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 R11: Waves III: Nonlinear Waves and Turbulence |
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Chair: Fabrice Veron, University of Delaware Room: 3007 |
Tuesday, November 25, 2014 1:05PM - 1:18PM |
R11.00001: Turbulent dynamics of breaking internal gravity waves on slopes Robert Arthur, Oliver Fringer The turbulent dynamics of breaking internal gravity waves on slopes are investigated using a high-resolution numerical model. A Navier-Stokes code is employed in an idealized, three-dimensional domain where an internal solitary wave of depression impinges upon a sloping bottom. A bottom-following curvilinear grid is used to capture the bathymetry accurately, and the vertical grid spacing $\Delta $z$^{\mathrm{+}}=$O(1) near the bottom in the breaking region to resolve the near-wall flow. In order to understand the transition to turbulence as a result of wave breaking, flow variability is analyzed in the cross-stream dimension. In particular, streamwise vorticity, or secondary streamwise rolls that lead to the turbulent breakdown of the wave, is found to develop in regions of unstable stratification. Dissipation and irreversible mixing of the density field are analyzed as a function of time, and related to breaking dynamics; irreversible mixing is quantified in terms of the change in background potential energy inside the domain. The mixing efficiency is also calculated for various wave and slope conditions. These results have application to the nearshore coastal ocean, where breaking internal waves affect the distributions of ecologically important scalars such as temperature, oxygen, and nutrients. [Preview Abstract] |
Tuesday, November 25, 2014 1:18PM - 1:31PM |
R11.00002: Modeling the damping rates of surface water waves Girish Kumar Rajan, Diane Henderson In this work, we investigate linear damping rates of surface water waves in both laboratory and ocean settings. We formulate two models that generalize previous work to include the effects of air and two interfacial conditions. The first is a two-fluid model (representing air and water) with a monomolecular film at the interface. The second is a three-fluid model that has a Newtonian fluid with variable, but thin, thickness at the interface of the water and air. Limiting cases of these models reduce to expressions that agree with previously published results. We compare predictions of damping rates to both laboratory and oceanographic data. These models have been developed for a general fluid system and may thus be used for fluids other than air and water, with any general fluid-film at the interface, whose properties are known. [Preview Abstract] |
Tuesday, November 25, 2014 1:31PM - 1:44PM |
R11.00003: Large Eddy Simulation of Disturbance Waves and Heat Transfer in Annular Flows Geoff Hewitt, Junfeng Yang, Omar Matar A numerical method for forced convective boiling in an annulus needs to be developed in order to elucidate the reason for nucleation enhancement by disturbance waves. The benchmark test case is the experiment of Barbosa et al., in which nucleate boiling in a liquid film, droplet entrainment, disturbance waves of the liquid film, and their interaction were observed. We first develop a numerical strategy to model the development of disturbance waves in annular flows in which the highly turbulent gas core flow drives the laminar liquid flow upwards using advanced CFD tool TransAT. Then, the heat transfer process in the non-boiling annular flow was investigated to provide insight into the temperature gradient underneath the wave region. Agreement with experimental data for the temperature field could be improved by accounting for phase change in the models. However, the modelling results are still indicative and show that heat transfer is hindered in the wave region. The local overheat zones underneath the disturbance wave could play key roles activating the nucleation boiling sites. [Preview Abstract] |
Tuesday, November 25, 2014 1:44PM - 1:57PM |
R11.00004: The Turbulent Wake and Internal Wave Field Due to a Sphere Moving in an Ocean Thermocline Laura Brandt, James Rottman, Cecily Taylor, Dave Broutman We use ray theory to gain insight into the generation and propagation of internal waves produced by a sphere towed horizontally at constant speed in an idealized ocean thermocline. In particular, we seek to test a previously proposed model of internal wave generation produced by the flow over the body and the disturbances produced by the turbulent wake within the framework of a ray model of the internal waves. This model approximates the stratified flow over the sphere as a combination of a distribution of sources representing the steady internal wave flow, relative to the sphere, and a vertically oscillating sphere, representing the waves generated by the turbulent eddies in the wake. The frequency of oscillation of the sphere is based on laboratory observations of the frequency of shedding of coherent structures in the wake. We formulate a ray model of this flow that incorporates the source distribution as the initial conditions of the internal wave rays produced by the sphere. The results of our simulations are compared with laboratory experiments. The steady wave flow is well represented by this model, in agreement with previous studies. The model of the generation of the unsteady waves, which until now have been untested, requires some additional tuning of the parameters. [Preview Abstract] |
Tuesday, November 25, 2014 1:57PM - 2:10PM |
R11.00005: Thermo-electrohydrodynamic internal waves in annular geometry Harunori Yoshikawa, Antoine Meyer, Olivier Crumeyrolle, Innocent Mutabazi An electric field applied to a dielectric fluid with a temperature gradient generates a body force on the fluid, which can be regarded as thermal buoyancy associated with an electric effective gravity. We consider the internal waves due to this thermoelectric force in annular geometry, where the force field is centro-symmetric. The Earth's gravity is neglected. This configuration is of relevance to large-scale geophysical flows. The dispersion relation of the waves is determined by a spectral method, with or without taking into account the fluid viscosity. The effects of geometry curvature and of a thermoelectric feedback are discussed. The oscillatory instability of the circular Couette flow under the thermoelectric body force and its relation with the waves will also be discussed. [Preview Abstract] |
Tuesday, November 25, 2014 2:10PM - 2:23PM |
R11.00006: Experiments on the interaction between hydrodynamic turbulence and surface waves Timothee Jamin, Michael Berhanu, Eric Falcon Different regimes of interaction between hydrodynamic turbulence and a free surface are investigated in a meter scale basin. A homogeneous and isotropic turbulence is generated by an 8x8 array of jets pointing upwards at the bottom of the tank. The 64 jets are driven individually to reach a random spatiotemporal forcing pattern and produce an intense turbulence. Using fluid velocity measurements, we characterize the turbulence obtained with this setup, then we investigate free-surface deformations induced by hydrodynamic turbulence. In a second stage an electromechanical shaker will generate gravity-capillary waves at the free surface. We aim to study reduction or amplification of surface waves and then measure energy exchange between hydrodynamic turbulence and wave turbulence. [Preview Abstract] |
Tuesday, November 25, 2014 2:23PM - 2:36PM |
R11.00007: Robust energy transfer mechanism via precession resonance in nonlinear turbulent wave systems Dan Lucas, Miguel Bustamante, Brenda Quinn The precise mechanisms by which energy is most efficiently transferred in a turbulent system remain an important open question for the fluid mechanics community. In this talk we present a newly discovered resonance which is found to drive transfers across the spectrum of Fourier modes in a nonlinear wave system. Quadratic nonlinearity results in modes interacting in triads and, by considering the ``truly dynamical degrees of freedom'' (amplitudes and triad phases) and the precessional frequencies of the triads, we show transfers are maximal when the precession resonates with the nonlinear temporal frequencies. This can lead to a collective state of synchronised triads with intense cascades at \emph{intermediate} nonlinearity; we find greatest transfer \emph{between} the traditional weak and strong turbulence regimes and discover that this new mechanism is dominant here. We present the effect in a hierarchy of models including a full DNS of the Charney-Hasegawa-Mima equation and confirm analytical predictions. [Preview Abstract] |
Tuesday, November 25, 2014 2:36PM - 2:49PM |
R11.00008: Airflow separation events above surface waves Fabrice Veron, Marc Buckley Airflow dynamics above waves strongly influence exchanges of heat, momentum and mass between the Ocean and the Atmosphere. We present experimental results on the details of the airflow above surface gravity waves for a several wind speeds, wave ages and slopes. The bulk of the results presented were obtained from a series of laboratory experiments that took place at the University of Delaware's Air-sea interaction facility. Airflow properties within and above the viscous sublayer were obtained using PIV, and wave profiles and spectra were measured by laser-induced fluorescence. We observe direct evidence of intermittent separation of the viscous sublayer past the crest of the wind waves. Despite the intermittent aspect of this phenomenon, ensemble averages of the wave phase-locked velocity products suggests the airflow separation yield significant flux of vorticity away from the surface thereby generating intense mixing and momentum transport within the airflow. These events, in turn, may affect wave growth and the air-water momentum balance. Our results hold for wind speeds that would normally be considered low to moderate. Implications for models of air-sea momentum flux will be discussed. [Preview Abstract] |
Tuesday, November 25, 2014 2:49PM - 3:02PM |
R11.00009: Transverse instability and viscous dissipation of forced 3-D gravity-capillary solitary waves on deep water Yeunwoo Cho The shedding phenomena of 3-D viscous gravity-capillary solitary waves generated by a moving air-forcing on the surface of deep water are investigated. Near the resonance where the forcing speed is close to 23 cm/s, two kinds of shedding modes are possible; Anti-symmetric and symmetric modes. A relevant theoretical model equation is numerically solved for the identification of shedding of solitary waves, and is analytically studied in terms of their linear stability to transverse perturbations. Furthermore, by tracing trajectories of shed solitary waves, the decay rate of a 3-D solitary wave due to viscous dissipation is estimated. [Preview Abstract] |
Tuesday, November 25, 2014 3:02PM - 3:15PM |
R11.00010: Experimental investigation of three-wave interactions of capillary surface-waves Michael Berhanu, Annette Cazaubiel, Luc Deike, Timothee Jamin, Eric Falcon We report experiments studying the non-linear interaction between two crossing wave-trains of gravity-capillary surface waves generated in a closed laboratory tank. Using a capacitive wave gauge and Diffusive Light Photography method, we detect a third wave of smaller amplitude whose frequency and wavenumber are in agreement with the weakly non-linear triadic resonance interaction mechanism. By performing experiments in stationary and transient regimes and taking into account the viscous dissipation, we estimate directly the growth rate of the resonant mode in comparison with theory. These results confirm at least qualitatively and extend earlier experimental results obtained only for unidirectional wave train. Finally we discuss relevance of three-wave interaction mechanisms in recent experiment studying capillary wave turbulence. [Preview Abstract] |
Tuesday, November 25, 2014 3:15PM - 3:28PM |
R11.00011: Rogue Wave Modes for the Long Wave-Short Wave Resonance and the Derivative Nonlinear Schr\"{o}dinger Models Hiu Ning Chan, Kwok Wing Chow, David Jacob Kedziora, Roger Hamilton James Grimshaw, Edwin Ding Rogue waves are unexpectedly large displacements of the water surface and will obviously pose threat to maritime activities. Recently, the formation of rogue waves is correlated with the onset of modulation instabilities of plane waves of the system. The long wave-short wave resonance and the derivative nonlinear Schr\"{o}dinger models are considered. They are relevant in a two-layer fluid and a fourth order perturbation expansion of free surface waves respectively. Analytical solutions of rogue wave modes for the two models are derived by the Hirota bilinear method. Properties and amplitudes of these rogue wave modes are investigated. Conditions for modulation instability of the plane waves are shown to be precisely the requirements for the occurrence of rogue waves. In contrast with the nonlinear Schr\"{o}dinger equation, rogue wave modes for the derivative nonlinear Schr\"{o}dinger model exist even if the dispersion and cubic nonlinearity are of the opposite signs, provided that a sufficiently strong self-steepening nonlinearity is present. Extensions to the coupled case (multiple waveguides) will be discussed. [Preview Abstract] |
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