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 zero-inertia particle coagulation in inertial-range turbulence [1]. Namely, starting from a monodispersion, the i-mer population increases as a power of time, where the i-dependent exponent involves the third-order scalar structure-function exponent due to the connection between particle number density and an inertial-range passive-scalar field. In effect, scalar intermittency boosts the likelihood that a pairwise coalescence event is promptly followed by another due to 3-particle (hence third-order) 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 measure-preserving 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 inertial-range 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, 1858-1881 (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 Zurita-Gotor, 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, 4873-4889] we have found that the drop arrays behave like strongly overdamped bead-spring chains, with springs representing effective inter-drop hydrodynamic interactions. As a result, the relaxation of perturbed chains is diffusive. This behavior is in contrast to the drop-chain dynamics in a confined Poiseuille flow, which is described by the first-order wave equation. To elucidate this difference, we analyze how elementary contributions of inter-particle interactions, i.e., (i) dipolar, (ii) quadrupolar, and (iii) swapping-trajectory effects influence the collective drop dynamics. Due to antisymmetry with respect to the flow reflection, the Hele--Shaw dipoles contribute to wave propagation in a particle array. The symmetric Hele--Shaw 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 fully-developed turbulence. In this study, we use the piston-cylinder 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 high-speed 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 bubble-eddy collision that has been widely used in describing bubble deformation and breakup in fully-developed 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 phase-field 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 Navier-Stokes 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 half-height), 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] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L28.00005: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 2:50PM - 3:03PM |
L28.00006: Measurements of Deformations of Fibers and Multi-armed 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 multi-armed 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 fiber-like 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 rubber-like polymer. We show that multi-armed 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 high-speed cameras to achieve high precision in measuring particle orientations and arm deformations with an uncertainty of roughly $10^{-4}$ rad. Multi-arm 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 Taylor-Couette 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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