Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session G19: Dynamic Surface Interactions II |
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Chair: Mehdi Mortazavi, Worcester Polytechnic Institute Room: 146B |
Sunday, November 19, 2023 3:00PM - 3:13PM |
G19.00001: Unusual damping behaviour in nonlinear shape oscillations of surfactant-laden drops Debashis Panda, Lyes Kahouadji, Seungwon Shin, Jalel Chergui, Damir Juric, Omar K Matar Drop shape oscillations have received considerable attention in the literature since the earliest works of Lord Rayleigh, Sir Horace Lamb, and Chandrasekhar. It is widely understood that surfactants lower the restoring force due to surface tension and enhance the damping of such oscillations. As we show here, for the first time, via three-dimensional direct numerical simulations, however, however, the nonlinearity in the coupled surfactant-laden Marangoni stress, diminishes the damping of such oscillations over a range of system parameters. We also demonstrate via a scaling analysis the dependence of the oscillatory dynamics on the surfactant elasticity parameter in which we contrast the surfactant-free and surfactant-laden cases. This analysis captures the trends obtained from the numerical predictions. |
Sunday, November 19, 2023 3:13PM - 3:26PM |
G19.00002: Self-sustained droplet motion on gradient substrates Panagiotis E Theodorakis, Russell Kajouri, Piotr Deuar, Rachid Bennacer, Jan Zidek, Sergei Egorov, Andrey Milchev Gradient substrates can cause the motion of droplets without providing an external energy source. Here, various substrate designs will be presented, which are studied by means of extensive molecular dynamics simulations, with motion taking place in the direction of the gradient, as well as in the opposite direction. The influence of various system parameters for each system will be presented and the underlying mechanisms will be explained, anticipating that this will provide valuable information for relevant experimental designs. |
Sunday, November 19, 2023 3:26PM - 3:39PM |
G19.00003: Drops spreading and retracting and forming a rim Yotam Stern, Rafael Tadmor, Victor Multanen Surfactant laden droplets spreading on a solid may spontaneously retract due to interfacial energy gradients at the solid surface. We explain this retraction by considering fluctuations near the triple line, along with an instability due to these fluctuations and the surface gradients. We provide a theoretical description of this phenomenon along with experimental evidence. |
Sunday, November 19, 2023 3:39PM - 3:52PM |
G19.00004: Oscillations of a sessile drop driven by oblique substrate vibrations Mohammad Javad Sayyari, Dingqian Ding, Joshua B Bostwick Surface waves are formed on the surface of a sessile drop with pinned contact line when subjected to mechanical vibration, which are characterized by the mode number pair (l,m). Prior experiments by Chang et al. 2015, JFM, have shown that when the vibration is plane-normal (vertically oriented) the wave dynamics can be complex, with zonal modes (m=0) responding harmonically and non-zonal modes (m≠0) subharmonically. Particularly important are the (1,1) rocking mode and (2,0) pumping mode, as these motions are associated with the dominant horizontal and vertical center-of-mass motions, respectively, and often associated with climbing drops. We report on experiments of oblique substrate vibrations focusing on the dynamic response of the rocking mode, which can either i) respond harmonically at its resonance frequency fr or ii) respond subharmonically and mix with the harmonic pumping mode at fp =2fr. We measure the instability tongues in the driving acceleration-frequency space and show how the dominant dynamic response depends upon the orientation of the mechanical vibration. To better understand these experimental observations, we develop a theoretical model by detuning the driving acceleration, which results in an inhomogeneous Mathieu equation governing the drop oscillations. We use a perturbation method to compute the stability tongues showing qualitative agreement with both prior and current experimental results. |
Sunday, November 19, 2023 3:52PM - 4:05PM |
G19.00005: Capillary flow in open microchannels with rectangular cross-sections: a numerical study Junya Onishi Liquids in microchannels are driven by capillary force and spontaneously penetrate into the channels. Predicting and controlling such capillary-driven flow is important in various industrial fields (e.g., high-performance heat exchangers). |
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