Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session P01: Waves and Free Surface Flows: Turbulence |
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Chair: James H. Duncan, University of Maryland Room: 2A |
Monday, November 25, 2019 5:16PM - 5:29PM |
P01.00001: Discrete Wave Turbulence on Rational and Irrational Tori Alexander Hrabski, Yulin Pan We consider the long-term dynamics of nonlinear dispersive waves in a finite domain. This configuration arises both naturally (e.g., surface waves in a finite tank) and computationally (e.g., when periodic boundary conditions are used to approximate an infinite system). While the finite domain effect on the formation of power-law wave spectra has been studied in the framework of discrete wave turbulence, the effect of the aspect ratio of the domain has remained unexplored. In this work, we study the long-term evolution of the two-dimensional MMT (Majda, Mclaughlin, Tabak) equation on both rational and irrational tori (mapped from two-dimensional planes with rational and irrational aspect ratios). It is shown that the dynamics (e.g. power-law spectra) of the two systems are remarkably different, especially at lower nonlinearity levels. The results are explained in the context of discrete nonlinear resonances, in particular by the survival of exact resonances on rational/irrational tori. We conclude by outlining the implications of these findings for other physical wave contexts. [Preview Abstract] |
Monday, November 25, 2019 5:29PM - 5:42PM |
P01.00002: Experiment realization of a soliton gas in shallow water Nicolas Mordant, Ivan Redor, Eric Barthelemy, Herve Michallet, Miguel Onorato Solitons are nonlinear waves that behave as quasi particles and undergo elastic collisions. Solitons are typical solutions of integrable equations including the famous Korteweg-de Vries equation for shallow water propagation. Here we focus on the case of integrable turbulence (or soliton gas) which is a random state made of a large ensemble of nonlinear waves. Due to the integrable nature of the evolution, no classical thermalization can occur and the question of the large time statistical properties of such state remains open. Here we focus on the case of shallow water and we present a laboratory realization of such a soliton gas. We use a 34m-long flume with a water depth of 12 cm. A large number of solitons can be obtained by taking advantage of the decomposition of an initial sine wave forced by a piston wave maker into trains of solitons. Additionally we have a reflective end to the flume so that to keep solitons in the flume for a long time. Although our system is dissipative as viscosity cannot be avoided, the short time propagation is consistent with integrable behavior and we observe a soliton gas which statistical properties are consistent with numerical simulations of conservative waves. [Preview Abstract] |
Monday, November 25, 2019 5:42PM - 5:55PM |
P01.00003: Hypergravity Wave Turbulence Eric Falcon, Annette Cazaubiel, Sebastien Mawet, Alexis Darras, Galien Grosjean, Jack J.W.A Van Loon, Stephane Dorbolo Wave turbulence occurs in various domains of physics (plasma physics, elastic waves, or fluid mechanics) but is far to be completely understood, notably for ocean surface waves. By using a large-diameter centrifuge (LDC), we are able to tune the gravity field up to 20 times the Earth acceleration. This new technique then allows us to report the first observation of gravity wave turbulence on the surface of a fluid in hyper-gravity environment. This is also a unique solution to significantly expand the inertial range of gravity wave turbulence in the laboratory. Wave turbulence properties are then reported as function of the gravity level, and we show that the usual energy transfer by nonlinear wave interactions are modified by large-scale container modes. [Preview Abstract] |
Monday, November 25, 2019 5:55PM - 6:08PM |
P01.00004: Experimental study of 3D internal gravity wave turbulence in the Coriolis facility Clement Savaro, Antoine Campagne, Thomas Valran, Samuel Viboud, Joel Sommeria, Nicolas Mordant In geophysical flows energy can be transported by internal gravity waves that contribute also to a large amount of energy dissipation and mixing. When continuously excited by external forces like wind, currents or tides and coupled by nonlinearity they can develop a state of wave turbulence. The weak turbulence theory (WTT) can predict the stationary spectra of many waves systems but it application to internal waves remains questionable \footnote{Y V Lvov et al., \textbf{J. Phys. Oceanogr.} 42(5):669, 2012}. We build an experiment to study internal waves turbulence in 3D. Inside the 13 m-diameter tank of the Coriolis facility, four 6~m-long wall are set to form a 6X6X1~m$^3$ square box. The box is filled with a stable linear stratification of salt water. This stratification allows internal waves to be generated from two adjacent walls that can oscillate independently around their horizontal axis at a frequency slightly modulated in a narrow band. We performed time and space resolved PIV measurements. Spatio-temporal analysis of the PIV measurements confirm that internal waves are generated by non-linearity even far from the forcing frequencies. Discrete modes due to finite size effect are observed as well as a continuum of modes. [Preview Abstract] |
Monday, November 25, 2019 6:08PM - 6:21PM |
P01.00005: Wave-resolved direct numerical simulation of the generation of Langmuir circulations under progressive waves. Meng Li, Di Yang In open-water environment, the interaction of progressive surface waves with the shear turbulence generated by wind-induced surface shear stress causes the generation of Langmuir circulations -- a flow phenomenon frequently occurring in oceans and large lakes. In this generation process, the accumulated effect of the periodic distortion of the vortical structures in the shear-driven turbulence by the wave strain-rate field plays an essential role for the incipient generation of the Langmuir circulations. In this study, the detailed generation process of the Langmuir circulations by the wave-turbulence interaction is simulated using a wave phase resolved direct numerical simulation (DNS) approach. The complex flow motions are decomposed into an irrotational wave velocity field and a rotational turbulence field. With the wave field being imposed, the DNS solves the evolution of the turbulence field under wave distortion. This DNS model is found to successfully capture the incipient generation and evolution of the Langmuir circulations caused by wave-turbulence interaction. In this talk, both the time evolution of the instantaneous flow field obtained from the DNS and the statistical analysis results will be presented. [Preview Abstract] |
Monday, November 25, 2019 6:21PM - 6:34PM |
P01.00006: Surface Waves Enhance Particle Dispersion Mohammad Farazmand, Themis Sapsis How quickly does a point source of pollution spread in a fluid flow? Taylor's single-particle dispersion theory predicts that, in homogeneous isotropic turbulence, the tracer variance $\langle |X(t)|^2\rangle$ grows quadratically for short times ($\langle |X(t)|^2\rangle\sim t^2$) and linearly for large times ($\langle |X(t)|^2\rangle\sim t$). We show that these predictions break down for tracers dispersed on the free surface of a gravity wave. Using an exact nonlinear model to advect the tracer particles, we show that the nonlinear effects significantly enhance the dispersion. In particular, the tracer variance grows as $\langle |X(t)|^2\rangle\sim t^4$ for times $t$ less than one wave period. In the asymptotic limit, as $t$ increases beyond one wave period, the variance grows quadratically with time, i.e., $\langle |X(t)|^2\rangle\sim t^2$. We show that this super-diffusive behavior is a result of the long-term correlation of the Lagrangian velocities of fluid parcels on the free surface. [Preview Abstract] |
Monday, November 25, 2019 6:34PM - 6:47PM |
P01.00007: Large-eddy simulation of oil droplet aerosol transport in wind over waves. Di Yang, Meng Li, Yajat Pandya, Giacomo Valerio Iungo In this study, large-eddy simulations (LES) are performed to study the transport of aerosolized small oil droplets in wind over surface waves. The LES model consists of a wind turbulence solver and an Eulerian scalar transport solver. The wind LES solver uses a boundary fitted computational grid system that follows the instantaneous sea-surface waves to capture the turbulent flow structures and transport phenomena near the sea surface, and a hybrid pseudo-spectral and finite-difference method for spatial discretization. The aerosol transport is modeled using an Eulerian approach, in which an advection-diffusion equation for the oil droplet concentration field is solved using the finite-volume method with a combination of upwinding scheme and central difference scheme. Using this LES model, a set of simulations with various oil droplet sizes and sea-surface conditions are performed to investigate their effects on the vertical and lateral transports of oil aerosols in the marine atmospheric boundary layer. [Preview Abstract] |
Monday, November 25, 2019 6:47PM - 7:00PM |
P01.00008: Froude number effects on free surface turbulence in open channel flow Yujia Di, Bingqing Deng, Anqing Xuan, Ye Li, Lian Shen Direct numerical simulations of free surface turbulent flows in open channel at different Froude numbers have been conducted to study the surface deformation and the turbulence below. The deformation of the free surface is captured using a boundary-fitted grid and fully nonlinear free-surface boundary conditions. By studying the frequency-wavenumber spectrum of surface elevation, we find that the advection of the mean current alone contributes to the surface deformation at low Fr, while the contribution of the surface wave becomes more important as Fr increases. It is also found that in the bulk flow region, more energy of the streamwise velocity component is distributed at large length scales as Fr increases, indicating that the Fr number effect can also reach into the bulk region. The underlying mechanism of the modified bulk flows at high Fr numbers is further analyzed using the TKE budget spectrum. [Preview Abstract] |
Monday, November 25, 2019 7:00PM - 7:13PM |
P01.00009: Scale effects for air entrainment in quasi-steady breaking waves Kelli Hendrickson, Dick Yue Quasi-steady breaking waves are prominent and highly observable features in civil, environmental, ocean and naval engineering applications with direct impact on turbulent dissipation and air-sea interaction. We use high-resolution 3D direct numerical simulation of quasi-steady breaking waves to study the air entrainment characteristics as a function of resolvable features within the wave. The numerical method utilizes conservative Volume of Fluid (cVOF) to capture the interface on a Cartesian grid. A submerged body generates the quasi-steady breaking wave. Our particular interest lies in developing parameterizations and models that relate the entrainment due to quasi-steady wave breaking to underlying flow characteristics. For different Froude numbers $Fr$, we observe two flow regimes: a periodic-wave-breaking and a metastable regime. For the periodic-wave-breaking regime we show that the bubble-size distribution (above the capillary length scale) for each entrainment period achieves an expected slope of $r^{-\beta}$, $\beta$=10/3 and the mean volume of entrained air scales linearly with $Fr^2$. We also observe a direct correlation between strong underlying vertical vorticity flux events and surface entrainment. The behavior and scaling in the metastable regime is different and [Preview Abstract] |
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