Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session N18: Fluids VIIIFocus
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Sponsoring Units: DFD Chair: Panklaj Rohilla, Georgia Institute of Technology Room: Room 210 |
Wednesday, March 8, 2023 11:30AM - 12:06PM |
N18.00001: Leroy Apker Award Winner: Adam Dionne Invited Speaker: Adam Dionne Active fluid transport is a hallmark of many biological transport networks. While animal circulatory systems generally rely on a heart to drive flows, other organisms employ decentralized local pumps to distribute fluids and nutrients. We study one such organism, the slime mold Physarum polycephalum. Based on a network model combining active elasticity and fluid transport, we identify a set of contractile modes specific to each network topology. Modes corresponding to large-scale oscillations are found to be preferentially and robustly excited in both model simulations and in experimental data obtained from living Physarum plasmodia. These dominant modes are computed explicitly and shown to drive large-scale flows within the organism. We go on to use these modes to decompose Physarum’s behavior when studying a specific behavior of the network, nutrient transport. We characterize the modal composition that optimizes for nutrient dispersal throughout the network by using transport simulations. These results provide a conceptual framework for understanding active decentralized transport in Physarum and other contractile biological networks such as the brain vasculature, and decentralized transportation networks more generally. |
Wednesday, March 8, 2023 12:06PM - 12:18PM |
N18.00002: Simulating liquid-gas interfaces and moving contact lines using the immersed boundary method Pejman Sanaei, Charles Puelz, Daniel Chin, Michael Y Li In this work, we combine the immersed boundary method with several techniques to simulate a moving liquid-gas interface on a solid surface. The first technique defines a moving contact line model and implements an extended Generalized Navier Boundary Condition at the immersed solid boundary. The static and dynamic contact line angles are endogenous instead of prescribed, and the solid boundary can be non-stationary with respect to time. The second technique simulates both a surface tension force and an unbalanced Young force with one general equation that does not involve estimating local curvature. The third technique splices liquid-gas interfaces to handle topological changes such as the coalescence and separation of liquid droplets or gas bubbles. Finally, the forth technique re-samples liquid-gas interface markers to ensure a near-uniform distribution without exerting artificial forces. We demonstrate empirical convergence of our methods on non-trivial examples and apply them to several benchmark cases, including a slipping droplet on a wall and a rising bubble. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N18.00003: Numerical investigation on the effect of the in-situ photopolymerization of coalescence behavior of non-Newtonian polymer drops Vishal Sankar Sivasankar, Sai A Etha, Siddhartha Das The post-deposition kinetics of the drops play a crucial role in the morphology and hence the quality of the printed structure created using any of the droplet-based printing processes such as inkjet printing, aerosol jet printing (AJP), electrohydrodynamic jet printing (EHD), etc. For 3D printing of photo-curable materials, such post-deposition kinetics include the interplay between impact, spreading, coalescence, and photo-induced curing of the deposited drops. In this study, we employ direct numerical simulations to probe the coalescence behavior, of two non-Newtonian, polymeric drops in the presence of photocuring UV radiation. Coalescence dynamics, which is quantified by the time evolution of the height (h) and width (W) of the growing bridge formed by coalescing drops, is investigated for different photo-curing conditions seen in the aerosol jet printing (AJP) process. Further, we compare this complex thermo- fluid-solutal behavior of the coalescing drops by tracking the evolution of the curing front inside the photocuring drops. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N18.00004: Fluid Droplets in Acoustic Force Fields Probed with the Immersed Boundary Method Jacqueline Sustiel Acoustic trapping relies on the forces and torques exerted by sound waves to localize granular materials and transport them along three-dimensional trajectories. The composite wave-matter system can display complex emergent dynamical behavior arising from forces mediated by scattered waves. This phenomenology becomes substantially richer when the particles themselves can be deformed by acoustic forces, as is the case for viscous fluid droplets in acoustic traps. We demonstrate how to model acoustic forces at the surface of acoustically levitated drops using the immersed boundary method (IBM), and how those forces drive complex shape deformations and near-field fluid flows which modify single- and multi-droplet dynamics. These simulations cast light on such outstanding anomalies as the tendency of steadily levitated droplets to spin and spinning droplets to form chains. |
Wednesday, March 8, 2023 12:42PM - 12:54PM |
N18.00005: Characterization of magnetically levitated water drops Giovanna Truong, Yiqi Wang, Juan Recoaro, Yogesh Patil, Jack G. E Harris In order to isolate, manipulate, and measure macroscopic objects with high precision, levitation has proven a promising avenue. Previously, we described a tabletop magneto-gravitational trap that used permanent magnets to stably levitate glass microspheres. Now, we present the characterization of the loading and center-of-mass motion of water droplets of tens of micrometers in diameter in the same trap. We compare the resonant frequencies of oscillation along the three principal axes of the trap with results based on numerical simulation of the trapping potential. We will also discuss surface modes of the levitated water drops and techniques for noninvasive measurement thereof. Since a longer-term goal of this work is to address some of the outstanding puzzles concerning supercooled water[1-3], we will describe progress towards realizing a similar trap inside an environmental chamber that can provide the necessary range of pressure and temperature. |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N18.00006: Droplet Adhesion Revisited: Experiments and Theory Yinfeng Xu, Muhammad S Sadullah, Himanshu Mishra, Sankara Narayana Moorthi Arunachalam, Peng Zhang Sessile and pendant droplets are commonplace in natural and applied contexts, such as dew or rain drops adorning plants and windowpanes. These drops can be removed by either sliding and overcoming lateral adhesion or via perpendicular detachment by overcoming normal liquid–solid adhesion. While the sliding motion has been studied extensively, the normal detachment motion has received less attention; in fact, the normal component is often related to the liquid–solid work of adhesion that is described by the Young–Dupre equation. In this contribution, we combine experiment and theory to pinpoint the normal force needed to detach a liquid droplet from a flat surface with intrinsic contact angle varying from 40°–100°. We employed the Centrifugal Adhesion Balance (CAB) to measure the detachment force of a liquid droplet. Analysis of droplet shapes at for a wide range of body forces revealed that the body force is balanced by the difference between the forces due to the surface tension and the Laplace pressure, i.e., the force due to the work of adhesion has no bearing on the normal droplet detachment. The experimental findings are in excellent agreement the predictions of the lattice-Boltzmann (LB) simulations and the numerical solution of a modified Young–Laplace equation. Specifically, as the body force reaches a critical value the droplet cannot maintain a stable shape and detaches; with the increasing intrinsic contact angle, the non-dimensional normal critical force decreases monotonically. These findings challenge the conventional wisdom on the normal droplet adhesion's dependence on the work of adhesion. |
Wednesday, March 8, 2023 1:06PM - 1:18PM |
N18.00007: On the Squeeze Film Levitation Phenomenon in Incompressible Liquid Environments Mostafa A Atalla, Ron van Ostayen, Aimée Sakes, Michaël Wiertlewski Transverse vibrations can levitate objects in air, via the squeeze-film effect. The underlying physics of this phenomenon is attributed to the non-linear compressibility of the viscous air film, well captured by the Reynolds lubrication theory. A similar levitation has been demonstrated in liquids, however, the working mechanism of the levitation in the incompressible liquid case is unclear, with the existing theories contradicting documented experimental evidence. In this study, we conduct a time-average analysis on the coupled dynamics of the levitated object and the liquid film. Our analysis reveals that in-liquid levitation is driven by inertial forces, with the liquid’s convective inertia playing a major role in generating steady-state levitation. We derive the physical law governing in-liquid levitation in the special case of prevailing convection effects, confirmed experimentally. We also conducted a comparative experiment showing the load-carrying capacity of the in-liquid system to be up to ten times greater than its air counterpart. By uncovering key fundamental insights, this work could potentially lead to the informed design of new in-liquid levitation systems for non-contact manipulation and friction modulation in the medical domain. |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N18.00008: Capillary imbibition in a diverging flexible channel Mouad Boudina, Gwynn J Elfring We study the imbibition of a wetting liquid between flexible sheets that are fixed on both ends. Assuming a narrow gap between the sheets, we solve the lubrication equation coupled with slender body deformation. When the sheets are parallel, we find that the deformation speeds up the flow, as shown in previous studies, but only up to the middle of the channel. The channel then contracts, increases the hydrodynamic resistance and slows down the filling process. Below a threshold stiffness, the sheets collapse and imbibition stops. We propose a scaling of the filling duration near this threshold. Next we show that if the sheets are initially tilted with a minimal angle, the channel avoids collapse. The liquid front pulls the diverging sheets and spreads in nearly parallel portions, which maintains the capillary propulsion and enhances the wicking. Therefore, while it is established that diverging rigid plates imbibe liquids slower than parallel ones, we show that elasticity reverses this principle: diverging flexible sheets imbibe liquids faster than parallel ones. We find an optimal tilt angle that gives the shortest filling time. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N18.00009: Effect of imposed shear on falling liquid films with variable fluid properties Souradip Chattopadhyay, Akshay S Desai, Hangjie Ji We present a study on the dynamics of a gravity-driven thin liquid film flow on a uniformly heated inclined plane in the presence of imposed shear stress. Based on the lubrication theory, we develop an evolution equation for the film thickness that accounts for gravity, shear stress, and temperature-dependent fluid properties. Linear stability analysis for this equation yields critical conditions for the onset of instability in long-wave perturbations. The analysis also shows the dependence of the critical Reynolds number on the direction of the imposed shear stress as well as other flow parameters. In addition, we perform a weakly nonlinear stability analysis based on the method of multiple scales and obtain a complex Ginzburg Landau equation. We observe that the film not only has supercritical stable and subcritical unstable zones, but also unconditional stable and explosive zones. Numerical simulations of the model are conducted to further investigate the spatiotemporal behavior of nonlinear waves by applying a constant shear stress in the upstream and downstream directions. Finally, we study the energy transfer from the base state to the disturbances in the presence of the imposed shear stress. |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N18.00010: Meniscus formation in soap films Ildoo Kim
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Wednesday, March 8, 2023 1:54PM - 2:06PM |
N18.00011: Use of combined electrokinetic and poiseuille flows to generate organized colloidal structures Shaurya Prakash, Varun Lochab, Ejykes Ewim Our work with combined Poiseuille and electrokinetic flows shows that particle slip velocity with respect to the fluid can be used to manipulate colloidal particles confined within microchannels. The particle migration was attributed to a new electrophoretic lift-like force that we report here, analogous to the inertial lift forces. The migration of colloidal particles towards the walls occurs for the electric potential gradient and pressure gradient in opposite directions with respect to streamwise flow, a condition we refer to as counter-flow. For dilute colloidal particle suspensions with particle diameters < 1micron, under counter-flow, led to the assembly of distinct colloidal bands within microchannels (100 – 300 wide x 34 deep x 4cm long). Band formation requires a minimum applied potential threshold at a given shear rate. Band formation is a function of particle size and volume fraction, electrolyte concentration, and the minimum electric field thresholds change non-monotonically for particle mixtures. We are able to extract these bands to porous substrates through a continuous flow microfluidic “print-head”. Here, we also discuss the effect of manipulating particle properties and fluid inertia over broad parametric ranges to elucidate robustness of particle migration to and away from microchannel walls, and the formation of particle bands in addition to their extraction and the likely parameters contributing to extracted band structures. |
Wednesday, March 8, 2023 2:06PM - 2:18PM |
N18.00012: Water entry of steel spheres in the presence of an ultra-thin elastic membrane Domenic McArthur, Varghese Mathai DOMENIC MCARTHUR, KERRY O’BRIEN, VARGHESE |
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