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 G36: Suspensions: FluidParticle Interaction 
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Chair: Brian Utter, Bucknell University Room: Georgia World Congress Center B408 
Monday, November 19, 2018 10:35AM  10:48AM 
G36.00001: Indirect Probing of the StrainRotation Balance in NonNewtonian Turbulence with Inertial Particles Michael Sinhuber, Joseph G Ballouz, Nicholas Ouellette It is commonly thought that small amounts of polymer additives alter the strainrotation balance in turbulent flows. However, as for experimental evaluation of this hypothesis one needs to resolve the velocity gradients in turbulent flows, quantitative evidence for this statement is mostly lacking. Velocity gradients are notoriusly challenging to measure in most experiments, so here we take an alternate, indirect approach to answer the question on how polymers affect turbulent flows. By using the wellknown preferential concentration effect of inertial particles and the energy flux balance model for polymer turbulence, we can probe concentration effects on the strainrotation balance. We do so by using a classical vonKàrmàn water flow with highmolecularweight polymer additives of varying concentration and weakly inertial particles. We compute the pair correlation function and show that particle clustering and hence the strainrotation balance is monotonically altered with increasing polymer concentration. 
Monday, November 19, 2018 10:48AM  11:01AM 
G36.00002: A novel immersed boundarylattice Boltzmann method for fluidstructure interactions involving viscoelastic fluids Jingtao Ma, Fangbao Tian, Joseph C.S. Lai, John Young This work presents a novel immersed boundarylattice Boltzmann method for fluidstructure interactions involving viscoelastic fluids. This method has been validated by conducting a few typical viscoelastic flows: 2D liddriven cavity, a 2D rigid particle migration in Couette flow, a 3D rigid particle rotation in shear flow and a 3D rigid particle sedimentation. The present results show good agreement with previous results from different sources. The present method has been also applied to several problems involving fluidstructure interactions: a 2D elastic capsule deformation in the viscoelastic fluid shear flow, a 3D elastic capsule deformation in the viscoelastic fluid shear flow, and a 3D flexible plate motion in the viscoelastic fluid uniform flow. The results suggest that the viscoelasticity of the fluids has great effects on the behaviours of the elastic capsules and flexible plate. 
Monday, November 19, 2018 11:01AM  11:14AM 
G36.00003: Robustness of selfaligning particles in simple shear flow towards rotation due to Brownian motion and hydrodynamic interactions Neeraj N. Sinai Borker, Abraham D. Stroock, Donald L. Koch We show that a slender, rigid selfaligningring that attains an equilibrium orientation in a simple shear flow (SSF) can resist rotation against rotary Brownian motion as well as pairwise interactions with other particles under certain conditions. A selfaligning particle reaches an equilibrium orientation such that its slender dimension(s) makes an angle β_{S}≪1 with the velocity gradient direction of the SSF of shear rate γ. The particle wobbles around the equilibrium orientation if Pe =γ/D_{r}≫β_{S}^{3}, where D_{r} is the rotational diffusivity of the particle. Using rotary Brownian Dynamics, we demonstrate that the particle tumbles if Pe≪β_{s}^{3} with a frequency smaller than that of an equivalent rotating particle of the same aspect ratio. Using slender body theory, we show that a selfaligning ring also wobbles around its equilibrium orientation due to pairwise interactions with other rings. Therefore, individual particles in a dilute suspension of selfaligning rings remain aligned near the flow vorticity plane for Pe≫β_{S}^{3} and thus the suspension has a smaller intrinsic viscosity compared to a suspension of tori of the same aspect ratio. Our result opens a new avenue to tune the rheology of particle suspensions by changing the shape of individual particles. 
Monday, November 19, 2018 11:14AM  11:27AM 
G36.00004: Nearwall dynamics of a neutrallybuoyant particle in Hiemenz flow Qing Li, Micheline Abbas, Jeffrey Morris, Eric Climent, Jacques Magnaudet We perform a DNS based on an Immersed Boundary Method to study neutrally buoyant spherical particle motion on the axis of an axisymmetric stagnation point flow at a wall (Hiemenz flow). We seek to find conditions leading to solid collision with the wall. Depending on the ratio between particle inertia and viscous boundary layer thickness, the force exerted on the particle exhibits two distinct behaviors. Far from the wall, the slip Reynolds number is vanishingly small, implying that the particle behaves essentially as a tracer, but its finite size implies an ambient inertial force nearly identical to the force that would decelerate the equivalent volume of fluid. Near the wall, the slip Reynolds number increases as the particle approaches the wall, and several forces besides the ambient inertial force play a role. We investigate the stress profile on the particle surface to identify the origin of these forces : ambient force due to finite size and nonuniform flow, lubrication due to squeeze film, and addedmass due to acceleration of particle and fluid. Using the DNS results, we build a model which may be used with underresolved simulation and show that its results agree satisfactorily with wellresolved simulation. 
Monday, November 19, 2018 11:27AM  11:40AM 
G36.00005: Graphene nanoplatelets attain a stable orientation in a shear flow Catherine Kamal, Simon Gravelle, Lorenzo Botto Our group is interested in the hydrodynamics of graphene. The study of a rigid graphene nanoplatelet in a simple shear flow offers the opportunity to revisit basic assumptions regarding the rotational motion of platelike particles. Current theories assume a nanoplatelet suspended in a simple shear flow should rotate continuously following a Jeffery's orbit. We show by combining Molecular Dynamics for a graphenewater system, Boundary Integral simulations, and theory, that a rigid nanoplatelet with normal in the plane of the shear flow does not follow Jeffery's orbit, but rather aligns itself at a small inclination angle with respect to the flow direction. This unexpected result is due to the slip velocity at the graphenewater surface and to molecular edge effects. 
Monday, November 19, 2018 11:40AM  11:53AM 
G36.00006: Sedimentation of elastic loops in a viscous fluid Piotr Szymczak, Magdalena GruzielSlomka, Pawel Kondratiuk, Maria EkielJeżewska We explore numerically the dynamics of elastic loops sedimenting in a viscous fluid. We show that an interplay between elastic and hydrodynamic forces in such a system can give rise to surprisingly rich variety of periodic orbits and stationary shapes. The two main parameters controlling the motion turn out to be the bending stiffness of the chain and its length. Stiff loops tend to keep the circular shape and settle vertically (with the axis of the ring perpendicular 
Monday, November 19, 2018 11:53AM  12:06PM 
G36.00007: Minimizing particle induced fluid motion in a vertically rotating system Md Mahmudur Rahman, John Ellery Payne, Stuart Joseph Williams Liquid rotates as a rigid body in a confined system rotating vertically, though introducing particles in the solution generates fluid motion due to particle sedimentation. Based on rotational speed three different regimes (microfluidic mixing, particle suspension, and settling due to centrifugal acceleration) can be established for a certain particlesolution selection. The goal of our investigation is to demonstrate the existence of longterm particle suspension regime and, thus, characterize colloidal behavior. After a certain time, if other parameters remain constant, system reach its constant microfluidic motion state in a certain rotational speed at a negligible centrifugal acceleration. At that equilibrium motion state, we correlated particleinduced fluid motion per rotation with a proposed nondimensional number which is the ratio of inertia forces on fluid cell caused by particles to the viscous resistance. We quantified average fluid motion at different particle concentration and at different rotational speeds and compared it to the proposed nondimensional number. Further, particle distribution was observed at different rotational speeds to quantify the effect of centrifugal acceleration. 
Monday, November 19, 2018 12:06PM  12:19PM 
G36.00008: Particles sedimenting in a permeable medium Maria L. EkielJezewska, Marta Gruca, Marek Bukowicki In many systems found in nature or in technological contexts, microobjects (particles, microorganisms, etc.) sediment in a more or less crowded environment – in a fluid with solidlike intrusions, which increase the effective friction force exerted on them by the fluid. Therefore, it is interesting to investigate how this increased friction affects basic features of manybody dynamics, known for Stokes fluids: chaotic scattering, related to existence of periodic, usually unstable orbits, and formation of longlasting particle clusters. In this work, such a crowded environment is modeled as porous medium. We study sedimentation of manyparticle systems for decreasing values of the medium permeability. The fluid motion is described by the BrinkmanDebyeBueche equations, and the motion of particles by the corresponding pointforce model. We investigate dynamics of many particles which initially form 2 or 4 coaxial rings. For large permeability, we find a family of periodic orbits, analogical to those found in Stokes fluids; for smaller permeability, such solutions are absent and particles do not form longlasting clusters. Results might be useful for medical and industrial applications.

Monday, November 19, 2018 12:19PM  12:32PM 
G36.00009: Bubble and particle dynamics in a gassolid fluidizedbed Jubeom Lee, Hyungmin Park We experimentally investigate the dynamics of gas and solid phase (buoyancydriven particle mixing) in twodimensional fluidizedbed while varying the gas flux, which is measured by the combination of highspeed 2phase PIV and PTV. To ensure the stage of fluidization, the pressure drop across the bed is also measured together. For the particle we use spherical glass bead (Geldart Btype, size: 500 μm, density: 2500 kg/m^{3}), and the gas flux is varied from 3 to 9 m^{3}/h. In the considered range, the fluidization regime covers from minimum to fastfluidization regimes with increasing the gas flux. It is found that solidparticles are globally carried upward at the core region but fall near the sidewalls, depending on the gas flux. On the other hand, the rising bubbles in the bed locally interfere with the particles, resulting in nonuniform fluidization (agglomeration, particle deceleration), which is exacerbated with increasing the gas flux. The statistical analysis on the bubble size in the bed shows that the equilibrium between bubble coalescence and breakup determines the maximum stable bubble size. The effect of different particle size on the bubble dynamics will be discussed additionally. 
Monday, November 19, 2018 12:32PM  12:45PM 
G36.00010: Abstract Withdrawn 
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