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 L28: Particle Laden Flows: Deformable Particles 
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Chair: Alfredo Soldati, TU Wien Room: 610 
Monday, November 25, 2019 1:45PM  1:58PM 
L28.00001: A minimal stochastic model capturing intermittency effects on coagulation in turbulence Alan Kerstein, Steven Krueger A recent theory, confirmed by direct numerical simulation, established that intermittency dominates the early transient period of zeroinertia particle coagulation in inertialrange turbulence [1]. Namely, starting from a monodispersion, the imer population increases as a power of time, where the idependent exponent involves the thirdorder scalar structurefunction exponent due to the connection between particle number density and an inertialrange passivescalar field. In effect, scalar intermittency boosts the likelihood that a pairwise coalescence event is promptly followed by another due to 3particle (hence thirdorder) correlations. The following minimal model reproduces the exponent values and related properties. The system state is a list of particle locations. The triplet map, a measurepreserving map often used in 1D simulations and newly extended to 3D by applying it to planar slabs instead of line intervals [2], displaces particles within a given slab along the (x, y, or z) coordinate normal to the slab faces. Sampling of map occurrence times and slab orientations, locations, and widths incorporates inertialrange phenomenology. [1] J. Bec et al., Phys. Rev. E 93, 031102(R) (2016). [2] S. K. Krueger, A. R. Kerstein, J. Adv. Model. Earth Sys. 10, 18581881 (2018). [Preview Abstract] 
Monday, November 25, 2019 1:58PM  2:11PM 
L28.00002: Dynamics of chains of deformable particles in strongly confined Poiseuille and Couette flows Sagnik Singha, Abhilash Reddy Malipeddi, Mauricio ZuritaGotor, Kausik Sarkar, Jerzy Blawzdziewicz In a strongly confined system of deformable drops shear flow triggers their rearrangement into highly ordered linear arrays oriented in the flow direction. In our recent investigation [Soft Matter, 2019,15, 48734889] we have found that the drop arrays behave like strongly overdamped beadspring chains, with springs representing effective interdrop hydrodynamic interactions. As a result, the relaxation of perturbed chains is diffusive. This behavior is in contrast to the dropchain dynamics in a confined Poiseuille flow, which is described by the firstorder wave equation. To elucidate this difference, we analyze how elementary contributions of interparticle interactions, i.e., (i) dipolar, (ii) quadrupolar, and (iii) swappingtrajectory effects influence the collective drop dynamics. Due to antisymmetry with respect to the flow reflection, the HeleShaw dipoles contribute to wave propagation in a particle array. The symmetric HeleShaw quadrupoles together with the swapping trajectory effect produce diffusive relaxation in Couette flow and either wave decay or growth in Poiseuille flow. [Preview Abstract] 
Monday, November 25, 2019 2:11PM  2:24PM 
L28.00003: Breakup of bubbles driven by vortex ring collision Yinghe Qi, Carl Urbanik, Noah Corbitt, Ashwanth Salibindla, Rui Ni We present an experimental investigation of bubble breakup at the moment when two vortex rings collide with each other head on at high Reynolds numbers. At this moment, as the vortex cores break into finer scales, bubbles will experience strong fluctuations of local shear and pressure at multiple length scales, reproducing a flow environment that bubbles tend to experience in fullydeveloped turbulence. In this study, we use the pistoncylinder arrangement to produce and control the vortex ring collision, and the timing of bubble injection is adjusted to vary the distance between bubbles and the location where two vortex cores touch each other. Four highspeed cameras are used to simultaneously measure both the bubble breakup process as well as the surrounding flow. This study will help us to explore the idea of bubbleeddy collision that has been widely used in describing bubble deformation and breakup in fullydeveloped turbulence. [Preview Abstract] 
Monday, November 25, 2019 2:24PM  2:37PM 
L28.00004: Dynamics of large and deformable bubbles in turbulence Labanca Gabriele, Giovanni Soligo, Alessio Roccon, Alfredo Soldati The dynamics of large, deformable bubbles in a turbulent channel flow is investigated coupling direct numerical simulations of turbulence with the phasefield method (PFM). In the framework of the PFM a marker function (phase field) defines the local concentration of each phase; the phase field is uniform in the bulk of the phases and undergoes a smooth transition across the interface. All fluid properties are defined as proportional to the phase field. An interfacial term (based on the Korteweg tensor) in the NavierStokes equation accounts for the effects of a deformable interface on the flow field. We will present the effects of density and viscosity contrasts between the dispersed and the carrier phase at a constant shear Reynolds number, $Re_\tau=300$ (ratio between inertial and viscous terms, defined on the channel halfheight), and at a constant Weber number, $We=1.5$ (ratio between inertial and surface tension forces). In particular, the effects of density and viscosity contrast between the two phase on the dispersed phase morphology (drop distribution, Sauter mean diameter, interfacial area) and the local flow field will be investigated and detailed. [Preview Abstract] 

L28.00005: ABSTRACT WITHDRAWN 
Monday, November 25, 2019 2:50PM  3:03PM 
L28.00006: Measurements of Deformations of Fibers and Multiarmed Particles in Fluid Flows Bardia Hejazi, Lee Walsh, Greg Voth We measure the deformation of fibers and particles made of 3 and 4 slender arms. The multiarmed particles are triads (3 symmetric arms in a plane) and tetrads (4 symmetric arms separated by the tetrahedral angle) with rigid arms connected near the center of the particle by a weak rubber joint. For fiberlike particles we used two arms joined at the center by a weak joint. The particles are 2cm in diameter and are 3D printed using a soft rubberlike polymer. We show that multiarmed particles deform at lower order of the aspect ratio of the arm in uniform velocity gradients compared to buckling and bending of fibers. We first examine triads in the turbulent flow of a vertical water tunnel and use 4 highspeed cameras to achieve high precision in measuring particle orientations and arm deformations with an uncertainty of roughly $10^{4}$ rad. Multiarm particles deform more readily than fibers, but the measured deformations in the water tunnel are still small and only slightly larger than our measurement uncertainty. We continue our study by measuring the deformation of fibers and tetrads in a TaylorCouette apparatus. In these experiments we have higher velocity gradients and use a more viscous fluid than water which allows us to measure larger deformations. [Preview Abstract] 
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