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 R11: ParticleLaden Flows: General (5:00pm  5:45pm CST)Interactive On Demand

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R11.00001: Dynamics of spheres falling in quiescent flows Facundo Cabrera, Mickael Bourgoin, Nicolas Plihon Despite the apparent simplicity of a single sphere falling in a quiescent flow, far enough from Stokes conditions, a rich dynamics has been found. Simulations have shown the existence of several particle trajectory regimes in a quiescent flow, whose onsets are determined by particlefluid density ratio ($\rho_s/\rho_f$) and Galileo number. These regimes are mainly characterised by the presence or absence of oscillations and the trajectory angle with respect to the gravity.\\ Here, experiments to test the validity of the aforementioned simulations are presented. In particular, the dynamics of heavy spheres with particlefluid density ratios between $(1.1, 10)$ and Galileo numbers between $(150, 400)$ has been studied. We have performed an exploration of the different trajectory regimes modifying the Galileo number by changing the viscosity and using particles with several densities. While the trajectories are measured using a 3D PTV system. [Preview Abstract] 

R11.00002: Toward a Mean Velocity Scaling in Variable Property ParticleLaden Channel Flow Jacob West, Sanjiva Lele In a particlebased solar receiver, dense particles in a turbulent duct flow are radiatively heated, in turn heating the surrounding air. When the particle loading and radiation intensity are large enough, there is significant gas expansion, which sets up an accelerating particleladen flow with substantial density and viscosity variation. Using a suite of heated, particleladen channel flow simulations, we characterize the turbulent mass, momentum, and energy transport associated with both the particle and fluid phases, as well as the fluctuating particle number density and transmitted radiation fields. In this complex flow, we find that the VanDriest transformation is not able to collapse the mean velocity profiles, so we examine alternate scalings. The suite of channel flow simulations were conducted at $Re_{\tau}\approx235$, using Lagrangian point particles with moderate Stokes number ($St^+\approx7.5$) and particle mass loadings ranging from $10\%200\%$. Radiation intensities were chosen so that the ratio of radiative heat flux to the sensible heat of the mixture range from $0.4  5.8$. [Preview Abstract] 

R11.00003: Particle capture by drops in Turbulence Arash Hajisharifi, Cristian Marchioli, Alfredo Soldati We examine the capture of subKolmogorov inertial particles by deformable liquid droplets in dilute turbulent channel flow. To simulate this solidliquidliquid system, we exploit a EulerianLagrangian methodology based on DNS of the Continuity, NavierStokes and CahnHilliard equations and on the solution of the Lagrangian equation of particle motion. The carrier flow and the droplets have same density and viscosity. To model the particleinterface interaction, we consider a capillary force based on the liquidliquid surface tension and the distance from the particle center to the nearest point on the fluid interface: This force is exerted only in close proximity of the (diffuse) interface and drives particle capture. Simulations with and without interparticle collisions were performed to examine particle capture and subsequent accumulation at the interface, which are found to depend on the combined action of turbulence and particle inertia. Capture and trapping is higher for lower inertia particles, and accumulation is found to occur in the highpositivecurvature regions of the interface. This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie SklodowskaCurie grant agreement No 813948. [Preview Abstract] 

R11.00004: Inertial particle dynamics with history effects at fixed computational cost Divya Jaganathan, S Ganga Prasath, Vishal Vasan, Rama Govindarajan The unsteady dynamics of a small, spherical particle in a nonuniform flow is described by the MaxeyRiley (MR) equation. The BassetBoussinesq term in the equation, which is an integral of the particle’s history weighted by timedependent kernel, is known to impact transient dynamics but is often neglected or approximated due to its computational cost which grows linearly with the time of simulation. We address this by using an evolution equation for the history term due to Prasath et al.(2019). They showed that the MR equation with BassetBoussinesq term can be posed as a Robin boundary condition to the 1D heat equation. This formulation and the closedform expressions it affords, leads to a new timeiterative scheme to evaluate the full MR equation without approximation for generic nonlinear fluid flows. This method has a fixed computational cost per timestep and gives spectral accuracy, thus making it amenable to longduration and multiparticle runs. We further reduce the cost associated with the iterative solver by employing only local velocity gradient information to compute the history effect. We present our numerical scheme to handle the evolution of a particle with history effects in 2D nonlinear flows. [Preview Abstract] 

R11.00005: Effect of Center of MassOffset on Settling and Rising Spheres Jelle Will, Dominik Krug We experimentally investigate the effect an offset center of mass has on rising and settling spheres in a still fluid. We find that the dynamics and kinematics of the particles are extremely sensitive to offsets as small as 1$\%$ of the particle radius. We uncover that the governing parameter for the particle behaviour is the particle Froude number, which is defined as the ratio between a rotational timescale of the particle and the characteristic time of the vortex shedding. It is found that the frequency and the amplitude of particle oscillations, as well as the particle drag coefficient vary strongly as a function of $Fr$. These effects are strongest for $0.08 \le Fr \le 0.14$, where resonance occurs between the rotational and vortex shedding frequencies. Furthermore, our results indicate that the particle drag does not correlate well with the amplitude of path oscillations but more sensitively depends on the amount of particle rotation. In rising particles, such rotations are enhanced by the Magnus lift force resulting in an increase in drag. Contrary to this, for settling particles the Magnus lift force counteracts the particle rotation, such that no drag increase is observed in this case. [Preview Abstract] 

R11.00006: Targeted particle delivery via reconnecting vortex rings Joshua Wawryk, Joseph Mouallem, Hamid Daryan, Zhao Pan, JeanPierre Hickey We propose and characterise a method for targeted delivery of finitesized particles within a streamwise evolving channel flow. By randomly seeding particles at specific Stokes numbers within the core of vortex rings, the solidphase is transported in the streamwise direction of the channel flow via selfadvection of the vortex ring. The streamwise particle advection can then be halted and transferred into the wallnormal direction through antiparallel vortex reconnection. To this end, a pair of nearly coaligned vortex rings are setup to reconnect at a streamwise distance, thus enabling a transfer of the solid particles to the side walls of the channel. This talk will propose a systematic approach towards targeted particle delivery and quantify the mass transport, through highfidelity direct numerical simulations, to the side walls of a laminar channel flow. This approach can be extended for use in drug delivery, surface treatment of internal flow passages, and food processing industry. [Preview Abstract] 

R11.00007: Maximum drag reduction asymptote for particulate pipe flows Nishchal Agrawal, George Choueiri, Bjorn Hof Adding polymers or particles to a flow can alter the drag experienced by it. For instance, polymers in a flow reduce drag but their ability is bounded by a limit, the maximum drag reduction asymptote. However, the effect of particles on drag is ambiguous, with studies reporting contradicting observations; even in cases where particles are reported to reduce drag no asymptotic limit is know. The ambiguity arises because in addition to particle concentration, particle shape, size and density affect the drag. Hence, various particles behave differently in distant ranges of Re and concentration. In the present study, we experimented in a pipe flow setup with neutrally buoyant spherical and elongated particles, covering wide ranges of both Re and concentration. Based on friction factor, we found that spherical particles do not show drag reduction at any Re while the elongated particles do within an specific interval of Re. This interval strongly depends on particle concentration and relative size of pipe to particle, and within this interval the friction factor reaches a minimum value. These drag reduction maxima fall onto a distinct curve which can be considered the maximum drag reduction asymptote for a given particle shape, irrespective of the pipe diameter or concentration. [Preview Abstract] 

R11.00008: Methods for improving the particle sizing resolution of inertial impactors using ring shaped deposits Shivuday Kala, J.R. Saylor Inertial impactors are devices used to measure the size distribution of particles in a flow. These instruments are robust and widely used, however the number of bins in the resulting size distributions are limited by the number of impactors in an impactor cascade. Recent research shows that under proper conditions, the normally disc shaped deposition pattern takes the form of a ring whose diameter can be correlated to the particle diameter. This result opens the door to much higher resolution particle size distributions for an impactor cascade, or even for a single impactor. Herein, experiments are presented revealing these ringshaped deposition patterns on glass substrates for a range of particle sizes, further illustrating the effect. The ring diameter is correlated to the particle diameter and Stokes number. Additionally, computer simulations of particle trajectories are presented, revealing the underlying mechanism of this effect. [Preview Abstract] 

R11.00009: Dilute suspensions over and through porous structures; the impact of permeability and porous thickness Eileen Haffner, Theresa Wilkie, Parisa Mirbod Suspension flows at various concentrations have been studied significantly within impermeable/smooth channels. Likewise, porous media has been studied in various engineering applications including carbon nanotube forests applications. However, there are few studies in terms of the coupling between these two flows. This study examines a pressuredriven, dilute suspension flow in a channel where the bottom wall replaced by porous media. The properties of the porous media were manipulated to see how they change the velocity profiles and parameters at the suspensionporous interface. A dilute, nonBrownian, neutrallybuoyant suspension of rigid spherical particles with 3{\%} bulk volume fraction was passing over rigid porous media consisting of cylindrical rods perpendicular to the flow direction. It was observed that as the permeability of porous media increases the location of the maximum velocity within the freeflow region shifts towards the interface. Properties at the interface such as, the dimensionless slip parameter, slip length, slip coefficient, and penetration depth are all greatly affected by the porous media thickness and permeability. [Preview Abstract] 

R11.00010: Novel Indirect Particle Temperature Measurement Methodology Using IR and Visiblelight Cameras Jesus Ortega, Guillermo Anaya, Clifford Ho, Peter Vorobieff, Gowtham Mohan The particle temperature measurements in a gravitydriven flows present a unique challenge due to its transient nature and flow's stochastic. While attempts to estimate the bulk particle temperature have been conducted using contact and noncontact methods, a definitive and practical solution is yet to be found. This work focuses on a novel noncontact method using a highspeed IR camera and a visiblelight camera (Nikon D3500) to accomplish this indirect particle temperature measurement. The thermograms and image sets collected by the cameras allow for the measurement of the apparent particle temperature and the opacity of a particle plume. An inhouse postprocessing code based on Planck's theory allows to calculate the true particle temperature from the apparent temperature obtained from the thermograms. The particle temperature data are compared with the empirical model of the bulk particle temperature yielding agreement with 95{\%} confidence (2$\sigma )$. [Preview Abstract] 

R11.00011: Electron Temperature Measurement using Collisional Radiative Model in PFRCII Christopher Jakuback Replace this text with your abstract body. [Preview Abstract] 
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