Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session G37: Particle Laden Flows |
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Chair: Ellen Longmire, University of Minnesota, Twin Cities Room: 619 |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G37.00001: Transport and Deposit Structure for Particle-laden Binary Rivulets Aref Ghafouri, Timothy Singler, Xin Yong, Paul Chiarot We report on the use of inkjet printing to produce rivulets of particle-laden water-alcohol binary solutions. Our goal was to elucidate the transport and deposit structure of the particles dispersed in the rivulet for varying alcohol content. The rivulets were printed on glass substrates that were chemically treated to ensure the contact line remained pinned during evaporation, which inhibited the breakup of the rivulet due to the Rayleigh-Plateau instability. Fluorescent nanoparticles were used as tracers to reveal the flow field during and after inkjet printing. For pure aqueous solutions, only an axially-directed flow was established along the rivulet. The addition of ethanol to the ink induced a strong Marangoni effect in the transverse direction during evaporation. When combined with the axial flow, this solutal Marangoni convection produced a helically-shaped flow along the axis of the rivulet. The significantly lower surface tension of ethanol compared to water also caused a decrease in the contact angle, which increased the wetted area of the rivulet and further altered the particle transport and deposit structure. [Preview Abstract] |
Sunday, November 24, 2019 4:01PM - 4:14PM |
G37.00002: Effect of turbulent puffs on the Segr\'{e}-Silberberg effect in particulate pipe flow Sagnik Paul, Ellen Longmire Particles in laminar pipe flow tend to accumulate at a certain radius close to the wall. When the flow becomes unstable such that turbulent puffs occur, the puffs can disturb the accumulation of particles. In the current work, we investigate the behavior of polystyrene beads in a neutrally buoyant liquid ($\rho =$1046 kg-m-3) over pipe Reynolds numbers in the laminar and transitional range. In our setup, we observe discrete puffs between Re$=$2100 and 2600 and study the distribution of particles versus radius. The transition Reynolds number and particle distribution are expected to be dependent on the ratio of the particle diameter (d) to pipe diameter (D), and the particle volume fraction ($\phi )$. Particle distributions and motions are observed in planes aligned parallel and perpendicular to the pipe axis using both LED and laser sheet imaging. Images are analyzed to quantify particle position distributions. In laminar flow with D/d$=$43 and $\phi =$0.005, the maximum concentration of particles occurs at 0.44D. In transitional flow at higher Re, the puffs exhibit strong disturbances near the walls that disrupt the local particle accumulation. The effect and relative importance of these disturbances on particle concentration and velocity will be discussed. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G37.00003: Experimental investigation of particle-laden under-expanded jets Taehoon Kim, Rui Ni, Jesse Capecelatro, Yuan Yao, Gregory Shallcross, Manish Mehta, Jason Rabinovitch We present an experimental investigation of particle dynamics in sonic under-expanded jets. In this study, the mass loading and particle slip velocity are independently controlled by using a particle injector and a particle accelerator, which are integrated together in a hopper-style particle feeding system. An ultra-high-speed Schlieren imaging and a particle tracking system operating at 2-5 million fps were employed to acquire the dynamics of both the gas phase and particle phase. Statistics for both particle-free and particle-laden under-expanded jets in the near field will be discussed. These new results will provide a rich dataset for expanding our knowledge in compressible multiphase flow problems as well as validating models and simulations in this regime. [Preview Abstract] |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G37.00004: Polydisperse Droplet Size Growth in a Turbulent Air Flow - Effects of Droplet Number Density and Size SHYAM KUMAR M, S.R CHAKRAVARTHY, MANIKANDAN MATHUR Interaction of polydisperse droplets in a turbulent air flow features prominently in a wide range of phenomena. Here, we present an experimental study on the collective effects of droplet number density ($ND$) and mean droplet size ($D_{10}$) on the droplet size growth. For each ($ND, D_{10}$), we observe an optimum turbulent intensity and a corresponding maximum droplet size growth rate $R^*$. Interestingly, an increase (decrease) in $ND (D_{10})$ doesn't influence $R^*$ up to some threshold values of $ND$ and $D_{10}$, beyond which a sudden increase in $R^*$ is observed. The observed trend is understood in terms of droplet pair dispersion, as observed from Long Distance Microscopy images. The dispersion of droplet pairs is negligible till the threshold conditions are reached. Surprisingly, a substantial increase in dispersion is observed beyond the threshold values, which potentially increases the collision probability, and hence $R^*$. The opposing effects of $ND$ and $D_{10}$ on collision rates cause a negligible variation of $R^*$ up to the threshold values; however, the effect of $ND$ overrides the effect of $D_{10}$ beyond the threshold values, and hence causes a sudden increase in $R ^*$. [Preview Abstract] |
Sunday, November 24, 2019 4:40PM - 4:53PM |
G37.00005: Multi-scale characterization of the effect of gas swirl on two-fluid coaxial atomization. Nathanael Machicoane, Peter D. Huck, Timothy B. Morgan, Julie K. Bothell, Rodrigo Osuna-Orozco, Danyu Li, Theodore J. Heindel, Alan L. Kastengren, Alberto Aliseda This work aims at developing a better mechanistic understanding of the processes that control droplet formation and transport in coaxial two-fluid atomization. The goal is to experimentally develop spray control strategies and implement feedback control of the spray characteristics. We will present results on the impact of modulation of the swirl ratio (ratio of gas flow rate with tangential momentum to the total gas flow rate) on the physics of the atomization, from the formation of liquid ligaments close to the nozzle, to droplet size and spatiotemporal distributions in the mid-field. This parameter dominates the spray structure when it is above a critical value and its modulation in time has a non-linear effect on the spray dynamics that can be used to shape it towards a desired state (the control goal). Synchrotron X-ray measurements provide detailed information of the spray near-field, while time-resolved optical measurements of the spray structure, as well as the droplet size and velocity, are collected in the mid field. The response of the spray to the open-loop actuations is mapped from these measurements. This is used to develop reduced order model for feedback control and to validate assumptions used for computational, adjoint-based, control strategies. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G37.00006: Dynamics of turbidity currents: Ambient fluid entrainment and basal drag Jorge Salinas, Mrugesh Shringarpure, Mariano Cantero, S. Balachandar Turbidity currents are sediment laden flows that run along inclined or horizontal surfaces. They are driven by the excess hydrostatic pressure resulted from the density difference between the current carrying sediment and the clear ambient fluid. The amount of particles carried is influenced by the strong coupling between turbulence and suspended sediment. In this work we perform direct numerical simulations (DNS) of spatially evolving, spanwise- homogeneous turbidity currents. We focus our attention on the process of entrainment of clear ambient fluid that happens at the interface between the current and the ambient layer. Moreover, the study of basal drag is performed. Turbidity currents have been studied in the past by means of layer-averaged equation models, which make use of several closure models. Two of these models are the entrainment assumption and the basal drag model. In this work we analyze the dependence of these models with the flow parameters (bulk Richardson and Reynolds numbers) together with the settling velocity of the sediment. We pay attention to the regime where the bulk properties of the flow vary slowly, called normal condition. Furthermore, we analyze the effect of acceleration/deceleration of the flow away from normal condition. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G37.00007: Particle-laden upward jet in a crossflow: particle dispersion and tracking of particle source Jooyeon Park, Hyungmin Park We experimentally investigate the particle dispersion due to the vortical interaction in the particle-laden upward jet with a crossflow focusing on a large scale phenomena in multiple planes. We vary the velocity ratio (R) between the jet and crossflow, which is classified into three regimes of no crossflow, 3.0 -- 3.5 and 1.0 -- 1.2. As a dispersed phase, we use Silicon particles (6 -- 205 um in size) and the corresponding Stokes number is in the range of St $=$ 0.01 -- 27.42. For each case, the air flow and particle velocities are measured by PIV, and the particle distribution is obtained by planar nephelometry. For lower R, due to stronger counter-rotating vortex pairs (CVPs) in a continuous phase, drag force on particles become dominant so that the particles are swept from the jet center near the jet exit for St \textless \textless 1, but for St \textgreater \textgreater 1, the particles tend to travel along the jet center regardless of vortical effects. Interestingly, only for St $=$ 1 (irrespective of R), the particles agglomerate along the jet center before the CVP collapses. Finally, based on these observations, a 3D dispersion model is developed, which is used for the estimation of particle source location and validated with the experimental data. [Preview Abstract] |
Sunday, November 24, 2019 5:19PM - 5:32PM |
G37.00008: Physical origins of the dependence of drag force on density ratio through fully-resolved direct numerical simulation of particle-laden to bubbly flow Vahid Tavanashad, Shankar Subramaniam The objective of this study is to understand the dynamics of freely evolving particle suspensions over a wide range of particle to fluid density ratios, from solid particles in a gas (high density ratio) to bubbles in a liquid (low density ratio). The dynamics of particle suspensions are characterized by the average momentum equation, where the dominant contribution to average interphase momentum transfer is the mean drag force. The mean drag is characterized using fully-resolved simulation over a wide range of density ratios in a canonical problem: a statistically homogeneous suspension where a steady mean slip velocity between the phases is established by an imposed mean pressure gradient. We explain the change of mean drag of freely evolving particle suspensions with reference to a fixed bed by considering the emergence of spatial structure in the particle configuration, effect of particle velocity fluctuations, and the mobility of particles. These considerations could be used to develop a physics-based drag law for dispersed multiphase flows. The study of the fluctuations of the drag force on individual particles about the mean drag shows that the force distribution follows a normal distribution with a variance from the mean drag that decreases with decreasing density ratio. [Preview Abstract] |
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