Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session L31: Free-Surface Flows III |
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Chair: John McHugh, University of New Hampshire Room: 402 |
Monday, November 25, 2013 3:35PM - 3:48PM |
L31.00001: Experimentally observed flows inside inkjet-printed aqueous rivulets Vadim Bromberg, Timothy Singler Understanding the flow inside sessile liquid masses of different shapes is important in a variety of solution-based material deposition and patterning processes. We investigated the shape evolution and internal flow of inkjet-printed aqueous rivulets of finite length using optical microscopy. Rivulets were formed by printing a pre-determined number of drops at controlled frequency and spatial overlap. Capillary-driven rivulet breakup into individual drops was inhibited by chemical modification of substrates that resulted in controlled contact angle hysteresis with zero static receding contact angle. A variety of novel capillary- and evaporatively-driven flows were identified using fluorescent particles as flow tracers. Flow regimes were investigated as a function of advancing contact angle, deposition parameters, and fluid properties. [Preview Abstract] |
Monday, November 25, 2013 3:48PM - 4:01PM |
L31.00002: Investigation of bubble entrainment by breaking waves in turbulent two-phase Couette flows Dokyun Kim, Ali Mani, Parviz Moin The bubbles entrained by breaking waves have an important role in understanding the upper-ocean physical processes. Although the size distribution of bubbles is most important in these processes, its characteristics have not been clearly understood because measurement of the bubble size is challenging especially in the high void-fraction region. In the present study, numerical simulations are performed to investigate the bubble formation mechanism in breaking waves of turbulent two-phase flow with moving side-walls. A newly developed conservative VOF method$^{2}$ coupled to a subgrid Lagrangian breakup model is used to resolve wave breakup phenomenon and resulting bubbles. The numerical method is tested and validated against the experiments for canonical problems. The Reynolds and Froude numbers considered are 12,760 and 6.8, respectively. In order to investigate the effect of Weber number on the characteristics of the bubble size, the simulations are conducted for two different Weber numbers. The statistics and scale properties of bubbles will be presented and discussed. [Preview Abstract] |
Monday, November 25, 2013 4:01PM - 4:14PM |
L31.00003: Free-surface flow driven by a deforming boundary Frederik Brasz, John Lister, Craig Arnold We present an analytical solution for flow in a liquid layer driven by a deforming boundary. An initially flat wall undergoes a sinusoidal deformation with small amplitude relative to wavelength, imparting momentum to the fluid. Initially, the flow is directed away from the crests and slows with the slowing of the boundary motion. A domain perturbation method is used to reveal that even when the boundary stops moving, nonlinear interactions with the free surface leave a remnant momentum, and this momentum is directed back toward the crests, a precursor to jet formation. This scenario arises in a laser-induced printing technique in which an expanding blister imparts momentum into a liquid film to form a jet. This analysis provides insight into the physics underlying interactions between deforming boundaries and free surfaces, in particular the dependence on the thickness of the liquid layer relative to the deformation wavelength. Numerical simulations are used to verify the theory and show its range of validity. [Preview Abstract] |
Monday, November 25, 2013 4:14PM - 4:27PM |
L31.00004: Numerical simulation of a turbulent wall jet in a rough-bed open channel Joongcheol Paik, Fabian Bombardelli, Ken Loh Numerical results of the mean flow and turbulence characteristics in the near field of a turbulent plane wall jet issuing from a sluice gate onto a rough flat wall are presented. The flow had been experimentally investigated by Albayrak et al. [I. Albayrak, E.J. Hopfinger and U. Lemmin, J. Fluid Mech., 606, 27, (2008)] at the Reynolds number of 33,500 and the Froude number of 1.014, based on the jet velocity and the sluice gate opening height. Turbulent flow is simulated using the $k$-$\omega$ shear-stress transport (SST) model and the scale-adapted simulation (SAS) based on the SST model. The jet velocity profile is numerically reproduced based on the difference of upstream and downstream water levels computed by the volume of fluid method. The numerical results show that the outlet boundary should be carefully treated to successfully reproduce the velocity profile approaching the shape of the typical open-channel flow downstream of the attachment point of the jet. Numerical solutions appear to agree reasonably well with the measurement in terms of the outer-layer spatial growth rate and Reynolds stress distributions. The mesh convergence of numerical solutions is also presented. [Preview Abstract] |
Monday, November 25, 2013 4:27PM - 4:40PM |
L31.00005: Dispersive Hydrodynamics in Viscous Fluid Conduits Nicholas Lowman, Mark Hoefer The evolution of the interface separating a conduit of light, viscous fluid rising through a heavy, more viscous, exterior fluid at small Reynolds numbers is governed by the interplay between buoyancy and viscous stress. Perturbations about a state of vertically uniform, laminar conduit flow are considered in the context of the Navier-Stokes equations with appropriate boundary conditions, which lead systematically to a maximal balance between buoyancy driven, nonlinear self-steepening and viscous, interfacial stress induced, nonlinear dispersion. This results in a scalar, nonlinear partial differential equation describing large amplitude dynamics of the cross-sectional area of the intrusive fluid conduit. Unsteady perturbations of the uniform state have been shown in a laboratory setting to produce hallmark features of nonlinear, dispersive systems including solitary waves and nonlinear wave trains, i.e. dispersively regularized shock waves (DSWs). Shock waves solutions to the conduit equation for step-like initial data exhibit novel DSW behaviors, including backflow and DSW implosion. The asymptotic analysis shows that these fully nonlinear, dispersive hydrodynamic features of the reduced model are experimentally accessible in viscous fluid conduits. [Preview Abstract] |
Monday, November 25, 2013 4:40PM - 4:53PM |
L31.00006: Free surface waves on a horizontal shear Gary Lapham, John McHugh Free surface waves on a non-uniform mean flow are considered. The mean flow $U(y)$ varies with the transverse coordinate $y$ but not the vertical. The domain is bounded on one side by a flat rigid vertical wall and unbounded on the other side. The mean flows considered are nonzero near the vertical wall and approach zero far from the wall, e.g. $U = {e^{- \gamma y}}$. For large $y$ where the mean flow is near-zero the waves are merely irrotational Stokes' waves. Near the wall the mean flow and the waves are rotational but still inviscid. Linear solutions are obtained for several canonical cases with a nonuniform coordinate transformation that converts the free surface boundary condition into a Bessel equation. A Bessel expansion provides the velocity components, then wavespeeds are obtained numerically. Steady waves are found with wavespeeds outside the range of $U$, matching previous results in a flow bounded on both sides. [Preview Abstract] |
Monday, November 25, 2013 4:53PM - 5:06PM |
L31.00007: CFD Experiments for Wind-Turbine-Platform Seakeeping Models and Flow Physics Alexander Dunbar, Eric Paterson, Brent Craven, James Brasseur As part of the Penn State ``Cyber Wind Facility,'' we describe the development and application of a tightly-coupled CFD/6-DOF solver in OpenFOAM for the simulation of offshore floating wind turbine platforms. We highlight the tightly-coupled computational framework and validation of the solver via a comparison with benchmark experimental measurements. The validated CFD/6-DOF solver is then applied to the OC4 DeepCwind semisubmersible for the prediction of platform motion due to wind and wave loading. Supported by the US Department of Energy. [Preview Abstract] |
Monday, November 25, 2013 5:06PM - 5:19PM |
L31.00008: Flow past a cylinder near a free surface Keegan Delaney, Marcos Vanella, Elias Balaras, Amir Riaz Flow past a cylinder close to a free surface gives rise flow phenomena that are very different from ones in cases where the cylinder is fully submerged. In this study we will report resolved large-eddy simulations, where we examine the effects of various parameters that have been shown to effect the flow phenomena in previous experimental studies. In all computations a Navier-Stokes solver for multiphase incompressible flows with immersed boundaries and Adaptive Mesh Refinement is utilized. It employs level-set techniques to sharply define the interface between different phases. A fractional step method is used to solve the momentum and continuity equations, which results in a variable coefficient Poisson pressure equation. Proper jump conditions are applied to the Poisson pressure equation to accurately capture the jump in pressure that results from surface tension between different phases. Scalability and efficiency were placed at a premium during development of the solver, which has been tested to core counts on the order of 10,000. We will present details on the interactions between the free surface and vortices shed from the cylinder and their impact in the structure of the immediate wake and air entrainment. [Preview Abstract] |
Monday, November 25, 2013 5:19PM - 5:32PM |
L31.00009: Universal Froude number in a circular hydraulic jump, implication on the jump radius selection Alexis Duchesne, Luc Lebon, Laurent Limat In the literature, it is known that the properties of a standard hydraulic jump depend critically on a Froude number Fr defined by the ratio between the flow speed and the gravity waves speed: Fr is larger than 1 upstream of the shock, and smaller than 1 downstream, an accumulation of gravity waves occuring at the shock with formation of a sharp liquid wall. Surprisingly, to our knowledge, this question of Froude number value has never been explored for the circular hydraulic jump formed by an impinging jet on a horizontal surface. We have investigated carefully this question, varying the flow rate, the liquid viscosity and the surface tension. We have found that, in the specific case of a circular jump with no confinement walls, there exists an universal value, equal to 0.38 on which the Froude number defined at the jump exit is locked. We examine the implications of this result on the selection of the jump radius R, after combining it with the large scale flow structure around the jump, calculated in the lubrication limit. In agreement with our data, R is very close to follow the law proposed by Bohr, but this law has to be modified by introducing non negligible logarithmic corrections.We also discuss the implications of our results in terms of Watson description of the shock. [Preview Abstract] |
Monday, November 25, 2013 5:32PM - 5:45PM |
L31.00010: SPH Simulation of Liquid Scattering from the Edge of a Rotary Atomizer Seiichiro Izawa, Takuya Ito, Masaya Shigeta, Yu Fukunishi Three-dimensional incompressible SPH method is used to simulate the behavior of liquid scattering from the edge of a rotary atomizer. Rotary atomizers have been widely used for spraying, painting and coating, for instance, in the automobile industry. However, how the spray droplets are formed after leaving the edge of the rotary atomizer is not well understood, because the scale of the phenomenon is very small and the speed of rotation is very fast. The present computational result shows that while the liquid forms a film on the surface of the rotating disk of the atomizer, it quickly deforms into many thin columns after leaving the disk edge, and these columns soon break up into fine droplets which spread out in the radial direction. The size of droplets tends to become smaller with the increase in the disk rotating speed. The results show good agreement with the experimental observations. [Preview Abstract] |
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