Hurther D.,CNRS Laboratory of Geophysical and Industrial Flows |
Thorne P.D.,National Oceanography Center
Journal of Geophysical Research: Oceans | Year: 2011
The present study focuses on the fine-scale flow and sand transport processes above onshore migrating ripples below skewed surface gravity waves in the shoaling zone. A set of acoustic instruments was deployed in the shoaling region of the large-scale wave channel at Canal d'Investigacío i Experimatacío Marítima, Universitat Polticnica de Catalunya, Barcelona, Spain, in order to provide high-resolution velocity and sediment concentration profiles with an acoustic concentration and velocity profiler (ACVP). Measurements are analyzed relative to the positions of the measured nonmoving sand bed and the interface separating the suspension from the near-bed load layer. This interface is detected here by the application of a novel acoustic bed echo detection method. Furthermore, the use of the dual-frequency inversion proposed in the work of Hurther et al. (2011) allows for the calculation of the sediment concentration profile across both the suspension and near-bed load layers. The sand bed was covered by quasi-two-dimensional suborbital ripples migrating onshore. As proposed by O'Donoghue et al. (2006), the occurrence of quasi-two-dimensional ripples is attributed to the fine-size sand of D50 = 250 m used in the present study under full-scale forcing conditions. In order to determine the effect of shoaled wave skewness on the ripple vortex entrainment and sediment transport, the instantaneous and mean measurements of the flow, sediment concentration, and sediment flux along the ripple profile are discussed in terms of (1) the occurrence of ripple vortex entrainment on either side of the ripple crest; (2) the wave velocity phase lagging driven by the ripple vortex entrainment process and the turbulent bed friction effects in the wave boundary layer; (3) phase lagging between velocity and maximum concentration and sediment flux events; (4) the structure of bed friction and ripple-driven turbulence across the suspension and the near-bed load layers; and (5) the streaming components. The results on these aspects strongly support that the wave velocity skewness effect under shoaling waves is fairly similar to the one obtained in skewed oscillatory water tunnel flows. Furthermore, it is found that the onshore-oriented net bed load sediment transport is at the origin of the onshore ripple migration. This flux is roughly twice as much as the opposite offshore-oriented net suspension flux dominated by the ripple vortex entrainment processes. Copyright 2011 by the American Geophysical Union.
Chassagneux F.X.,CNRS Laboratory of Geophysical and Industrial Flows |
Hurther D.,CNRS Laboratory of Geophysical and Industrial Flows
Journal of Geophysical Research: Oceans | Year: 2014
The present work investigates the structure of the near-bed flow below irregular surfzone breaking waves inducing light-weight sheet flow particle transport. The experiments are carried out in the LEGI flume under steady equilibrium conditions between the wave forcing and the underlying bed morphology. Synchronized ACVP and video images provide detailed information about the mean wave and current characteristics and the coupled flow regimes across the entire wave breaking region including the outer and the inner surfzones. An analysis of the impact of breaking eddies in the Wave Boundary Layer (WBL) is undertaken at the beginning of the inner surfzone. Subsequently, the intrawave variation of several contributions of the total shearing force per unit area and the net values of the Reynolds stress related to phase-averaged velocities are analyzed. It is found that -ρuw is the dominant term. The turbulent Reynolds stress, the low frequency, and the mean terms are at least 1 order of magnitude lower. Due to the irregular wave forcing, the net values are separated into the net wave-by-wave Reynolds stress and the wave Reynolds stress averaged over the entire irregular wave sequence. All these measured bed shear stress terms are then compared to estimations obtained with two different parameterized models in order to evaluate their prediction performances. The values of the model parameters are discussed in comparison to those found in the literature. Finally, the vertical profile of net Reynolds shear stress exhibits a nearly constant value across the sheet-flow layer. Key Points Data set of near-bed measurements in wave flume Flow and sediment transport properties across the wave breaking region Bed shear stress predictions © 2014. American Geophysical Union. All Rights Reserved.
Revil-Baudard T.,CNRS Laboratory of Geophysical and Industrial Flows |
Chauchat J.,CNRS Laboratory of Geophysical and Industrial Flows
Journal of Geophysical Research: Oceans | Year: 2013
A two-phase model having a m(I) rheology for the intergranular stresses and a mixing length approach for the turbulent stresses is proposed to describe the sheet flow regime of sediment transport. In the model, two layers are considered: a dilute suspension layer and a dense sediment bed layer. The concentration profile is obtained from the dilatancy law f(I) in the sediment bed layer and from a Rouse profile in the suspension layer. The comparison of velocity profile, concentration profile, and macroscopic parameters (sediment transport rate, thickness, and roughness) with experimental data shows a good agreement. These comparisons demonstrate that the dense granular rheology is relevant to describe intense bed-load transport in turbulent regime (sheet flow). The transition from the dense static bed to the dilute suspension is well described by the present model. Also, the different regimes of the dense granular rheology seems to be able to capture the transition between collision-dominant and turbulent-fluctuations-dominant sheet flows, depending on the particle's characteristics. © 2012 American Geophysical Union. All Rights Reserved.
Thorne P.D.,National Oceanography Center |
Hurther D.,CNRS Laboratory of Geophysical and Industrial Flows
Continental Shelf Research | Year: 2014
For over two decades, coastal marine scientists studying boundary layer sediment transport processes have been using, and developing, the application of sound for high temporal-spatial resolution measurements of suspended particle size and concentration profiles. To extract the suspended sediment parameters from the acoustic data requires an understanding of the interaction of sound with a suspension of sediments and an inversion methodology. This understanding is distributed around journals in a number of scientific fields and there is no single article that succinctly draws together the different components. In the present work the aim is to provide an overview on the acoustic approach to measuring suspended sediment parameters and assess its application in the study of non-cohesive inorganic suspended sediment transport processes. © 2013.
Goncalves E.,CNRS Laboratory of Geophysical and Industrial Flows
Computers and Fluids | Year: 2013
A compressible, multiphase, one-fluid inviscid solver has been developed to investigate the behavior of various cavitation models. A new source term for the mass transfer between phases is proposed. A range of models from three to five equations is compared. Numerical simulations are performed on rarefaction problems and compared with reference solutions. © 2012 Elsevier Ltd.
Goncalves E.,CNRS Laboratory of Geophysical and Industrial Flows
International Journal of Heat and Mass Transfer | Year: 2014
A compressible, two-phase, one-fluid solver has been developed to investigate the behaviour of cavitation models including thermodynamic effects. The code is composed by three conservation laws for mixture variables (mass, momentum and total energy) and a supplementary transport equation for the void ratio. Two formulations for the mass transfer between phases are studied. Numerical simulations are firstly performed on rarefaction cavitating problems in which the working fluid is hot water and freon R-114. A realistic turbulent Venturi case with freon R-114 is performed and comparisons are done between 3- and 4-equation models. A warming effect is highlighted downstream the cavitation pocket in the region of pressure recuperation. © 2014 Elsevier Ltd. All rights reserved.
Goncalves E.,CNRS Laboratory of Geophysical and Industrial Flows |
Charriere B.,CNRS Laboratory of Geophysical and Industrial Flows
International Journal of Multiphase Flow | Year: 2014
In a recent study, an original formulation for the mass transfer between phases has been proposed to study one-dimensional inviscid cavitating tube problems. This mass transfer term appears explicitly as a source term of a void ratio transport-equation model in the framework of the homogenous mixture approach. Based on this generic form, a two-dimensional preconditioned Navier-Stokes one-fluid solver is developed to perform realistic cavitating flows. Numerical results are given for various inviscid cases (underwater explosion, bubble collapse) and unsteady sheet cavitation developing along Venturi geometries at high Reynolds number. Comparisons with experimental data (concerning void ratio and velocity profiles, pressure fluctuations) and with a 3-equation model are presented. © 2013 Elsevier Ltd.
Goncalvs E.,CNRS Laboratory of Geophysical and Industrial Flows
European Journal of Mechanics, B/Fluids | Year: 2011
The simulation of cavitating flows is a challenging problem both in terms of modelling the physics and developing robust numerical methodologies. Such flows are characterized by important variations of the local Mach number, compressibility effects on turbulence and involve thermodynamic phase transition. To simulate these flows by applying homogeneous models and Reynolds averaged codes, the turbulence modelling plays a major role in the capture of unsteady behaviours. This paper presents a one-fluid compressible Reynolds-Averaged NavierStokes (RANS) solver with a simple equation of state (EOS) for the mixture. A special focus is devoted to the turbulence model influence. Unsteady numerical results are given for Venturi geometries and comparisons are made with experimental data. © 2010 Elsevier Masson SAS. All rights reserved.
Chauchat J.,CNRS Laboratory of Geophysical and Industrial Flows |
Medale M.,Aix - Marseille University
Journal of Computational Physics | Year: 2014
This paper presents a three-dimensional implementation of the so-called μ(I) rheology to accurately and efficiently compute steady-state dense granular flows. The tricky pressure dependent visco-plastic behaviour within an incompressible flow solver has been overcome using a regularisation technique along with a complete derivation of the incremental formulation associated with the Newton-Raphson algorithm. The computational accuracy and efficiency of the proposed numerical model have been assessed on two representative problems that have an analytical solution. Then, two application examples dealing with actual lab experiments have also been considered: the first one concerns a granular flow on a heap and the second one deals with the granular flow around a cylinder. In both configurations the obtained computational results are in good agreement with available experimental data. © 2013 Elsevier Inc.
Van Haren H.,Netherlands Institute for Sea Research |
Gostiaux L.,CNRS Laboratory of Geophysical and Industrial Flows
Geophysical Research Letters | Year: 2010
Detailed overturning is observed between 0.5 and 50 m above the sloping side of Great Meteor Seamount, Canary Basin, using 100 moored temperature sensors, 1 mK accurate, sampling at 1-Hz. While previously reported frontal bores of 40-m amplitude can form with vigorous near-bottom motions and sediment resuspension at the beginning of the upslope phase of large, e.g., tidal, carrier waves, the downslope phase presented here is more " permanently" turbulent away from the bottom. This turbulence is inferred from high-resolution temperature space-time series, which reveal ubiquitous "finger-like" structures. It occurs during the clear-water tidal phase, with low amounts of acoustic scatterers. The high-frequency finger-like motions α> N, N the buoyancy frequency, are observed simultaneously with local mode-2 near-N inertio-gravity waves and overall shear S ≈ N. They show large temperature variations, 5-10 m vertical amplitudes and occasionally develop Kelvin-Helmholtz billows. The typical (Eulerian) period of these firstly observed deep-ocean billows amounts 50 ± 10 s. Copyright © 2010 by the American Geophysical Union.