Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session R13: ParticleLaden Flows: ParticleTurbulence Interaction (5:00pm  5:45pm CST)Interactive On Demand

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R13.00001: Numerical modeling of the breakup of cohesive particles by turbulence Yuan Yao, Jesse Capecelatro Micronsized particles in turbulent flows play important roles in many engineering and medical systems such as dust ingestion in gasturbine engines and dry powder inhalers, where particles tend to form aggregates due to interparticle cohesion. The dynamical evolution and morphology of these aggregates involve a complex interplay between turbulent stresses and interparticle cohesive forces. Here we study the turbulenceinduced breakup of a spherical particle `clump' placed in homogeneous isotropic turbulence. Parameters are chosen relevant to powder suspended in air such that cohesion due to van der Waals is important. EulerianLagrangian simulations are performed that models twoway coupling between phases and resolves particleparticle interactions. Aggregate breakup is investigated for different Adhesion numbers, Reynolds numbers and clump sizes. The intermittency of turbulence is found to play a key role on the earlystage breakup process. A scaling analysis shows that the time rate of breakup scales with a turbulent Adhesion number and an aggregate Reynolds number. A phenomenological model of the breakup process is proposed as a granular counterpart to the Taylor Analogy Breakup (TAB) model for droplet breakup, followed by a sensitivity analysis of the model parameters. [Preview Abstract] 

R13.00002: Fluid motion surrounding a lifting sphere in turbulent boundary layers Yi Hui Tee, Ellen Longmire A finitesize sphere with density ratio of 1.006 was released from rest on a smooth wall in turbulent boundary layers with Re$_{\mathrm{\tau }}=$ 680 and 1320 (d$^{\mathrm{+}}=$ 58 and 122). The marked sphere was illuminated with white LEDs and tracked using two pairs of stereoscopic cameras viewing from the side. At the same time, a streamwisespanwise plane of fluid was illuminated by an infrared laser, and fluid motion was captured and tracked with a pair of stereoscopic PIV cameras viewing from the bottom. The 3C sphere translation and rotation were compared with the surrounding fluid motion to understand particleturbulence interactions. Upon release, the sphere accelerated strongly and lifted off of the wall with minimal rotation before eventually descending. It typically collided with and slid along the wall before lifting off again, often reaching greater heights than after the initial liftoff. The sphere streamwise velocity correlated strongly with surrounding fast or slow moving fluid regions. The sphere's spanwise motion, up to 12{\%} of the streamwise distance traveled, often correlated with largescale spanwise fluid motions. In the talk, sphere liftoff will also be discussed in the context of the surrounding fluid motions. [Preview Abstract] 

R13.00003: Modulation of interphase, crossscale momentum transfer by preferentiallyconcentrated inertial particles Miralireza Nabavi Bavil, Mario Di Renzo, Jeonglae Kim Decaying homogeneous isotropic turbulence suspended with inertial point particles is investigated for understanding interphase, crossscale interactions. Using a wavelet multiresolution analysis, the crossscale transfer of turbulence kinetic energy (TKE) is quantified with a good spectral and spatial resolution and characterized as a function of the particle Stokes number $\text{St}_k$. Due to the spatiallylocal nature of the preferential concentration, the work done by the critical particles ($\text{St}_k = 1$) is increasingly intermittent in space. However, the subfilterscale energy transfer by the triadic interactions becomes less intermittent than that of the particlefree simulation. Conditioned analysis is performed by evaluating joint probability density function of wavelet statistics. In contrast to the preferential concentration in the oneway coupled simulations, smallscale kinetic energy is positively correlated with the coarsegrained particlenumber density where local TKE fluctuations are higher than the average. A collective work done by the highconcentration critical particles amplifies turbulent fluctuations, consistent to the unconditioned wavelet analysis. [Preview Abstract] 

R13.00004: Snow settling dynamics in atmospheric turbulence Jiaqi Li, Aliza Abraham, Michael Heisel, Filippo Coletti, Michele Guala, Jiarong Hong The study investigates the influence of atmospheric turbulence on the settling of snowflakes through in situ imaging of snowflakes in a field of view on the order of 10 m. Previous research based on such field measurements has shown that snowflakes exhibit typical features of inertial particles in turbulence: exponential tails of acceleration probability distribution function as compared to a Gaussian distribution, occurrence of clustering and enhanced settling velocity. However, those measurements relied on either particle tracking velocimetry (PTV) or particle imaging velocimetry (PIV) with limited analysis on the interaction between turbulent flow field and the snowflakes. In the current study, we present simultaneous measurements of atmospheric turbulence from a 20 m (width) x 40 m (height) PIV field and snowflake trajectories from a 3 m x 5 m PTV field of view within the PIV domain. Our analysis demonstrates clearly the interconnection among prominent vortical structures, snowflake clustering, and settling velocity enhancement in turbulence. [Preview Abstract] 

R13.00005: Applicability of LES models in capturing turbulence disruption for inertial particle laden turbulent flows Naveen Rohilla, Partha S Goswami, Pradeep Muramulla Predictingturbulence modulation through DNS at high Reynolds number particle laden turbulent flowsand for a system size of practical interest is almost impossible even with the recent development of high speed computing systems. Therefore, the objective of the present work is to explore the applicability and accuracy of LESin predicting turbulence attenuation. Using DNS, we have recently reportedthat the turbulence intensity decreases with increase in particle loading and at a critical volume loading there is a sudden collapse in turbulence. This happens due to reduction in the turbulent energy production rate [Muramulla et. al., JFM, 2020]. In the present work, we have explored the capability of different LES models to predict the critical volume loading for turbulence collapse at two different Reynolds numbers. It is observed that Smagorinksy and dynamic Smagorinsky models underpredict the critical volume loading at both the Reynolds numbers. However, ADM as a fluid SGS model correctly predicts the critical loading at low Reynolds number. But at high Reynolds number, turbulence collapse is not captured well using ADM model. In all the cases, we found that LES models fail to predict the accurate critical loading due to their inability to capture accurate turbulent production near critical volume fraction. [Preview Abstract] 

R13.00006: Liquid droplet formation and dispersion characteristics in a turbulent round jet. Peter Dearborn Huck, Rodrigo OsunaOrozco, Nathanael Machicoane, Alberto Aliseda We present experimental results for mixing characteristics in a twophase spray in a turbulent round jet spray for momentum ratios $M=(\rho_g/\rho_l)(v_g/v_l)^2=25176$, where $\rho_g$ ($\rho_l$) and $v_g$ ($v_l$) are the densities and velocities of the gas (liquid) phase, respectively. Spray formation near the nozzle creates droplets with a distribution of inertia that makes them interact differently with the gas turbulence. At low $M$ values, the spray is populated by droplets whose timescales are of the same order as the largest eddies. As $M$ increases, the droplets in the spray have low Stokes numbers with respect to these eddies. The resulting dropletturbulence interactions lead to mixing that results in concentration profiles that are broader than for a passive scaler and become progressively narrower as $M$ increases. We find a critical value ($M_c$) that separates these two regimes which controls the distribution of large and small particles across the spray. For $M 

R13.00007: Experimental Investigation of Twophase Flow in a Porous Plate Turbulent Wake Kristin Travis, Sarah E. Smith, Mickaël Bourgoin, Henda Djeridi, Raúl Bayoán Cal, Martín Obligado This study presents the findings of a wind tunnel experiment investigating the behavior of micrometric inertial particles in the turbulent wake of a stationary porous plate. Various concentrations [$\phi_v\in(4.3 \times 10^{6}  7.1 \times 10^{6})]$ of polydisperse water droplets (mean diameter of 40 $\mu$m) are compared to subinertial tracer particles. Hotwire anemometry, phase Doppler interferometry and particle image velocimetry were implemented in the near and far wake regions to study the complex dynamics of such particles. Turbulence statistics and particle size distributions are presented. Quadrant and Voronoi analysis are used to explore the shear effects of the particle wake interaction and preferential concentrations respectively. [Preview Abstract] 

R13.00008: A correction scheme for twoway coupled EulerLagrange approach on arbitrary grids Pedram Pakseresht, Sourabh V. Apte The accuracy of EulerLagrange pointparticle approaches can decay when the two phases are twoway coupled owing to the disturbance created by the pointparticle force on the background fluid flow. Such disturbance produces an error since the fluid force closure models often rely on the slip velocity computed based on the undisturbed fluid velocity, which is not readily available in the twoway coupled simulations. Recently, few schemes have been developed for correcting this issue, however, they lack generality and are all calibrated for specific computational grids or a limited range of flow parameters. In this work, a novel correction scheme is developed that is free of any empirical expression and applicable for (i) any arbitrary shaped structured or unstructured grid, (ii) a wide range of particle Reynolds numbers, (iii) any arbitrary particletogrid size ratio, and (iv) unbounded and wallbounded flows with complex geometries. The newly developed model is easy to implement, affordable, and highly accurate. Test cases performed on settling velocity of a single particle on different structured and unstructured grids, various particle Reynolds number, as well as unbounded and wallbounded regimes, show the capability of the present model for a wide range of applications. [Preview Abstract] 

R13.00009: Accurate modeling of group settling of a dense cluster of particles using the correctedpointparticle (cPP) approach Lokesh Jothi Vincent, Pedram Pakseresht, Sourabh V. Apte Modeling dense clusters of slightlyheavierthanfluid particles using a twoway coupled EulerLagrange approach requires accurate estimation of the fluid forces acting on the particles. Typical force closures require the undisturbed fluid velocity at the particles' location, which is not readily available in the twoway coupled simulations. In this work, a correction scheme developed by Pakseresht et al (JCP, 2020) is employed to recover the undisturbed fluid velocity from the available disturbed field. Fluid forces including drag, lift, added mass, and pressure gradient are employed to track particles. In addition, the history force, commonly neglected due to its expensive computation, is computed using a reducedorder model developed by Hinsberg et al (JCP, 2011). The present approach is tested for predicting the settling velocity of a single particle as well as a cloud of particles in a quiescent fluid. Different test cases are performed to cover a range of particle loading, various particle Reynolds numbers, different particle Stokes numbers, and different particletogrid size ratios. Results with and without the correction scheme are compared against available experimental data and the importance of the Basset history force is quantified for the studied cases. [Preview Abstract] 

R13.00010: Experimental measurements of particle transport modification in dense particleladen turbulent flows Roumaissa HASSAINI, Filippo Coletti Inertial particles at high volume fractions can modify the turbulence which in return affects the particle transport. For such flows the fluid and the particles behavior become challenging to measure and understand. We tackle this problem by studying experimentally particleturbulence interaction in a homogeneous turbulence chamber with negligible mean flow. Time resolved Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) measurements are carried out simultaneously to capture the fluid velocity and the particles position from the Kolmogorov to the integral scale. Two sets of parameters were used to vary the Stokes number by one order of magnitude while keeping the gravitational settling similar. The particle concentration was increased up to 5e5. We focus on the solid phase. A drastic change on the settling velocity has been observed due to preferential sweeping with a stronger modification for heavier clustered particles. Clustering has been reported to increase with the volume fraction associated with a different cluster size evolution for the different Stokes numbers. Independently of inertia an increase of the dissipation rate due to the drag effect can be linked to the enhancement of the turbulent kinetic energy. [Preview Abstract] 

R13.00011: On Turbulence and Particle Transport in Closed Rooms. Som Dutta, Shyuan Cheng, Aditya Parikh, Tadd Truscott, Paul Fischer, Leonardo Chamorro The Covid19 pandemic has brought the focus on the airborne transmission pathways of respiratory viruses and pathogens. It has been found to be substantially higher in indoor environments. However, the effect of turbulence generated by flow through HVAC systems on the transport of virusladen aerosols is not well understood. Studies of roomscale transport have primarily used RANS based turbulence closures coupled with Lagrangian particle tracking based model to simulate the transport of the aerosols. Here, we conduct highresolution Large Eddy Simulations (LES) of the flow and temperature in a closed room, with an inlet (located near the ceiling) and outlet located at diametrically opposite corners of the room. The flow is coupled with a Lagrangian particle tracking based model for transport of polydisperse aerosols of the diameter range known to be generated during talking, singing, and breathing (0.5  20 microns). We will briefly discuss the effect of airflow rate, point of injection, and aerosol size, on residencetime, deposition pattern, and accumulation hotspots of the virusladen aerosols. We also discuss the early and developed stages of the turbulence within the room, with emphasis on mixing, transport, and largescale motions as a function of time and asymptotic behavior. [Preview Abstract] 
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