Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session H16: Free-Surface Flows V: General |
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Chair: Palaniswamy Ananthakrishnan, Florida Atlantic University Room: 2000 |
Monday, November 24, 2014 10:30AM - 10:43AM |
H16.00001: Long-wave runup in Lagrangian framework: application to lake tsunamis Louis-Alexandre Couston, Chiang C. Mei, Mohammad-Reza Alam Coastal settlements and infrastructures are exposed and vulnerable to long waves because such waves can climb up sloping beaches without breaking. Thus accurate long-wave runup predictions are of significant importance for effective mitigation and evacuation. Although numerical models are now routinely used for long-wave propagation, calculating the runup remains an arduous task. Operational and research models usually rely on the Eulerian description of the fluid. Yet, runup processes at sloping shores can involve large horizontal stretches of the fluid domain, thereby requiring a varying number of computational nodes based on ad-hoc criteria. Here we argue that a convenient alternative is the less used Lagrangian coordinates system in which the fluid flow is described by following the trajectory of each fluid particle as an unknown function of the initial position. An immediate advantage of the Lagrangian formulation is that the free-surface and the moving shoreline become explicitly part of the solution and defined by their initial positions. As a case study we consider 3D landslide tsunamis in lakes, and present numerical results that highlight the significance of nonlinearity and wave superposition. [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H16.00002: Pressure Predictions and Run-Up on a Vertical Wall and Sloping Beach Jannette Frandsen, Caroline S\'evigny, R\'egis Xhard\'e This paper presents large scale experiments of water wave impact on wall. This study is concerned with advancing knowledge on rapidly varying pressure magnitude and distributions on different types of sea/river/harbor walls. The experiments are conducted in the new Quebec Coastal Physics Laboratory (QCPL), Canada. The flume has a depth and a width of 5 m and is 120 m long. It is designed for modeling the interactions of waves, currents and sediment transport. The wall has a test area of 1.2 $\times$ 2.4 m. The outer regions of the wall are made of steel to span the entire width of the tank. The wall is designed to behave as a rigid plate. The geometric model to full scale is about 1:4. Sensors are mounted along the flume, beach slope and wall to monitor hydrodynamics parameters. The incoming waves evolve over a flat bed to climb the final 25 m on a beach with a constant slope of 1:10. Broad- and narrow-banded spectra representing operational and storm events were investigated. The initial results are promising. Details of the underlying mechanism of various types of breaking and impact on the wall will be presented. [Preview Abstract] |
Monday, November 24, 2014 10:56AM - 11:09AM |
H16.00003: Experimental validation of a Fluid-Structure interaction model for simulating offshore floating wind turbines Antoni Calderer, Christ Feist, Kelley Ruehl, Michele Guala, Fotis Sotiropoulos A series of experiments reproducing a floating wind turbine in operational sea conditions, conducted in the St. Anthony Falls Lab. wave facility, are employed to validate the capabilities of the recently developed FSI-Levelset-CURVIB method of Calderer, Kang and Sotiropoulos (JCP 2014) to accurately predict turbine-wave interactions. The numerical approach is based on solving the Navier-Stokes equations coupled with the level set method, which is capable of carrying out LES of two-phase flows (air and water) with complex floating structures and waves. The investigated floating turbine is a 1:100 Froude scaled version of the 13.2 MW prototype designed by Sandia National Lab; it is installed on a cylindrical barge style platform which is restricted to move with two degrees of freedom, heave and pitch in the vertical plane defined by the direction of the propagating 2D waves. The computed turbine kinematics as well as the free surface elevation results are compared with the experimental data for different free decay tests and wave conditions representative of the Maine and the Pacific North West coasts. The comparison shows promising results indicating the validity of the model for simulating operational floating turbines. [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H16.00004: A 3D GPU-accelerated MPI-parallel computational tool for simulating interaction of moving rigid bodies with two-fluid flows Ashish Pathak, Mehdi Raessi We present a 3D MPI-parallel, GPU-accelerated computational tool that captures the interaction between a moving rigid body and two-fluid flows. Although the immediate application is the study of ocean wave energy converters (WECs), the model was developed at a general level and can be used in other applications. Solving the full Navier-Stokes equations, the model is able to capture non-linear effects, including wave-breaking and fluid-structure interaction, that have significant impact on WEC performance. To transport mass and momentum, we use a consistent scheme that can handle large density ratios (e.g.~air/water). We present a novel reconstruction scheme for resolving three-phase (solid-liquid-gas) cells in the volume-of-fluid context, where the fluid interface orientation is estimated via a minimization procedure, while imposing a contact angle. The reconstruction allows for accurate mass and momentum transport in the vicinity of three-phase cells. The fast-fictitious-domain method is used for capturing the interaction between a moving rigid body and two-fluid flow. The pressure Poisson solver is accelerated using GPUs in the MPI framework. We present results of an array of test cases devised to assess the performance and accuracy of the computational tool. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H16.00005: Free Surface and Flapping Foil Interactions Palaniswamy Ananthakrishnan Flapping foils for station-keeping of a near-surface body in a current is analyzed using a finite-difference method based on boundary-fitted coordinates. The foils are hinge-connected to the aft of the body and subject to pitch oscillation. Results are obtained for a range of Strouhal number, Froude number, unsteady frequency parameter $\tau$, Reynolds number and the depth of foil submergence. Results show that at low Strouhal number ($St < 0.1$) and sub-critical unsteady parameter $\tau < 0.25$, the flapping generates drag instead of thrust. At high Strouhal number and super-critical value of the unsteady parameter ($\tau > 0.25$) flapping generates high thrust with low efficiency. Thrust and efficiency are found to decrease with decreasing submergence depth of the foil. At the critical $\tau = 0.25$ and shallow submergence of the foil, the standing wave generated above the foil continues to grow until breaking; both the thrust and efficiency of the foil are reduced at the critical $\tau$. The necessary conditions for optimal thrust generation by a flapping foil underneath the free surface are found to be (i) Strouhal number in the range from 0.25 to 0.35, (ii) unsteady parameter $\tau > 0.25$ and (iii) the maximum angle of attack less than 15$^o$ for the flat-plate foil. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H16.00006: Fluid flow and the bending, buckling and wrinkling of floating elastica Finn Box, Jerome Neufeld Bending, buckling and wrinkling of floating elastic sheets may be induced by localised viscous flows leading to a complex interplay between flow and deformation. Here we present an experimental investigation illuminating the rich behaviour that arrises due to the coupling between deformation and viscous flow. An understanding of this fluid-structure interaction is applicable over a wide-range of length-scales, from the loading of the Indian subcontient by the Tibetan plateau to the deformation of nanoscale elastic sheets by fluid deposition. We explore the limits of small and large deformations through a range of fluid fluxes and by altering the ratio of spreading to ambient fluid densities, in order to characterise the bending-dominated and tension-dominated spreading regimes. We identify regimes for which the fluid motion is similar to that of a gravity current spreading over a rigid surface and for which the propagation of the fluid is dominated by the elastic deformation of the sheet. The coupling between flow and tension-induced wrinkling of the sheet, which occurs for large deformations, is also explored. [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H16.00007: New experimental technique for the measurement of the velocity field in thin films falling over obstacles Julien R. Landel, Ana Daglis, Harry McEvoy, Stuart B. Dalziel We present a new experimental technique to measure the surface velocity of a thin falling film. Thin falling films are important in various processes such as cooling in heat exchangers or cleaning processes. For instance, in a household dishwasher cleaning depends on the ability of a thin draining film to remove material from a substrate. We are interested in the impact of obstacles attached to a substrate on the velocity field of a thin film flowing over them. Measuring the velocity field of thin falling films is a challenging experimental problem due to the small depth of the flow and the large velocity gradient across its depth. We propose a new technique based on PIV to measure the plane components of the velocity at the surface of the film over an arbitrarily large area and an arbitrarily large resolution, depending mostly on the image acquisition technique. We perform experiments with thin films of water flowing on a flat inclined surface, made of glass or stainless steel. The typical Reynolds number of the film is of the order of 100 to 1000, computed using the surface velocity, the film thickness and the kinematic viscosity of the film. We measure the modification to the flow field, from a viscous-gravity regime, caused by small solid obstacles, such as three-dimensional hemispherical obstacles and two-dimensional steps. We compare our results with past theoretical and numerical studies. This material is based upon work supported by the Defense Threat Reduction Agency under Contract No. HDTRA1-12-D-0003-0001. [Preview Abstract] |
Monday, November 24, 2014 12:01PM - 12:14PM |
H16.00008: Stilling Basin Performance Analysis by ADV Sobhan Aleyasin, Nima Fathi, Peter Vorobieff The outlet flow from dams, channels, and pipes, as well as the river flow, can cause damage to the bed of the river or channel and cause scouring of structures such as the saddles of bridges, because of the huge amount of the kinetic energy carried by the flow. One of the ways to dissipate this energy is via the use of stilling basins, which are structures that calm the flow. Here we present a study of one type of stilling basins for pipe outlets based on a widely used standard1. During the study, splitters and cellular baffles were placed in the stilling basin, and their locations were changed to assess their effect on the flow dissipation. Velocity at several locations in the basin was measured via acoustic Doppler velocimetry (ADV) for different Froude numbers to investigate the effect of flow rate and inlet velocity. Based on the findings of the experiments, we make several suggestions regarding the efficiency and geometry of stilling basins. [Preview Abstract] |
Monday, November 24, 2014 12:14PM - 12:27PM |
H16.00009: Damping of liquid sloshing by foams: from everyday observations to liquid transport Alban Sauret, Francois Boulogne, Jean Cappello, Howard Stone When a liquid-filled container is set in motion, the free surface of the liquid starts to slosh, i.e. oscillate. Such effects can be observed when a glass of water is handled carelessly and the fluid sloshes or even spills over the rim of the container. However, beer does not slosh as readily, which suggests that the presence of foam could be used to damp sloshing. In this work, we study experimentally the effect on sloshing of liquid foam placed on top of a liquid bath in a Hele-Shaw cell. We generate a monodisperse 2D liquid foam and track its motion. The influence of the foam on the sloshing dynamics is characterized: 2 to 3 layers of bubbles are sufficient to significantly damp the oscillations. For more than 5 layers of bubbles, the original vertical motion of the foam becomes mainly horizontal. We rationalize our experimental findings with a model that describes the foam contribution to the damping coefficient. This study motivated by everyday observations has promising applications in numerous industrial applications such as the transport of liquid in cargoes. [Preview Abstract] |
Monday, November 24, 2014 12:27PM - 12:40PM |
H16.00010: RANS-VOF Modeling of Stratified Turbulent Flow in a Straight Rectangular Duct Chandrima Jana, Urmila Ghia, Leonid Turkevich Turbulent, stratified flow of air and water in a straight rectangular duct (aspect ratio 2:1) is investigated. Turbulent flow in straight rectangular ducts exhibits secondary currents or vortices, generated by the anisotropy of the Reynolds stresses near the boundaries. Although these secondary motions are small in comparison with the streamwise motions, they influence the flow and scalar transport, and are challenging to predict accurately. Near the two-fluid interface, the turbulence structures are modified due to their interaction with the interface. The present work simulates the two-fluid flow in the duct in order to capture the structure of the secondary vortices. The turbulent flow is modeled using a Reynolds-Averaged Navier-Stokes (RANS) formulation, along with an anisotropic Reynolds Stress Model (RSM). The air-water interface is tracked using the VOF (Volume-of-Fluid) formulation. The Reynolds stresses are tracked near the solid boundaries and in the vicinity of the air-water interface. The structure of the secondary vortices in the corner formed by the interface and the solid side wall differs from that in the corner formed by the solid duct base and the solid side wall. [Preview Abstract] |
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