Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session G05: Free-surface Flows: General |
Hide Abstracts |
Chair: William Schultz, University of Michigan Room: Georgia World Congress Center B207 |
Monday, November 19, 2018 10:35AM - 10:48AM |
G05.00001: Air cushioning in water impact -- its effect on liquid free surface Utkarsh Jain, Devaraj van der Meer, Detlef Lohse A flat plate impacting on stationary water entraps an air layer on its impacting side. This air layer, also known as air cushion, deforms the liquid free surface before the moment of impact. We use high-speed imaging and a new technique to measure the free surface deformation caused by this air cushion close to the moment of impact. This intervening air layer is a low-pressure region, which causes the free surface to be pulled upwards towards the plate due to Bernoulli suction. Our observations are qualitatively well reproduced by two-fluid boundary integral simulations. We attempt to explain the upwards suction of the free surface, and other experimentally observed features using potential flow theory and boundary integral simulations. Our observations have significance for air-pocketing in the water-impact problem which influences the consequently generated loads. |
Monday, November 19, 2018 10:48AM - 11:01AM |
G05.00002: CFD Validation Studies of Slamming Pressures During Wedge Drop Impact Mark Fenn, Maysam Mousaviraad, Christine Ikeda-Gilbert Impact loads due to slamming are one of the critical design issues for high-speed planing crafts. CFD validation for slamming loads is presented in this work using wedge drop experimental data. Two different sets of experiments are used: 10° deadrise angle drops by Carderock, and 20° deadrise experiments carried out at USNA. Both experiments use rigid structures and measure high-frequency pressure data at different locations on the wedge bottom. Uncertainty analyses of the repeated experiments are carried out for the peak pressure values. CFD uncertainties are quantified through systematic time-step verification studies. Validation studies are carried out by comparing the simulation error values with the validation uncertainty intervals defined by combining the experimental and the simulation numerical uncertainties. The results from current OpenFoam CFD simulations are compared with the previous simulations against the 10° deadrise experiments using five different CFD solvers ranging from potential flow to URANS/LES solvers. A summary of the state of the art is provided including the grid sizes and the computational cost requirements. The next step after the current rigid structure studies will include the FSI validation studies against flexible bottom wedge drop experiments. |
Monday, November 19, 2018 11:01AM - 11:14AM |
G05.00003: Dynamics of a thin film driven by a moving pressure source Davin Lunz, Peter D. Howell Motivated by the liquid metal coating on a divertor in a tokamak, we investigate the flow of a thin film of incompressible fluid on an inclined substrate subjected to a localised external pressure that oscillates parallel to the substrate. When the movement of the pressure occurs on a time scale significantly longer than the characteristic time for the thin film to equilibrate, the system is quasi steady. In the opposite extreme, where the pressure oscillates much faster than the response time of the free surface, a multiple scales analysis shows that the free surface is exposed to an effective time-averaged pressure profile. Thus the oscillations can act to spread the momentum load of the applied pressure, resulting in smaller deformations of the liquid film. |
Monday, November 19, 2018 11:14AM - 11:27AM |
G05.00004: Asymptotic theory of wetting transition in dip coating Jian Qin, Peng Gao When a plate is withdrawn from a liquid bath up to a sufficiently large speed, the capillary force fails to compete with the viscous drag, leading to the entrainment of liquid films. This wetting transition has been theoretically understood at small equilibrium contact angles. For a more general case where the viscosity ratio of two fluids and the contact angle are almost arbitrary, we demonstrate that this problem can always be formally reduced to the simpler above-mentioned problem through an appropriate mathematical transformation. Both the dragging and pushing problems can be treated under this approach. By this means, we obtain the critical plate speed for the onset of wetting transition. Moreover, we build a connection between the Cox-Voinov law and the classical lubrication theory for moving contact lines. |
Monday, November 19, 2018 11:27AM - 11:40AM |
G05.00005: Wettability-confined liquid-film convective cooling: Parameter study Theodore P Koukoravas, Pallab Sinha Mahapatra, Ranjan Ganguly, Constantine M Megaridis An experimental investigation is conducted on the cooling of a metallic heat spreader of O(10 cm2) area with an embedded millimeter-size heat source. Specifically designed wettability patterns featuring wedge-shaped wettable tracks on the heat spreader divert an orthogonally-impinging water jet providing necessary cooling. Capillary-driven, directional, free-surface transport of the coolant is accomplished for several centimeters on the heat spreader. Sensible heat transfer is evaluated at different flow rates for various patterns and heat source to heat spreader relative positioning. Marangoni stresses arising from temperature gradients oppose the free-surface flow under certain conditions. Strategies to overcome the detrimental effects of such thermocapillary stresses are explored and analyzed in terms of cooling performance. Fundamental flow and track design parameters are explored in pursuit of increased performance and Marangoni-resilient wettability patterns. Heat removal rates of the order of 100 W/cm2 are attained without phase change at coolant flow rates as low as ~1 mL/s and heat source superheats of 65oC. The present approach opens up new opportunities for heat removing devices that rely on advective cooling facilitated by wettability-patterned metal substrates. |
Monday, November 19, 2018 11:40AM - 11:53AM |
G05.00006: Dripping of a suspended thin viscous film Fan Yang, Jens Eggers, Lailai Zhu, Howard A. Stone Thin viscous films are ubiquitous in nature and industry, such as bubble draining, polymer processing and glass manufacturing. In this report, we investigate, both experimentally and numerically, the sagging and dripping of a thin viscous film due to gravity, which is suspended in air and hinged at the rim. Initially the bending forces dominate in the film; for intermediate times, the stretching forces become more significant as the deformation of the film increases; at late times a “blob” forms at the center of the film due to thickening and detaches from the film. Then, the film recovers the intermediate-time behavior and starts another cycle until it breaks up due to the loss of mass from dripping at the center. Our model incorporates both gravity and surface tension effects and the numerical results are in good agreement with the experiments. |
Monday, November 19, 2018 11:53AM - 12:06PM |
G05.00007: Modified capillary rheometry procedures for low viscosity liquids Subramaniam Balakrishna, William Schultz We extend the range of the traditional capillarity breakup rheometer with oscillatory deformation profiles that avoid breakup. When used in conjunction with the differential analysis of McCarroll et al. (2016), oscillatory deformation will allow eventual characterization of viscoelastic properties. For Newtonian fluids, the midfilament radius histories are relatively independent of the filament Ohnesorge number, Oh, while the second derivative of curvature characterizes Oh. Using numerical simulations, we investigate the validity of the one-dimensional approximation and the sensitivity to experimental resolution in the Oh-frequency-amplitude-aspect ratio parameter space. |
Monday, November 19, 2018 12:06PM - 12:19PM |
G05.00008: Do drop-impact craters produce singular jets? Sigurdur T Thoroddsen, Kohsei Takehara, N. D. Nguyen, T. G. Etoh Drop-impact craters rebound and usually produce prominent Worthington jets. For a limited range of drop-impact Weber numbers, capillary waves travel down the crater surface and a dimple forms at the bottom of the crater. This dimple can pinch off and entrap a bubble into the pool, in a process call regular bubble entrapment. This bubble oscillates and emits sound. This parameter range is also associated with the appearance of high-speed fine jets. It has been suggested that the fastest jets are driven by a singularity in the surface curvature at the bottom of the dimple. Herein we use two ultra-high-speed video cameras to simultaneously image the jetting and the dimple evolution*. Our imaging at micro-second resolution never shows any curvature singularity at the bottom of the dimple. Furthermore, the fastest jets emerge when the inertial focusing drives the jet without pinch-off of a bubble. In contrast the bottom dimple air-cylinder is pushed up at high velocity when its diameter is of the order of 25 microns, producing jets which emerge at speeds as fast as 50 m/s. *Thoroddsen et al., J. Fluid Mech., 848, R3 (2018). |
Monday, November 19, 2018 12:19PM - 12:32PM |
G05.00009: Investigation of the Film Thickness of the Wall Flow created by the impingement of a free-surface liquid Jet Joern R Wassenberg, Peter Stephan, Tatiana Gambaryan-Roisman Liquid jet impingement is used in industry when surfaces must be cooled or cleaned, because it’s high heat or mass efficiency, respectively. The film thickness and velocity distribution as well as the flow regime in the zone surrounding the impingement point and confined by the hydraulic jump are of high interest, since they govern the heat and mass transport and thereby determine the jet impingement performance. In the present work, the horizontal impingement of a free-surface liquid jet onto a vertical substrate is investigated at jet Reynolds numbers of 20,000 to 50,000, with nozzle sizes of 3 and 4 mm different nozzle types (pipe or convergent), and various nozzle to plate distances. The impinging jets show surface disturbances, that origin in turbulence flow inside the nozzle as well as in Kelvin-Helmholtz instability. These surface disturbances and the internal flow have a strong influence on the local film thickness distribution in the wall flow, which is measured along the radial axis from the impingement point using Chromatic Confocal Spectroscopy. |
Monday, November 19, 2018 12:32PM - 12:45PM |
G05.00010: The effects of curvature on flow structure in river bends Oladapo T Aseperi, Karan Venayagamoorthy In this study, the focus is on understanding the effect of curvature on the three-dimensional flow structure in a channel bend using large-eddy simulations. A key non-dimensional geometric parameter that influences the flow structure is the ratio of the radius of curvature to the top width of the uniform flow upstream of the bend R/Tw. Four highly-resolved large-eddy simulations of 180o bends were performed with R/Tw. ranging from 1.25 to 8.7, encompassing tight to mild bends. Analysis of simulation results show that on average, the maximum shear stresses for tight bends are closer to the inner bank and shift closer to the outer bank in the interior of the channel bend. Furthermore, it is clear that the flow structure evolves from the beginning of the bed to a more developed condition beyond 90o into the bend. This research is aimed at contributing towards fundamental understanding of the flow structure in river bends using computational simulations. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700