Pierre Lubin - Academia.edu (original) (raw)
Papers by Pierre Lubin
Great improvements have been brought to the knowledge of the hydrodynamics and the general proces... more Great improvements have been brought to the knowledge of the hydrodynamics and the general processes occurring in the surf zone, widely affected by the breaking of the waves. Nevertheless, the turbulent flow structure is still very complicated to investigate. The description of the hydrodynamics in the surf zone is then a field of research requiring efforts and improvements. The rapid advances of the experimental techniques and the recent progresses in applied mathematics and computers architectures offer the possibility to overtake some limitations. On the basis of the published experimental [1-2] and numerical [3] works, the hydrodynamics of regular waves shoaling and breaking over a sloping beach is presented. The breaking processes including shoaling, overturning, splash-up and air entrainment, will be presented and discussed. The turbulent flow structures generation will be carefully described. The experiments were conducted in the EGIM wave tank, which is 17 m long and 0.65 m ...
We present a novel robust, accurate and efficient hybrid strategy by coupling WENO5 and HOUC5 sch... more We present a novel robust, accurate and efficient hybrid strategy by coupling WENO5 and HOUC5 schemes for the spatial discretization of the advection equation in a level set framework. This one is based on two main observations. First, from its definition, the level set function is globally a smooth function in the whole domain except where kink points are detected. And secondly, for smooth regions, the 5 th order Weighted Essentially Non-Oscillatory (WENO5) scheme reduces to compute a 5 th order High-Order Upstream Central (HOUC5) scheme, which has a lower computational cost. The introduced hybrid scheme HWH5, for hybrid WENO5 scheme HOUC5 scheme, coupled the robustness of a WENO5 scheme for all regions where the spatial discretization of the advection equation is subject to large error, i.e. where a kink is detected, with the efficiency of a HOUC5 scheme for smooth regions. The efficiency and robustness of this approach are demonstrated on a variety of benchmarks, where the hybrid approach presents equivalent results to the WENO5 scheme for a computational cost lowered with a factor up to 2. Alongside, we also present that the sole use of the efficient HOUC5 scheme for the spatial discretization of the advection equation presents anti-diffusive behaviours on the volume conservation and may lead to the introduction of noticeable perturbations of the interface which can be dreadful overtime on the overall dynamic. Conversely, WENO5 presents diffusive results in irregular regions. Hence, the adequate coupling of these two schemes in HWH5 allows obtaining a method as robust as WENO5 for a valuable lowered computational cost.
Indeed, some striking features can be highlighted in two-dimensional simulations, such as large v... more Indeed, some striking features can be highlighted in two-dimensional simulations, such as large velocity fluctuations and flow recirculation structures. Using Large Eddy Simulation method, the numerical results emphasised the complicated turbulent structures and their unsteadiness under a tidal bore.
Australasian Fluid Mechanics Conference (AFMC), 2020
Modelling wave breaking at relatively large Reynolds numbers remain a challenge for both numerica... more Modelling wave breaking at relatively large Reynolds numbers remain a challenge for both numerical modeler and experimentalists, due to the complexity between the two-phase air-water interactions, highly turbulent unpredictable hydrodynamics, and a lack of solid validation datasets. This study presents a recent attempt to simulate a three-dimensional breaking wave propagating in a long rectangular channel, at relatively high Froude (Fr1 = 1.5) and Reynolds number (Re ~ 10 5). The numerical model used a Large Eddy Simulation coupled with a Volume of Fluid method to track the interface between air and water. The turbulence was injected using a Synthetic Eddy Method. The numerical results were validated against experimental datasets, which were collected under the exact same initial and boundary flow conditions in a controlled laboratory environment. Systematic validations showed: (1) the generation process of a breaking shock wave is a complicated process which was not accurately modelled by simple boundary conditions; (2) the propagation process following an unrealistic generation could lead to false prediction in free-surface profile, velocity field, and turbulent mixing; (3) the bubble motions (collision, agglomeration and break-up) during surge propagation were poorly predicted, comparing to observations of real-fluid flow; (4) the de-aeration process was grossly underestimated in the numerical result.
When simulating two-phase flows, it is important to evaluate the general accuracy and the validit... more When simulating two-phase flows, it is important to evaluate the general accuracy and the validity of the numerical methods and numerical schemes used and the conservation laws of mass and energy in the computing domain. In particular, it is important to check that the behavior of the interface between two media is well taken into account, considering surface tension and viscous effects. As a matter of fact, capillary waves are similar to gravity waves but, firstly, they involve smaller scales, both in length and time. Secondly, They require a more difficult computation, because surface tension forces are based on the interface curvature, which needs to be accurately described. Thus, the results provided for pure capillary waves are considered, as initial conditions to simulate their propagations in constant depths over horizontal beds. The precision of the simulation is checked by comparing the free-surface shapes to theoretical values, including the predicted decay rate due to vis...
A tidal bore may form during spring tide conditions when the tidal range exceeds 4 to 6 m in a na... more A tidal bore may form during spring tide conditions when the tidal range exceeds 4 to 6 m in a natural estuary with a funnel shaped river mouth and shallow initial water level. The propagation of tidal bores is a highly unsteady turbulent process associated with intensive sediment scouring and mixing. To date few physical and numerical studies documented the unsteady turbulent process of tidal bore propagation. Recent numerical CFD models lacked careful experimental validations. The present study aims to provide new results on CFD numerical modelling of tidal bore propagation with a wide range of Froude numbers (1.2 to 2.1) and systematic experimental validations. The model solved the incompressible Navier-Stokes equations in its twophase flow forms using Large Eddy Simulation (LES). Both 2D and 3D simulations were conducted; the inlet turbulence of the 3D models was simulated by a Synthetic Eddy Method (SEM). The physical experiments were based upon an ensemble-average technique, w...
A positive surge or bore is an unsteady rapidly-varied open channel flow characterised by a rise ... more A positive surge or bore is an unsteady rapidly-varied open channel flow characterised by a rise in water surface elevation. After formation, the bore is traditionally analysed as a hydraulic jump in translation and its leading edge is characterised by a breaking roller for Fr1 > 1.3-1.5. The roller is a key flow feature characterised by intense turbulence and air bubble entrainment. Herein detailed air-water flow measurements were conducted in breaking bores propagating in a large-size channel. The data showed a relatively steep roller, with a short and dynamic bubbly flow region. The results were used to validate a Computational Fluid Dynamics (CFD) model of breaking bores. The instantaneous void fraction and bubble distribution data showed systematically a lesser aeration region in the physical model, compared to the numerical data. The differences may be linked to some limitation of the CFD modelling.
Journal of Computational Physics, 2022
Fuel and Energy Abstracts, 2005
Fuel science and technology (fundamental science, analysis, instrumentation) experimental data fo... more Fuel science and technology (fundamental science, analysis, instrumentation) experimental data for water show smaller values than the theoretical ones. The authors consider the differences are due tO the existence of non-condensable gases in the experimental system. A non-equilibrium MD study is also included in this paper for a discussion on the inverted temperature profiles. 05/02808 A new approach using artificial neural networks for determination of the thermodynamic properties of fluid couples
International Journal of Sediment Research, 2018
Tidal bores may appear in some estuaries when the tides quickly reach a high level. This phenomen... more Tidal bores may appear in some estuaries when the tides quickly reach a high level. This phenomenon is rare but has a strong impact during its short duration: i.e. the river bed is significantly eroded and sediments are then transported. In this paper, the trajectories of suspended particles induced by this flow are numerically studied. Four undular bores with Froude numbers between 1.1 and 1.2 are studied. Despite similar Froude numbers, various initial flow conditions were selected to produce or not an inversion of the flow direction during the bore passage. The particle trajectories associated with each distinct flow configuration are presented and analyzed. These trajectories, estimated by solving the Maxey-Riley equation, appear to be very different even though the Froude numbers of flows are similar. These observations are important because the Froude number is often used to characterize a tidal bore as it describes well the free surface, however, it cannot describe the sediment transport. Finally, Chen's model of wave-current interactions is adapted to fit the cases studied and is applied to the four bores simulated. The results highlight that this latter model can reproduce the observed trajectories and dissociate their different components. From this model, it is shown that the inertial and Basset history effects can be neglected compared to the gravity and flow entrainment effects due to the viscous drag when one wants to determine the long-term trajectories of suspended particles.
Turbulence, 2006
ABSTRACT This paper is a second step in the long way towards the use of LES-like simulations to t... more ABSTRACT This paper is a second step in the long way towards the use of LES-like simulations to tackle with convective boiling flows. Our previous contributions have started to clarify some aspects of the isothermal momentum transfer through an interface and explain some of the couplings that exist between the kinetic energy and the interfacial energy; the present contribution gives our first results on the internal energy transfer through an interface in the frame of a simple situation where phase-change does not exist. A set of Large Eddy Simulation (LES) filtered two-phase flow governing equations is proposed. Explicit filtering of Direct Numerical Simulations (DNS) is employed to evaluate the order of magnitude of the subgrid contributions. Simple structural models are proposed for the two dominant contributions and compared successfully with a priori evaluations performed on the DNS.
Multiphase Science and Technology, 2004
The 26 December 2004 and 10 March 2011 tsunami disasters highlighted the rapid advance of the tsu... more The 26 December 2004 and 10 March 2011 tsunami disasters highlighted the rapid advance of the tsunami waters following rivers and canals causing massive damage deep inland. The leading edge of the tsunami formed a series of waves propagating upriver. This phenomenon is called 'shio-tsunami' (bore), 'kaisho' (tsunami-induced bore) or simply 'tsunami' (tidal wave) in Japan. After breaking, a tsunami wave propagating in shallow-waters is led by a bore. In these rivers and shallow-water bays, the propagation of the bores is associated with strong mixing and massive sedimentary processes upriver. This contribution reviews a number of tsunami-induced bore disasters, before studying the tsunami propagation upriver. The aim of the contribution is to provide compelling evidences on the turbulent mixing and sediment processes induced by tsunami bores based upon some recent field observations as well as physical and numerical studies of tidal bores. It is shown that the propagation of the bore front modifies drastically the water column properties and the tsunami waters behind the front may carry a large amount of sediments, explaining some of the sedimentological and morphological changes observed after some recent disasters.
Multiphase Science and Technology, 2004
Journal of Fluids and Structures, 2013
Abstract Air entrainment upon impact of a jet of liquid is a phenomenon present in wide variety o... more Abstract Air entrainment upon impact of a jet of liquid is a phenomenon present in wide variety of applications. We performed a series of two-dimensional simulations consisting in three different conditions of jet impingement and compared the results to experimental data. This study was first dedicated to the establishment of the numerical configuration and the setting of the injection parameters of the jet. We studied the dynamics of air entrainment by the jets impacting on the surface of the water in a tank, from the creation of the aerated cavities to the motion of the bubble plumes resulting from their deterioration of the cavities. The results concerned time-dependent and transient phenomena. To validate the simulations, we made several comparisons with experimental data, considering three angles of jet impact. Finally, we compared two numerical models for the free-surface description, using the most prevalent method in the literature and an original free-surface tracking method recently developed in our numerical tool. We showed that the formation of air cavities was similar for each condition and each numerical model, in agreement with the experimental results. Moreover, it was observed that the air entrainment had a different behavior depending on the conditions of jet impact.
Estuarine, Coastal and Shelf Science, 2011
The study details new sediment concentration measurements associated with some turbulence charact... more The study details new sediment concentration measurements associated with some turbulence characterisation conducted at high frequency in the undular tidal bore of the Garonne River (France). Acoustic Doppler velocimetry was used, and the suspended sediment concentration was deduced from the acoustic backscatter intensity. The field data set demonstrated some unique flow features of the tidal bore including some large and rapid turbulent velocity fluctuations during and after the bore passage. Some unusually high suspended sediment concentration was observed about 100 s after the tidal bore front lasting for more than 10 minutes. It is thought that the tidal bore passage scoured the bed and convected upwards the bed material, reaching the free-surface after the bore passage. Behind the tidal bore, the net sediment flux magnitude was 30 times larger than the ebb tide net flux and directed upstream. A striking feature of the data set was the intense mixing and suspended sediment motion during the tidal bore and following flood tide. This feature has been rarely documented.
Advanced Numerical Modelling of Wave Structure Interactions, 2021
Great improvements have been brought to the knowledge of the hydrodynamics and the general proces... more Great improvements have been brought to the knowledge of the hydrodynamics and the general processes occurring in the surf zone, widely affected by the breaking of the waves. Nevertheless, the turbulent flow structure is still very complicated to investigate. The description of the hydrodynamics in the surf zone is then a field of research requiring efforts and improvements. The rapid advances of the experimental techniques and the recent progresses in applied mathematics and computers architectures offer the possibility to overtake some limitations. On the basis of the published experimental [1-2] and numerical [3] works, the hydrodynamics of regular waves shoaling and breaking over a sloping beach is presented. The breaking processes including shoaling, overturning, splash-up and air entrainment, will be presented and discussed. The turbulent flow structures generation will be carefully described. The experiments were conducted in the EGIM wave tank, which is 17 m long and 0.65 m ...
We present a novel robust, accurate and efficient hybrid strategy by coupling WENO5 and HOUC5 sch... more We present a novel robust, accurate and efficient hybrid strategy by coupling WENO5 and HOUC5 schemes for the spatial discretization of the advection equation in a level set framework. This one is based on two main observations. First, from its definition, the level set function is globally a smooth function in the whole domain except where kink points are detected. And secondly, for smooth regions, the 5 th order Weighted Essentially Non-Oscillatory (WENO5) scheme reduces to compute a 5 th order High-Order Upstream Central (HOUC5) scheme, which has a lower computational cost. The introduced hybrid scheme HWH5, for hybrid WENO5 scheme HOUC5 scheme, coupled the robustness of a WENO5 scheme for all regions where the spatial discretization of the advection equation is subject to large error, i.e. where a kink is detected, with the efficiency of a HOUC5 scheme for smooth regions. The efficiency and robustness of this approach are demonstrated on a variety of benchmarks, where the hybrid approach presents equivalent results to the WENO5 scheme for a computational cost lowered with a factor up to 2. Alongside, we also present that the sole use of the efficient HOUC5 scheme for the spatial discretization of the advection equation presents anti-diffusive behaviours on the volume conservation and may lead to the introduction of noticeable perturbations of the interface which can be dreadful overtime on the overall dynamic. Conversely, WENO5 presents diffusive results in irregular regions. Hence, the adequate coupling of these two schemes in HWH5 allows obtaining a method as robust as WENO5 for a valuable lowered computational cost.
Indeed, some striking features can be highlighted in two-dimensional simulations, such as large v... more Indeed, some striking features can be highlighted in two-dimensional simulations, such as large velocity fluctuations and flow recirculation structures. Using Large Eddy Simulation method, the numerical results emphasised the complicated turbulent structures and their unsteadiness under a tidal bore.
Australasian Fluid Mechanics Conference (AFMC), 2020
Modelling wave breaking at relatively large Reynolds numbers remain a challenge for both numerica... more Modelling wave breaking at relatively large Reynolds numbers remain a challenge for both numerical modeler and experimentalists, due to the complexity between the two-phase air-water interactions, highly turbulent unpredictable hydrodynamics, and a lack of solid validation datasets. This study presents a recent attempt to simulate a three-dimensional breaking wave propagating in a long rectangular channel, at relatively high Froude (Fr1 = 1.5) and Reynolds number (Re ~ 10 5). The numerical model used a Large Eddy Simulation coupled with a Volume of Fluid method to track the interface between air and water. The turbulence was injected using a Synthetic Eddy Method. The numerical results were validated against experimental datasets, which were collected under the exact same initial and boundary flow conditions in a controlled laboratory environment. Systematic validations showed: (1) the generation process of a breaking shock wave is a complicated process which was not accurately modelled by simple boundary conditions; (2) the propagation process following an unrealistic generation could lead to false prediction in free-surface profile, velocity field, and turbulent mixing; (3) the bubble motions (collision, agglomeration and break-up) during surge propagation were poorly predicted, comparing to observations of real-fluid flow; (4) the de-aeration process was grossly underestimated in the numerical result.
When simulating two-phase flows, it is important to evaluate the general accuracy and the validit... more When simulating two-phase flows, it is important to evaluate the general accuracy and the validity of the numerical methods and numerical schemes used and the conservation laws of mass and energy in the computing domain. In particular, it is important to check that the behavior of the interface between two media is well taken into account, considering surface tension and viscous effects. As a matter of fact, capillary waves are similar to gravity waves but, firstly, they involve smaller scales, both in length and time. Secondly, They require a more difficult computation, because surface tension forces are based on the interface curvature, which needs to be accurately described. Thus, the results provided for pure capillary waves are considered, as initial conditions to simulate their propagations in constant depths over horizontal beds. The precision of the simulation is checked by comparing the free-surface shapes to theoretical values, including the predicted decay rate due to vis...
A tidal bore may form during spring tide conditions when the tidal range exceeds 4 to 6 m in a na... more A tidal bore may form during spring tide conditions when the tidal range exceeds 4 to 6 m in a natural estuary with a funnel shaped river mouth and shallow initial water level. The propagation of tidal bores is a highly unsteady turbulent process associated with intensive sediment scouring and mixing. To date few physical and numerical studies documented the unsteady turbulent process of tidal bore propagation. Recent numerical CFD models lacked careful experimental validations. The present study aims to provide new results on CFD numerical modelling of tidal bore propagation with a wide range of Froude numbers (1.2 to 2.1) and systematic experimental validations. The model solved the incompressible Navier-Stokes equations in its twophase flow forms using Large Eddy Simulation (LES). Both 2D and 3D simulations were conducted; the inlet turbulence of the 3D models was simulated by a Synthetic Eddy Method (SEM). The physical experiments were based upon an ensemble-average technique, w...
A positive surge or bore is an unsteady rapidly-varied open channel flow characterised by a rise ... more A positive surge or bore is an unsteady rapidly-varied open channel flow characterised by a rise in water surface elevation. After formation, the bore is traditionally analysed as a hydraulic jump in translation and its leading edge is characterised by a breaking roller for Fr1 > 1.3-1.5. The roller is a key flow feature characterised by intense turbulence and air bubble entrainment. Herein detailed air-water flow measurements were conducted in breaking bores propagating in a large-size channel. The data showed a relatively steep roller, with a short and dynamic bubbly flow region. The results were used to validate a Computational Fluid Dynamics (CFD) model of breaking bores. The instantaneous void fraction and bubble distribution data showed systematically a lesser aeration region in the physical model, compared to the numerical data. The differences may be linked to some limitation of the CFD modelling.
Journal of Computational Physics, 2022
Fuel and Energy Abstracts, 2005
Fuel science and technology (fundamental science, analysis, instrumentation) experimental data fo... more Fuel science and technology (fundamental science, analysis, instrumentation) experimental data for water show smaller values than the theoretical ones. The authors consider the differences are due tO the existence of non-condensable gases in the experimental system. A non-equilibrium MD study is also included in this paper for a discussion on the inverted temperature profiles. 05/02808 A new approach using artificial neural networks for determination of the thermodynamic properties of fluid couples
International Journal of Sediment Research, 2018
Tidal bores may appear in some estuaries when the tides quickly reach a high level. This phenomen... more Tidal bores may appear in some estuaries when the tides quickly reach a high level. This phenomenon is rare but has a strong impact during its short duration: i.e. the river bed is significantly eroded and sediments are then transported. In this paper, the trajectories of suspended particles induced by this flow are numerically studied. Four undular bores with Froude numbers between 1.1 and 1.2 are studied. Despite similar Froude numbers, various initial flow conditions were selected to produce or not an inversion of the flow direction during the bore passage. The particle trajectories associated with each distinct flow configuration are presented and analyzed. These trajectories, estimated by solving the Maxey-Riley equation, appear to be very different even though the Froude numbers of flows are similar. These observations are important because the Froude number is often used to characterize a tidal bore as it describes well the free surface, however, it cannot describe the sediment transport. Finally, Chen's model of wave-current interactions is adapted to fit the cases studied and is applied to the four bores simulated. The results highlight that this latter model can reproduce the observed trajectories and dissociate their different components. From this model, it is shown that the inertial and Basset history effects can be neglected compared to the gravity and flow entrainment effects due to the viscous drag when one wants to determine the long-term trajectories of suspended particles.
Turbulence, 2006
ABSTRACT This paper is a second step in the long way towards the use of LES-like simulations to t... more ABSTRACT This paper is a second step in the long way towards the use of LES-like simulations to tackle with convective boiling flows. Our previous contributions have started to clarify some aspects of the isothermal momentum transfer through an interface and explain some of the couplings that exist between the kinetic energy and the interfacial energy; the present contribution gives our first results on the internal energy transfer through an interface in the frame of a simple situation where phase-change does not exist. A set of Large Eddy Simulation (LES) filtered two-phase flow governing equations is proposed. Explicit filtering of Direct Numerical Simulations (DNS) is employed to evaluate the order of magnitude of the subgrid contributions. Simple structural models are proposed for the two dominant contributions and compared successfully with a priori evaluations performed on the DNS.
Multiphase Science and Technology, 2004
The 26 December 2004 and 10 March 2011 tsunami disasters highlighted the rapid advance of the tsu... more The 26 December 2004 and 10 March 2011 tsunami disasters highlighted the rapid advance of the tsunami waters following rivers and canals causing massive damage deep inland. The leading edge of the tsunami formed a series of waves propagating upriver. This phenomenon is called 'shio-tsunami' (bore), 'kaisho' (tsunami-induced bore) or simply 'tsunami' (tidal wave) in Japan. After breaking, a tsunami wave propagating in shallow-waters is led by a bore. In these rivers and shallow-water bays, the propagation of the bores is associated with strong mixing and massive sedimentary processes upriver. This contribution reviews a number of tsunami-induced bore disasters, before studying the tsunami propagation upriver. The aim of the contribution is to provide compelling evidences on the turbulent mixing and sediment processes induced by tsunami bores based upon some recent field observations as well as physical and numerical studies of tidal bores. It is shown that the propagation of the bore front modifies drastically the water column properties and the tsunami waters behind the front may carry a large amount of sediments, explaining some of the sedimentological and morphological changes observed after some recent disasters.
Multiphase Science and Technology, 2004
Journal of Fluids and Structures, 2013
Abstract Air entrainment upon impact of a jet of liquid is a phenomenon present in wide variety o... more Abstract Air entrainment upon impact of a jet of liquid is a phenomenon present in wide variety of applications. We performed a series of two-dimensional simulations consisting in three different conditions of jet impingement and compared the results to experimental data. This study was first dedicated to the establishment of the numerical configuration and the setting of the injection parameters of the jet. We studied the dynamics of air entrainment by the jets impacting on the surface of the water in a tank, from the creation of the aerated cavities to the motion of the bubble plumes resulting from their deterioration of the cavities. The results concerned time-dependent and transient phenomena. To validate the simulations, we made several comparisons with experimental data, considering three angles of jet impact. Finally, we compared two numerical models for the free-surface description, using the most prevalent method in the literature and an original free-surface tracking method recently developed in our numerical tool. We showed that the formation of air cavities was similar for each condition and each numerical model, in agreement with the experimental results. Moreover, it was observed that the air entrainment had a different behavior depending on the conditions of jet impact.
Estuarine, Coastal and Shelf Science, 2011
The study details new sediment concentration measurements associated with some turbulence charact... more The study details new sediment concentration measurements associated with some turbulence characterisation conducted at high frequency in the undular tidal bore of the Garonne River (France). Acoustic Doppler velocimetry was used, and the suspended sediment concentration was deduced from the acoustic backscatter intensity. The field data set demonstrated some unique flow features of the tidal bore including some large and rapid turbulent velocity fluctuations during and after the bore passage. Some unusually high suspended sediment concentration was observed about 100 s after the tidal bore front lasting for more than 10 minutes. It is thought that the tidal bore passage scoured the bed and convected upwards the bed material, reaching the free-surface after the bore passage. Behind the tidal bore, the net sediment flux magnitude was 30 times larger than the ebb tide net flux and directed upstream. A striking feature of the data set was the intense mixing and suspended sediment motion during the tidal bore and following flood tide. This feature has been rarely documented.
Advanced Numerical Modelling of Wave Structure Interactions, 2021