Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session R18: Microscale and Nanoscale Flows: Oscillations and Streaming |
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Chair: Jaime Juarez, Iowa State University Room: 250 B |
Monday, November 25, 2024 1:50PM - 2:03PM |
R18.00001: Abstract Withdrawn
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Monday, November 25, 2024 2:03PM - 2:16PM |
R18.00002: Multiphase MicroMixer Oscillator Filip Horvath-Gerber, Lyes Kahouadji, Seungwon Shin, Jalel Chergui, Damir Juric, Omar K Matar We present anumerical study of a microchannel device called 'heart-spade' or'Corning Micro-Mixer', shedding light on a "multiphase fluidic oscillator" which is an emergent property of theflow over a certain range of parameter values. This behaviour, distinct from the well-known interfacial regimes,such as jetting or dripping, arises due to a non-symmetrical pinching mechanism which accompanies the flow.Despite the symmetric configuration of the Corning MicroMixer channel, and the symmetric implementation ofthe inlet boundary conditions in a fully three-dimensional and massively-parallelized,direct numerical simulation code, intriguing oscillatory motion emerges and dominates the dynamics. |
Monday, November 25, 2024 2:16PM - 2:29PM |
R18.00003: Frequency-dependent streaming flows from acoustically actuated bubbles and sharp edges Ritu R Raj, Ankur Gupta, C. Wyatt Shields IV Acoustic streaming is used to produce fluid flows for applications such as mixing in microfluidics and propulsion in microrobotics. Typically, acoustically responsive structures, such as a bubbles and sharp edges, generate streaming by vibrating when excited with an acoustic field. To date, most work has focused on building microscale systems with a single type of acoustically responsive structure actuated at its primary resonance frequency. In this work, we develop a joint computational/experimental framework to predict the frequency-dependent streaming flows produced in systems with more than one type of acoustically responsive structure, each with its own resonance behavior. Experimentally, we fabricated bubbles and sharp edges with two-photon lithography, used piezoelectric transducers to acoustically excite the structures, visualized the flows using confocal microscopy, and measured the flow fields with microparticle image velocimetry. We quantitatively compared these results with numerical predictions from a perturbation theory model of streaming. We then used eigenfrequency analyses of the bubble and sharp edge vibrations to interpret the frequency response of the fluid flows. Using these measurements, we predicted the frequency dependence of the fluid flows produced by a microparticle that has both a bubble and a sharp edge. This work provides a framework to predict and control the streaming flows produced in systems containing multiple acoustically responsive structures.
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Monday, November 25, 2024 2:29PM - 2:42PM |
R18.00004: Steady Streaming and Pumping Driven by Two Frequency Oscillations Hyun Lee, Robert D Guy, William D Ristenpart Past experiments showed net transport of an object sliding on a surface undergoing two mode vibrations for certain frequency pairs. Specifically, when the vibrations satisfied a non-antiperiodic waveform, net motion was seen. Inspired by these experiments, we look for a fluid analogue and revisit the classical problem of steady streaming in fluids (i.e., nonzero mean flow produced by a periodic forcing) driven by multifrequency oscillations. Using numerical simulations, we examine the flow generated by two-frequency oscillations of a rigid object immersed in fluid. Like the experiments, our results show that net pumping occurs when these two-frequency pairs produce a non-antiperiodic driving force. Furthermore, we use small amplitude analysis and extend the past results of steady streaming to the two-frequency case. While steady streaming occurs at second order in amplitude, pumping is a higher order effect which is analytically challenging to compute. Because pumping is a higher order effect, we use a hybrid numerical and analytical method to explain the mechanism behind pumping of two-frequency oscillations. For example, when the frequency ratio is two, pumping is a third order effect in amplitude, and we further generalize our analysis to different frequency ratios. |
Monday, November 25, 2024 2:42PM - 2:55PM |
R18.00005: Theory and simulation of elastoinertial rectification of oscillatory flows in deformable rectangular channels Uday M Rade, Shrihari D Pande, Ivan C. Christov A slender 2D channel with a rigid bottom wall and an elastic top wall deforms when a fluid flows through it. Hydrodynamic forces cause the elastic wall's deformation, and deformation causes a change in the cross-sectional area that affects the hydrodynamic forces, representing a two-way coupled fluid-structure interaction (FSI). Few studies have analyzed this nonlinear regime of oscillatory flows in deformable 2D channels despite the broad spectrum of bio and microfluidic applications. Because of the nonlinear coupling between flow and deformation and the attendant asymmetry in the geometry caused by this FSI, a streaming (cycle-averaged) pressure is generated by a time-periodic oscillatory forcing of the flow. In a rigid channel, the cycle-averaged pressure is expected to vanish, but wall elasticity and flow inertia lead to "elastoinertial rectification'' in a deformable channel [Zhang & Rallabandi, arXiv:2404.02292]. By extending Zhang & Rallabandi's theory of axisymmetric tubes to rectangular channels and via new direct numerical simulations, we examine the cycle-averaged pressure as a function of the Womersley, the elastoviscous, and the compliance (FSI) numbers. We conduct simulations using an arbitrary Lagrangian-Eulerian (ALE), i.e., conforming, FSI formulation with SUPG stabilization implemented in FEniCS. For small compliance numbers, we find a good agreement between simulations and theory. |
Monday, November 25, 2024 2:55PM - 3:08PM |
R18.00006: Pressure Distribution of Oscillatory Flows in Compliant 3D Channels Anxu Huang, Shrihari D Pande, Ivan C. Christov, Jie Feng Deformable microchannels emulate a key characteristic of soft biological systems and flexible engineering devices: the fluid-structure interaction (FSI) between internal flow and a compliant boundary. Elucidating FSI in oscillatory flows in such systems is important for understanding mixing/transport enhancement as well as physiological flows. Here, we investigate the time-varying pressure distribution in a canonical geometry of a 3D rectangular channel with a deformable top wall. Based on the recent approach of Zhang and Rallabandi (arXiv:2404.02292), we derive the leading-order pressure profiles for Newtonian fluid in such a wide, compliant 3D channel under the lubrication approximation. Unlike rigid conduits, the pressure distribution is not linear with the axial coordinate. To validate this prediction, we further design a high-precision experimental platform with a speaker-based flow-generation apparatus and a pressure acquisition system with multiple axial ports. The experimental measurements show good agreement with the predicted pressure profiles across a range of the key dimensionless quantities: the Womersley number, the compliance number, and the elastoviscous number. Finally, we explore the nonlinear FSI coupling beyond the leading order by examining nonlinear streaming effects (rectification of the oscillatory flow) via the cycle-averaged pressure. |
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