracked at multiple radial locations in the riser section using a borescope. Results highlight the anisotropy and nonMaxwellian distribution of velocity fluctuations due to Levy flight of particles stemming from complex interparticle and interphase interactions. Furthermore, the transverse component exhibits symmetry while streamwise component is asymmetric in both the systems. [Preview Abstract] 

X07.00011: Numerical Investigation of Explosive Particle Jetting Calvin Young, Jonathan Regele, Yash Mehta, Jacob McFarland A blast wave traveling through a region of particulate matter has been observed to produce distinct clusters and jets of particles expanding with the flow. This phenomenon has yet to be fully explained, and as such particle interaction models may be improved upon by further numerical investigation. A series of 2D simulations using the adaptivewavelet compressible flow code AWESUMM are performed in order to investigate this phenomenon qualitatively. Particles in this code are modeled as fully resolved cylinders via a volume penalization method. Phase interactions are captured by twoway particlegas coupling and particleparticle collisions and momentum transfer. In this set of simulations, an incident planar shock is passed through a particle field, and the resulting flow field is allowed to evolve. Particle fields are varied in initial distribution in area fraction along the height of the domain, and in coefficient of restitution between particles. Particle trajectories and field area fractions are used to characterize evolution of the system over time. Further work will serve to shed more light on the mechanisms of jetting and validate particle models in use with other applications. LAUR2025844 [Preview Abstract] 

X07.00012: The Role of Interfacial Materials in Wetting Phase Drainage from DeadEnd Pores Mario Cordova Gonzalez, Hossein Hejazi Immiscible displacement in porous media is found in many engineering and natural processes including oil production from underground reservoirs. Mobilization of a trapped fluid from cavitylike configurations in porous rocks is minimized due to geometrical restriction. The addition of interfacial materials in the form of colloidal particles in the main flow stream may generate interfacial inhomogeneities and accelerate the residual fluid motion. We present a scenario in which suspended particles in a carrier solution bypass a series of saturated cavities. We employ microfluidic chips consisting of deadend pores connected to a main channel. We use mineral oil as the wetting phase and dispersions of silica nanoparticles as the displacing fluids. We capture 3D images of the wetting phase drainage from the cavity space using confocal laser microscopy and track the velocity field on the trapped fluid using a microPIV system. The rate of the meniscus invasion inside the cavity is considerably altered in the presence of surfaceactive particles where the oil mobilization could be related to the spontaneous emulsification at the imposed shear rate. Understanding different mechanisms yielding motion of a stagnant phase is critical in many fluid displacement systems. [Preview Abstract] 

X07.00013: The effect of laserinduced breakdown on particle dispersion Kyuho Han, Sungkyun Oh, Hyungrok Do, Wontae Hwang Being able to modify particle or droplet dispersion can have a significant impact for various industrial applications, such as electrostatic precipitators or combustor fuels sprays. Although it is feasible to control global particle distributions by changing overall flow conditions, it is challenging to locally control particle distributions. In this study, we investigated the feasibility of utilizing laserinduced breakdown (LIB) for controlling local particle distributions. LIB initially creates a shockwave, and subsequently induces a hotgas vortex at the laser focal point. A particle cavity (i.e. void region) is created by the shockwave, and it evolves over time due to the hotgas vortex, in three temporal phases. We have conducted experiments for three different cases of breakdown energy, and analyzed the area and lifespan of the cavity. It is shown that LIB can be utilized as a fast and nonintrusive technique to control local particle dispersion. [Preview Abstract] 

X07.00014: Motion and Instability Properties of LambOseen Vortex in ParticleLaden Flows shuai shuai, Anubhab Roy, M.Houssem Kasbaoui We investigate the destabilization of a LambOseen vortex by dispersed inertial particles in EulerianLagrangian simulations. We study the LambOseen vortex as presentative flow for the swirling motion of a vortex. The LambOseen vortex is an extremely resilient structure of singlephase flows, a property that falls from its proven hydrodynamic stability to 2D modal perturbations. Remarkably, we show that dispersing inertial pointparticles triggers a novel instability, characterized by (1) rapid attenuation of the carrier flow vorticity at the core, (2) a structure of the flow vorticity field dominated by spiral fringes, (3) faster growth of the vortex size than in singlephase flows, and (4) transient growth ending when all particles have been ejected out of the vortex core. The simulations show the existence of the instability for a wide range of particle Stokes numbers (0.1 – 1.0) and mass loadings (0.1 – 2.0). Analyzing the perturbation growth rates, we show that the instability modes depend on the mass loading from $0.5 \sim 1.0$, and propose new scaling laws for the vorticity decay rate and radius growth rate that depend on the particle Stokes number. [Preview Abstract] 
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