Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session Z26: Suspensions: General |
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Chair: Lina Baroudi, Manhattan College Room: 234 |
Tuesday, November 22, 2022 12:50PM - 1:03PM |
Z26.00001: Flow instabilities and transition to turbulence in particulate Taylor-Couette flow Lina Baroudi, Joseph Olsen, Stephen Peluso In this study, we present an experimental investigation into the influence of suspended particles on flow instabilities and transition to turbulence in Taylor-Couette (TC) flow with a rotating inner cylinder and stationary outer cylinder. The apparatus has a radius ratio of \eta=r_i/r_o=0.882, where r_i and r_o are the radii of the inner and outer cylinders, and an aspect ratio of \Gamma=L/\delta=37.9, where L is the height of the inner cylinder, and \delta=r_o-r_i is the annular gap size. The suspensions are formed of non-Brownian particles of equal density to the suspending Newtonian fluid, and the ratio of the annular gap to the mean particle diameter (d_p) is \alpha=\delta/d_p= 20.5. The Reynolds number is varied over a large range (30\le Re \le4000), covering laminar and turbulent flow transitions for several particle volume fractions (0\le \phi \le0.30). For \alpha=20.5, we show that particles play a fundamental role in the observed instabilities and decrease the threshold at which turbulence can be sustained. |
Tuesday, November 22, 2022 1:03PM - 1:16PM |
Z26.00002: Lagrangian Measurements of Dense Suspensions in Turbulent Vortical Flows Adnan El Makdah, Moira Barnes, David E Rival Several studies have investigated the behaviour of dense suspensions in laminar and creeping flows. However, the physics of turbulent (high Reynolds) dense-suspension flows is still poorly understood. Traditionally, Eulerian measurement techniques, such as Particle Image Velocimetry, have been used to examine dense-suspensions flows. Although such Eulerian measurements provided great insights into flow physics, they cannot provide particle trajectories, which are essential in studying particle residence time and particle-wall interactions. In the current work, Lagrangian particle tracking techniques are used to examine dense suspensions of volume fractions up to 40% in a flow loop. Additionally, a shear-thinning analog fluid with a single phase is also examined, in which the results are compared with pure water and dense suspensions. Furthermore, different geometries are installed inside the pipe to create high-Reynolds turbulent vortical flows. A pathline extension method will examine particle residence time and particle-wall interaction. |
Tuesday, November 22, 2022 1:16PM - 1:29PM |
Z26.00003: Instabilities in two-dimensional suspension flows Rui Luo, Maxwell Marshall, Li Wang, Sungyon Lee We study the emergence of miscible fingering in quasi-two-dimensional suspension flows, by combining experiments and theory. We experimentally inject silicone oil into the mixture of the same oil and non-colloidal particles inside a highly confined channel. The gap thickness is comparable to the particle diameter, so that suspended particles form a monolayer inside the cell. Our experiments reveal that miscible fingering is observed at all concentrations, distinct from the continuum limit. In addition, the emergent fingers exhibit concentration-dependent wavelengths as well as continuous particle fluctuations, reminiscent of 2D droplet ensembles. To rationalize our observations, we develop a kinetic theory that implements long-range hydrodynamic interactions between highly confined particles. The theory qualitatively predicts the experimental observations. |
Tuesday, November 22, 2022 1:29PM - 1:42PM |
Z26.00004: An anisotropic clustering instability in a sheared suspension of magnetic particles subject to a magnetic field. Viswanathan Kumaran A suspension of magnetic particles in a viscous fluid exhibits a transition between a flowing state in the absence of a magnetic field and a jammed state with sample-spanning particle aggregates when a magnetic field is applied. The initiation of dynamical arrest of an initially well-dispersed sheared suspension is examined by considering the effect of inter-particle hydrodynamic and magnetic interactions. There is a disturance due to the magnetic field around one |
Tuesday, November 22, 2022 1:42PM - 1:55PM |
Z26.00005: Dynamics of flexible filaments in oscillatory shear flows Francesco Bonacci, Brato Chakrabarti, David Saintillan, Olivia Du Roure, Anke Lindner Understanding the transport and conformational dynamics of flexible microfibers in time-dependent flows is of key importance for the characterization of complex biological phenomena and the control of polymer-based material properties during processing. Here, we combine experiments in microfluidic channels and computational modeling to study the dynamics of elastic, Brownian, actin filaments submitted to oscillatory forcing. Unlike time-invariant shear flows, in which the emergence of morphological transitions is essentially governed by a single parameter, the elastoviscous number, that compares viscous to elastic restoring forces, the addition of an independent timescale in the problem makes way for a variety of unexplored behaviors. We show that the dynamics now strongly depends on a new dimensionless number ρ, comparing the maximum shear rate to the oscillation period, and θ0, the filament orientation at the beginning of each period. Of particular interest is the possibility of suppression of buckling instabilities for combined values of ρ and θ0, even in very strong flows. We explain this remarkable behavior through a weakly nonlinear Landau theory of buckling, in which we treat the filaments as inextensible elastic rods whose hydrodynamics are described by local slender-body theory. |
Tuesday, November 22, 2022 1:55PM - 2:08PM |
Z26.00006: Crack patterns in drying suspensions of binary fluid mixture Xiaolei Ma, Amir Pahlavan The drying of particle-laden binary fluid mixtures is a crucial process in diverse industrial settings such as ink-jet printing and coating. Here we report on the mechanical instabilities in drying suspensions of colloidal particles dispersed in binary fluid mixtures confined in a microfluidic channel. Our observations suggest that the mechanical instabilities of the drying particulate film can be manipulated by the hydrodynamic instabilities of the drying fluid mixtures. |
Tuesday, November 22, 2022 2:08PM - 2:21PM |
Z26.00007: Under Pressure: Fracture and Relaxation in Bulk Cornstarch Suspensions Paul Lilin, Jean E Elkhoury, Ivo R Peters, Irmgard Bischofberger We probe the fracture and relaxation characteristics of dense cornstarch suspensions, a complex fluid that exhibits discontinuous shear-thickening behavior. We inject air at a constant pressure into suspensions of different mass fractions of cornstarch in water placed in an open three-dimensional container. Because the suspension is opaque, fast X-ray radiography is required to image the growth of the air cavity upon air injection. The X-ray images reveal shapes ranging from smooth bubbles to sharp cracks. By measuring the air thickness, we find that both bubbles and cracks grow at a constant volumetric flow rate that increases linearly with the applied pressure, a remarkably simple behavior for a complex fluid. Surprisingly, the flow rate is not affected by an increase in the cornstarch mass fraction from 58% to 60%, despite major changes in the rheology of the suspension. Conversely, the air cavity shape and relaxation dynamics strongly depend on the mass fraction: sharp cracks relax into bubbles with a relaxation time scale that depends on the mass fraction. This relaxation process under constant stress will yield new insights into the transition of the material from the discontinuous shear-thickening state to the fluid state. |
Tuesday, November 22, 2022 2:21PM - 2:34PM Author not Attending |
Z26.00008: Pre-shear holds the key in understanding discontinuous shear thickening in dense suspensions Tabish Khan, Prabhu R Nott The phenomenon of discontinuous shear thickening (DST) in dense non-Brownian suspensions, |
Tuesday, November 22, 2022 2:34PM - 2:47PM Not Participating |
Z26.00009: Mesoscopic simulations of shear-induced phase transition in active colloidal suspensions Ayten G Bayram, Fabian Jan Schwarzendahl, Hartmut Löwen, Luca Biancofiore Phase transition and collective dynamics of dense active colloidal suspensions is a fascinating topic in soft matter physics, in particular for out-of-equilibrium systems. These systems are challenging to describe with conventional methods due to the coexistence of different length-time scales and the lack of molecular-level details. The issue is to include all together the effects of thermal fluctuations, hydrodynamic interactions and spatio-temporally varying forces. |
Tuesday, November 22, 2022 2:47PM - 3:00PM |
Z26.00010: Suspension plug in oscillatory pipe flow Zilong He, Sungyon Lee Non-colloidal particles under shear are known to exhibit irreversible, cross-stream migrations at even low Reynolds numbers. We experimentally investigate this phenomenon in a suspension plug of finite lengths inside a cylindrical tube, subjected to an oscillating pressure-driven flow. The plug consists of neutrally buoyant, non-colloidal particles in the viscous fluid. By applying the refractive index matching techniques, we visualize the particle dynamics on a center plane of the tube and track the trajectories of individual particles under applied strain. Our preliminary results demonstrate the extension of the suspension plug in both streamwise and spanwise directions after multiple oscillations, which are directly tied to the irreversible migration of particles across streamlines. In this talk, we discuss our new experimental findings and discuss the physical mechanism based on a simplified model. |
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