Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session E32: Drops: Impact Interactions |
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Chair: Mahesh Bandi, Okinawa Institute of Science and Technology Room: 313 |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E32.00001: Modeling drop impacts on inclined flowing soap films Saikat Basu, Ali Yawar, Andres Concha, Mahesh Bandi Small drops impinging on soap films flowing at an angle primarily exhibit three fundamental regimes of post-impact dynamics: (a) the drop bounces off the film surface, (b) it coalesces with the downstream flow, and (c) it pierces through the film. During impact, the drop deforms along with a simultaneous, almost elastic deformation of the film transverse to the stream direction. Hence, the governing dynamics for this interaction present the rare opportunity to explore the in-tandem effects of elasticity and hydrodynamics alike. In this talk, we outline the analytical framework to study the drop impact dynamics. The model assumes a deformable drop and a deformable three-dimensional soap film and invokes a parametric study to qualify the three mentioned impact types. The physical parameters include the impact angle, drop impact speed, and the diameters of the drop prior to and during impact when it deforms and spreads out. Our model system offers a path towards optimization of interactions between a spray and a flowing liquid. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E32.00002: Experimental study of drop impacts on soap films Ali Yawar, Saikat Basu, Andres Concha, Mahesh Bandi Impinging drops on flowing and static soap films demonstrate at least three distinct types of impact regimes: (a) the drop bounces off the film surface, (b) it coalesces with the downstream flow for a moving film and for static films it gets assimilated within the film, and (c) it pierces through the film. The interaction presents a unique opportunity to explore the impact of a quasi one-dimensional object on a two-dimensional fluid, much like a comet impacting on a thin atmosphere. We present a detailed experimental study of droplet impacts on soap film flow, for a number of film inclination angles and falling heights of the drop. Imaging techniques employed include sodium lamp interferometry to measure film thickness fluctuations and particle tracking velocimetry to measure the velocity field. Film thickness measures approximately 10 microns and the drop diameter is 1 mm. We mostly observe the bouncing-off regime for smaller inclination angles. However, at higher impact angles, puncturing of the film becomes a more common occurrence. We show that when the drop bounces off the film, there is a momentum transfer leading to vortex dipole shedding, along with the generation of capillary waves; an impulsive regime that may share correspondence with the locomotion of water striders. [Preview Abstract] |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E32.00003: Large bubble entrainment in drop impact Marie-Jean Thoraval, Yangfan Li, Sigurdur T. Thoroddsen A drop impacting on a pool of the same liquid can entrap air bubbles in many different ways. A peculiar entrapment was observed by Pumphrey and Elmore (1990) and remained unexplained until now. For a small range of parameters, the cavity produced by the impacting drop spreads radially in a dish-shape and then closes to entrap a bubble larger than the drop. We demonstrate that the large bubble is caused by a vortex ring produced in the liquid during the impact of the drop. We combine experiments and numerical simulations to show that the vortex ring pulls on the interface on the side of the cavity to stretch it radially, explaining the shape of the cavity. Only prolate drops are able to generate large bubbles. This is due to the self-destruction of the vortex earlier during the impact for flatter drops. [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E32.00004: Droplet impact on a liquid pool and bubble entrainment for low Bond numbers Pascal Sleutel, Pei Hsun Tsai, Wilco Bouwhuis, Marie-Jean Thoraval, Claas-Willem Visser, An-Bang Wang, Michel Versluis, Detlef Lohse Droplets impacting on a pool of liquid and the subsequent bubble entrainment has been well studied for high Bond numbers where the droplets size is large and velocities are low. Here we study for the first time the droplet impact and bubble entrainment in an entirely new parameter regime (Bo $\sim$ $10^{-2} - 10^{-3}$, U $\sim$ 6-20 m/s, D $\sim$ 0.08-0.4 mm). We follow up on the pioneering work of Oguz {\&} Prosperetti, now in the surface tension dominated regime. We predict the bubble entrainment zone by balancing movement of the cavity bottom and droplet inertia with capillary waves enclosing the bubble. Both high-speed imaging experiments and numerical simulations in Gerris validate the model and show the importance of air for smaller droplet sizes. [Preview Abstract] |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E32.00005: Drainage of the air film during drop impact on flowing liquid films Zhizhao Che, Omar Matar Immediately upon the impact of a droplet on a liquid or a solid, a thin air cushion is formed by trapping air beneath the droplet. The drainage of the air film is critical in determining the eventual outcome of the impact. Here we propose a model to study the drainage of the gas film between a droplet and a flowing liquid film. The effects of a wide range of parameters influencing the drainage process are studied, such as the fluid viscosities, the surface tension, the velocity of the droplet, the velocity of the liquid film. The results show that the tangential movement of the liquid film can delay the drainage of the air film and promote the bouncing of droplets. This confirms our previous experimental results, which show that during the impact of droplets on flow liquid films, the probability of bouncing increases with the Reynolds number of the liquid film. [Preview Abstract] |
Sunday, November 22, 2015 5:55PM - 6:08PM |
E32.00006: Ripple Dynamics of Water Entry after Pinch Off Austin Mituniewicz, Brian Chang, Matt Crosson, Sunghwan Jung Most research concerning water entry of a projectile focuses on splash during impact and air entrainment during descent. Following pinch off, the air cavity shortens and interfacial rippling develops. In this study, we examine ripple formation induced by projectiles of different shapes under varying kinematic conditions. The amplitude and wavelength of these ripples is determined by the geometry and kinematics of the projectile as well as the cavity pressure. Observations of ripple dynamics demonstrate a close in-phase relationship between the force acting on the projectile and the pressure within the air cavity itself. [Preview Abstract] |
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