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Annie-claude Bayeul-lainé

Arts et Metiers ParisTech, Laboratoire De Mécanique De Lille, maitre de conférences

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SkillsFluid Mechanics, Numerical Simulation, Computational Fluid Dynamics, CFD Simulation, Fluid Turbulence, Vertical Axis Wind Turbine, Numerical Modeling, Computational Fluid Mechanics, Turbulence, Turbomachinery, Renewable Energy, Urban Renewal, Building Physics, Urban Energy, STAR-CCM , Fluid, Wind Energy, Wind Turbines, Wind, Aerodynamics, Modeling and Simulation, Numerical Analysis, Wind Engineering, Computational Simulation, Calculations, Analysis, Geometry, Thermal Engineering, Turbulence Modeling, Engineering Thermodynamics, CFX, Mechanical Engineering, Engineering Education, Higher Education, Environmental Engineering, Energy, Vortex, LES, CFD Coding, FLUENT, Modelisation, Flow, DES, Pressure, Coding, Models

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Papers by Annie-claude Bayeul-lainé

Investigations on the use of a KFm-4 profile to improve the energy extraction performance of a fully-activated flapping foil

Ocean engineering, Mar 1, 2024

Numerical investigations on unsteady vortical flows and separation-induced transition over a cycloidal rotor at low Reynolds number

Energy Conversion and Management, Aug 1, 2022

The unsteady vortical flows and laminar-turbulence transition over a 2-bladed cycloidal rotor are... more The unsteady vortical flows and laminar-turbulence transition over a 2-bladed cycloidal rotor are investigated numerically at two advance coefficients, with special emphasis on the influence of two turbulence models, namely the original SST k-ω model and SST γ-Re θt transition model. The numerical results are compared with the existing numerical and experimental data, in terms of the global performance and detailed internal flow structures. The primary results show that increasing the advanced coefficient can't change the transition location of the performance for the single blade, but the magnitudes of these variables. Then, combined the forces acting on two blades and the blade loadings, the difference of the vertical force and propulsive force of the rotating system and single blade are clarified clearly for two turbulence models. Finally, at advancing side, the transition and its evolution on a single blade is elaborated. It shows that the SST γ-Re θt transition model is superior in predicting the overall performance, and is highly subjected to the disturbances, characterized by the large-scale vortex structures and massive flow separation, compared with SST k-ω model. Simultaneously, it has the capability to capture the transition process, from growing waves of the laminar boundary layer induced by the roll-up vortices to the fully generation of the separation bubble. It believes that this work can deep the understandings of underlying flow physics inside the cycloidal roto at low Reynolds number.

Numerical and experimental investigations in a vaned diffuser of SHF impeller

HAL (Le Centre pour la Communication Scientifique Directe), Aug 26, 2013

Le papier présente l'analyse des performances et de l'écoulement interne dans un diffuseur aubé d... more Le papier présente l'analyse des performances et de l'écoulement interne dans un diffuseur aubé d'une pompe centrifuge grâce à la technique PIV, aux sondes de pression et aux simulations numériques. Les mesures PIV ont été réalisées à différentes hauteurs dans un canal du diffuseur, pour une vitesse de rotation et différents débits. Dans chaque cas, les mesures PIV ont été effectuées pour différentes positions angulaires de la roue. Des sondes de pression trois trous ont également été utilisées dans le diffuseur à différentes positions radiales et axiales. Les simulations numériques ont été réalisées avec deux codes: i-Star CCM+ 7.02.011 (LML), ii-CFX 10.0 (Université de Padoue). Des comparaisons entre résultats numériques (modélisation instationnaire) et expérimentaux sont présentés et discutés pour deux débits. Les effets des pertes dues aux jeux entre parties fixes et partie tournante sont étudiés.

Numerical investigation of the effect of motion trajectory on the vortex shedding process behind a flapping airfoil

HAL (Le Centre pour la Communication Scientifique Directe), Dec 16, 2017

e e ect of non-sinusoidal trajectory on the propulsive performances and the vortex shedding proce... more e e ect of non-sinusoidal trajectory on the propulsive performances and the vortex shedding process behind a apping airfoil is investigated in this sutdy. A movement of a rigid NACA 0012 airfoil undergoing a combined heaving and pitching motions at low Reynolds number (11 000) is considered. An elliptic function with an adjustable parameter S (atness coe cient) is used to realize various non-sinusoidal trajectories. e two-dimensional unsteady and incompressible Navier-Stokes equation governing the ow over the apping airfoil is resolved using the commercial so ware STAR CCM+. It is shown that the combination of sinusoidal and non-sinusoidal apping motion has a great e ect on the propulsive performances of the apping airfoil. e maximum propulsive e ciency is always achievable with sinusoidal trajectories. However, non-sinusoidal trajectories are found to considerably improuvr the propulsive force up to 52% larger than its natural value. Flow visualization shows that the vortex shedding process and the wake structure are substantially altered under the non-sinusoidal trajectory e ect. Depending on the nature of the apping trajectory, several modes of vortex shedding are identi ed and presented in this paper.

Analysis of the cavitation instabilities with time-resolved stereo and multiplane particle image velocimetry

Physics of Fluids, Dec 1, 2022

The present paper is devoted to the analysis of the various instabilities of cavitation attached ... more The present paper is devoted to the analysis of the various instabilities of cavitation attached to a two-dimensional (2D) profile. Time resolved stereo Particle Image Velocimetry (PIV) was conducted in a small-scale 2D venturi type section, in different vertical planes in the streamwise direction, located at varying positions in the depth of the channel. These experiments enabled to obtain the time evolution of the three components of the velocity field in the cavitation area, and to derive the time-averaged gradients in the spanwise direction. Test cases at various Reynolds number were conducted, maintaining either the pressure or the cavitation number constant, to discuss the impact of these parameters on the flow. Then, the attention was focused on three distinct flow dynamics, namely sheet cavitation, where no large-scale instability can be detected, single cloud cavitation, where a large cloud of vapor is shed periodically at the rear of the cavity, and multi-cloud cavitation, where the process is more complex, as more than one clouds are shed downstream. The data reveal that the structure and the structure of the re-entrant jet, which is one of the primary mechanisms of cloud cavitation, is more complex than reported in the previous studies. Although the jet can be detected as an intermittent low speed reverse flow in the streamwise direction, it is actually made of successive vortices about the channel depth, which are convected downstream while expanding in the vertical direction, causing the cavity lift and thus contributing to its final split and the cloud shedding.

Unsteady Velocity Piv Measurements and 3D Numerical Calculation Compatisons Inside the Impeller of a Radial Pump Model

PIV measurements were performed at mid hub section inside the impeller of a vaned diffuser pump m... more PIV measurements were performed at mid hub section inside the impeller of a vaned diffuser pump model working with air. Several previous papers have already presented part of impeller flow characteristics mainly for vaneless diffuser and near nominal mass flow rate. This paper concerns the pump configuration where the diffuser blades interacted with the impeller flow. Each PIV measuring plane was related to one particular impeller blade to blade channel and analyzed according to different relative positions of the vaned diffuser. A fully unsteady calculation of the whole pump has been performed and comparisons between numerical and experimental results are presented and discussed for four different mass flow rates. The present analysis is restricted to the outlet section of the impeller blade to blade passage for one particular impeller blade position relative to the diffuser.

Analyses des instationnarités dans un diffuseur aubé de machine centrifuge et de leurs effets sur sa performance

Effects of Non-Sinusoidal Motion and Effective Angle of Attack on Energy Extraction Performance of a Fully-Activated Flapping Foil

Journal of Applied Fluid Mechanics, 2021

Flapping foil energy harvesting systems are considered as highly competitive devices for conventi... more Flapping foil energy harvesting systems are considered as highly competitive devices for conventional turbines. Several research projects have already been carried out to improve performances of such new devices. This paper is devoted to study effects of non-sinusoidal heaving trajectory, non-sinusoidal pitching trajectory, and the effective angle of attack on the energy extraction performances of a flapping foil operating at low Reynolds number (Re=1100). An elliptic function with an adjustable parameter S (flattening parameter) is used to simulate various sinusoidal and non-sinusoidal flapping trajectories. The flow around the flapping foil is simulated by solving Navier-Stokes equations using the commercial software Star CCM+ based on the finitevolume method. Overset mesh technique is used to model the flapping motion. The study is applied to the NACA0015 foil with the following kinetic parameters: a dimensionless heaving amplitude h0 = 1c, a shift angle between heaving and pitching motions  = 90°, a reduced frequency f * = 0.14, and an effective angle of attack αmax varying between 15° and 50°, corresponding to a pitching amplitude in the range 0 = 55.51° to 99.51°. The results show that, the non-sinusoidal trajectory affects considerably the energy extraction performances. For the reference case (sinusoidal heaving and pitching motions, Sh = S =1), best performances are obtained for the effective angle of attack, αmax = 40°. At small effective angle of attack αmax <30°, the non-sinusoidal pitching motion combined with a sinusoidal heaving motion, greatly improves energy extraction performances. For αmax = 15°, Sh = 1 and S = 2, energy extraction efficiency is improved by 52.22% and the power coefficient by 70.40% comparatively to sinusoidal pitching motion. At high effective angles of attack (αmax > 40°), non-sinusoidal pitching motion has a negative effect. Performances improvement is quite limited with the combined motions non-sinusoidal heaving/sinusoidal pitching.

Effect of pitching angle, pitch-pivot-point, blade camber and deflected sharp leading edge on performance and vortical flows of reversed pitching airfoils

Ocean Engineering, Jul 1, 2023

Leakage Flow Influence on SHF pump model performances

International Journal of Fluid Machinery and Systems, Sep 30, 2015

This paper deals with the influence of leakage flow existing in SHF pump model on the analysis of... more This paper deals with the influence of leakage flow existing in SHF pump model on the analysis of internal flow behaviour inside the vane diffuser of the pump model performance using both experiments and calculations. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given speed of rotation and various flow rates. For each operating condition, the PIV measurements have been trigged with different angular impeller positions. The performances and the static pressure rise of the diffuser were also measured using a three-hole probe. The numerical simulations were carried out with Star CCM+ 9.06 code (RANS frozen and unsteady calculations). Some results were already presented at the XXth IAHR Symposium for three flowrates for RANS frozen and URANS calculations. In the present paper, comparisons between URANS calculations with and without leakages and experimental results are presented and discussed for these flow rates. The performances of the diffuser obtained by numerical calculations are compared to those obtained by the three-holes probe measurements. The comparisons show the influence of fluid leakages on global performances and a real improvement concerning the efficiency of the diffuser, the pump and the velocity distributions. These results show that leakage is an important parameter that has to be taken into account in order to make improved comparisons between numerical approaches and experiments in such a specific model set up.

Two-phase numerical study of the flow field formed in water pump sump: influence of air entrainment

IOP conference series, Nov 26, 2012

In a pump sump it is imperative that the amount of non-homogenous flow and entrained air be kept ... more In a pump sump it is imperative that the amount of non-homogenous flow and entrained air be kept to a minimum. Free air-core vortex occurring at a water-intake pipe is an important problem encountered in hydraulic engineering. These vortices reduce pump performances, may have large effects on the operating conditions and lead to increase plant operating costs. The purpose of this paper is to reproduce the flow pattern of experiments and to confirm the geometrical parameter that influences the flow structure in such a pump. The numerical model solves the Reynolds averaged Navier-Stokes (RANS) equations and VOF multiphase model. STAR CCM+ with an adapted mesh configuration using hexahedral mesh with prism layer near walls was used. Attempts have been made to calculate two phase unsteady flow for stronger mass flow rates and stronger submergence with low water level in order to be able to capture air entrainment. The results allow the knowledge of some limits of numerical models, of mass flow rates and of submergences for air entrainment. In the validation of this numerical model, emphasis was placed on the prediction of the number, location, size and strength of the various types of vortices coming from the free surface.

Analysis of High Energy Impact of a Raindrop on Water

Springer eBooks, 2020

The present paper is devoted to the analysis of the impact of a raindrop on water. The studied co... more The present paper is devoted to the analysis of the impact of a raindrop on water. The studied configuration is focused on the effects of high energy splash regimes, caused by the impact of large droplets at high velocity. Such cases, which mimic raindrops falling on the surface of the ocean at their terminal speed, are characterized by short time scales and complex mechanisms, and they have received little attention until now. The GERRIS opensource solver is used to perform three-dimensional simulations of the impact. The capabilities of octree adaptative mesh refinement enable to capture the small-scale features of the flow, while the Volume Of Fluid (VOF) approach combined with a balanced force surface tension calculation is applied to advect the volume fraction of liquid and reconstruct the interfaces. A post-processing of the results has been developed to identify each object resulting from the splash and characterize their evolution in time. Specifically, the contour of the liquid/gas structure created at the impact is reconstructed as well as the size and position of the ligaments and droplets aerosolized in the atmosphere. The results are compared to experimental data obtained previously by Murphy et al. (J. Fluid Mech., vol. 780, pp. 536-577): both the crown formation above the cavity created by the impact, the ligaments emanating from the rim at the top of the crown, and the downward liquid jet that pierces through the bottom of the cavity, are correctly reproduced by the model. A very good quantitative agreement is also obtained regarding the time evolution of the crown dimensions, including its closure after the initial phase of expansion.

Analysis of flow-induced performance change of cycloidal rotors: Influence of pitching kinematic and chord-to-radius ratio

Ocean Engineering, Nov 1, 2022

As a new-type propulsive system, cycloidal rotor has been attracting more attention recently. The... more As a new-type propulsive system, cycloidal rotor has been attracting more attention recently. The present work concentrates on the analysis of the performance and internal flow field of a two-bladed cycloidal rotor operating at low Reynolds numbers, with special emphasis on understanding how the flow structure affects the performance at different working conditions. The symmetrical/asymmetrical pitching motions are evaluated initially and the primary results show that the asymmetrical pitching with a mean pitch angle of 5° improves the efficiency of the rotating system. Then, the effect of the chord-to-radius ratio at three different conditions is discussed, which shows that the chord-to-radius ratio of 0.45 is the best value to maximise the performance. The flow pattern, involving the blade-wake interaction, wake-wake interaction, three-vortex-structure on the blade surface, rollup vortices inside the laminar boundary layer, laminar separation bubble, leadingedge vortex, trailing-edge vortex and flow separation vortex, are discussed in detail for various operating conditions. The study of the performance of a single blade, the forces (lift and drag) distributions, the blade loadings and the near-wall flows on two blades, provide a new understanding of the global performance of the propeller.

An Experimental Study of the Flow Field Inside the Diffuser Passage of a Laboratory Centrifugal Pump

Journal of Fluids Engineering-transactions of The Asme, Jun 1, 2015

Experimental investigation on the performance analysis and internal flow characteristics inside t... more

Direct Numerical Simulation of Shallow Water Breaking Waves Generated by Wave Plate

HAL (Le Centre pour la Communication Scientifique Directe), Sep 1, 2022

We present direct numerical simulation of breaking waves in shallow water generated by the wave p... more We present direct numerical simulation of breaking waves in shallow water generated by the wave plate. The open-source Basilisk solver is used to solve the incompressible, variable-density, twophase Navier-Stokes equations with surface tension. The air-water interface is advected using a momentum-conservative Volume-of-Fluid (MC-VOF) scheme. The surface tension is treated with the balanced-force technique. Adaptive mesh refinement (AMR) scheme is employed for computational efficiency, concentrating the computational resource on the significant solution area. By reconstructing the piston-type wave plate numerically, we realize high-fidelity simulation of experimental waves under the wide-ranging motions of the wave plate. The relationship between varying maximum wave plate speed and associated maximum wave height before breaking is investigated, the onset of wave breaking as a function of the ratio of wave height to water depth is determined to distinguish between non-breaking waves, spilling breakers, and plunging breakers. A typical plunging breaking wave with a large ratio of wave height to water depth is initialized to recognize the wave breaking and air entrainment process. We obtain good collapse of the simulated free-surface evolution and velocity fields with respect to the experiment. The shape and size of air entrapped at impact by plunging jet matches closely the experimental observation during wave breaking. The time-evolving energy budget and bubble characteristics under breaking waves are further discussed based on the numerical results.

Unsteady flow field in a mini VAWT with relative rotation blades: analysis of temporal results

IOP conference series, Dec 20, 2013

Effect of time-varying freestream on performance and vortex dynamics of forward and reversed pitching airfoils

Journal of Fluids and Structures, Apr 1, 2022

The goal of the present work deals with the influence of the oscillating freestream on the global... more The goal of the present work deals with the influence of the oscillating freestream on the global performance, transition and vortex dynamics of forward and reversed airfoils. Three important parameters, involving the phase lag, oscillating amplitude and mean reduced frequency, are analyzed systematically. The primary results show that both the phase lag and oscillating amplitude have great impact on the transition and flow structures, depending on the instantaneous freestream Reynolds number. The reversed airfoil is more prone to being affected by these parameters, characterized by the earlier flow separation near the sharp leading edge and the more complex vortex shedding, compared with that over the forward airfoil. It shows that increasing the oscillating amplitude can improve the mean performance, but it decreases with the increase of the mean reduced frequency. Additionally, it is observed that there is a second transition on both two sides near the trailing edge of the reversed airfoil, which becomes weak when the instantaneous freestream Reynolds number is relatively low. Afterwards, the time-averaged performance of the reversed airfoil is better than forward airfoil at low reduced frequency, but it deteriorates dramatically with the increase of the reduced frequency. Furthermore, the transition and vortex evolution are delayed as the reduced frequency increases, and the delayed flow structures can be inferred from the velocity profiles in the wake region. Moreover, it can be seen that the velocity profile has a transition from the drag-indicative to thrust-indicative type when the reduced frequency increases, and the velocity variation in the vertical direction is more evident for the reversed airfoil due to the massive flow separation.

Investigations in a Vaned Diffuser of SHF Impeller

HAL (Le Centre pour la Communication Scientifique Directe), Jun 5, 2013

Numerical investigation of hemolysis phenomena in the FDA nozzle benchmark: mind the extensional stresses

HAL (Le Centre pour la Communication Scientifique Directe), Jun 1, 2022

In recent years, the idea of using a pump as a left ventricle assist device is being well develop... more In recent years, the idea of using a pump as a left ventricle assist device is being well developed by several groups. Meanwhile, one of the challenges in this field is the occurrence of biological phenomena such as hemolysis. From an engineering point of view, a solution to this problem is to provide an accurate and efficient numerical method to predict the phenomenon. Hemolysis models are typically based on equivalent scalar stress and exposure time. This paper aims to study the impact of considering extensional stresses as the main reason for hemolysis in the FDA Nozzle benchmark. The idea comes from an experimental article. First of all, flow's hemodynamic was validated by comparing the results of normalized axial velocity in several sections with the experimental data. In this case, three different RANS models k − , k −ω and k −ω SST were employed. As expected, it is clear that the k−ω SST is the most accurate model. In the next step, hemolysis simulations performed for different equivalent stresses. In this case, the impact of scaling up the extensional stresses on predicted hemolysis is studied by adding a coefficient C n to equivalent stress. It is concluded that by applying these new modifications the hemolysis index would be in a reliable range.

The importance of the knowledge of flow stream in water sump pump

HAL (Le Centre pour la Communication Scientifique Directe), Aug 26, 2013

De nombreuses méthodes expérimentales et numériques ont été développées en vue d'obtenir une meil... more De nombreuses méthodes expérimentales et numériques ont été développées en vue d'obtenir une meilleure description de l'écoulement interne dans les pompes. Ces calculs sont, en général, réalisés dans l'hypothèse de conditions aux limites uniformes et stationnaires, en particulier à l'aspiration. Cependant, peu d'études s'intéressent à des conditions aux limites non uniformes, particulièrement dans le cas des bassins d'aspiration des pompes. L'entrainement de tourbillons d'air dans les conduites d'aspiration est un problème important car ils réduisent les performances de la pompe. Le papier étudie l'écoulement du fluide dans le bassin d'aspiration. Des expériences ont été réalisées en vue de sélectionner la meilleure position du tuyau d'aspiration pour éviter l'apparition des tourbillons. Les études numériques tentent de reproduire le comportement du fluide dans le cas des expériences et de confirmer l'influence des paramètres géométriques sur la structure de l'écoulement dans le bassin. Ces études numériques ont mis en évidence la nécessité d'une modélisation instationnaire diphasique pour une meilleure compréhension des écoulements.

Investigations on the use of a KFm-4 profile to improve the energy extraction performance of a fully-activated flapping foil

Ocean engineering, Mar 1, 2024

Numerical investigations on unsteady vortical flows and separation-induced transition over a cycloidal rotor at low Reynolds number

Energy Conversion and Management, Aug 1, 2022

The unsteady vortical flows and laminar-turbulence transition over a 2-bladed cycloidal rotor are... more The unsteady vortical flows and laminar-turbulence transition over a 2-bladed cycloidal rotor are investigated numerically at two advance coefficients, with special emphasis on the influence of two turbulence models, namely the original SST k-ω model and SST γ-Re θt transition model. The numerical results are compared with the existing numerical and experimental data, in terms of the global performance and detailed internal flow structures. The primary results show that increasing the advanced coefficient can't change the transition location of the performance for the single blade, but the magnitudes of these variables. Then, combined the forces acting on two blades and the blade loadings, the difference of the vertical force and propulsive force of the rotating system and single blade are clarified clearly for two turbulence models. Finally, at advancing side, the transition and its evolution on a single blade is elaborated. It shows that the SST γ-Re θt transition model is superior in predicting the overall performance, and is highly subjected to the disturbances, characterized by the large-scale vortex structures and massive flow separation, compared with SST k-ω model. Simultaneously, it has the capability to capture the transition process, from growing waves of the laminar boundary layer induced by the roll-up vortices to the fully generation of the separation bubble. It believes that this work can deep the understandings of underlying flow physics inside the cycloidal roto at low Reynolds number.

Numerical and experimental investigations in a vaned diffuser of SHF impeller

HAL (Le Centre pour la Communication Scientifique Directe), Aug 26, 2013

Le papier présente l'analyse des performances et de l'écoulement interne dans un diffuseur aubé d... more Le papier présente l'analyse des performances et de l'écoulement interne dans un diffuseur aubé d'une pompe centrifuge grâce à la technique PIV, aux sondes de pression et aux simulations numériques. Les mesures PIV ont été réalisées à différentes hauteurs dans un canal du diffuseur, pour une vitesse de rotation et différents débits. Dans chaque cas, les mesures PIV ont été effectuées pour différentes positions angulaires de la roue. Des sondes de pression trois trous ont également été utilisées dans le diffuseur à différentes positions radiales et axiales. Les simulations numériques ont été réalisées avec deux codes: i-Star CCM+ 7.02.011 (LML), ii-CFX 10.0 (Université de Padoue). Des comparaisons entre résultats numériques (modélisation instationnaire) et expérimentaux sont présentés et discutés pour deux débits. Les effets des pertes dues aux jeux entre parties fixes et partie tournante sont étudiés.

Numerical investigation of the effect of motion trajectory on the vortex shedding process behind a flapping airfoil

HAL (Le Centre pour la Communication Scientifique Directe), Dec 16, 2017

e e ect of non-sinusoidal trajectory on the propulsive performances and the vortex shedding proce... more e e ect of non-sinusoidal trajectory on the propulsive performances and the vortex shedding process behind a apping airfoil is investigated in this sutdy. A movement of a rigid NACA 0012 airfoil undergoing a combined heaving and pitching motions at low Reynolds number (11 000) is considered. An elliptic function with an adjustable parameter S (atness coe cient) is used to realize various non-sinusoidal trajectories. e two-dimensional unsteady and incompressible Navier-Stokes equation governing the ow over the apping airfoil is resolved using the commercial so ware STAR CCM+. It is shown that the combination of sinusoidal and non-sinusoidal apping motion has a great e ect on the propulsive performances of the apping airfoil. e maximum propulsive e ciency is always achievable with sinusoidal trajectories. However, non-sinusoidal trajectories are found to considerably improuvr the propulsive force up to 52% larger than its natural value. Flow visualization shows that the vortex shedding process and the wake structure are substantially altered under the non-sinusoidal trajectory e ect. Depending on the nature of the apping trajectory, several modes of vortex shedding are identi ed and presented in this paper.

Analysis of the cavitation instabilities with time-resolved stereo and multiplane particle image velocimetry

Physics of Fluids, Dec 1, 2022

The present paper is devoted to the analysis of the various instabilities of cavitation attached ... more The present paper is devoted to the analysis of the various instabilities of cavitation attached to a two-dimensional (2D) profile. Time resolved stereo Particle Image Velocimetry (PIV) was conducted in a small-scale 2D venturi type section, in different vertical planes in the streamwise direction, located at varying positions in the depth of the channel. These experiments enabled to obtain the time evolution of the three components of the velocity field in the cavitation area, and to derive the time-averaged gradients in the spanwise direction. Test cases at various Reynolds number were conducted, maintaining either the pressure or the cavitation number constant, to discuss the impact of these parameters on the flow. Then, the attention was focused on three distinct flow dynamics, namely sheet cavitation, where no large-scale instability can be detected, single cloud cavitation, where a large cloud of vapor is shed periodically at the rear of the cavity, and multi-cloud cavitation, where the process is more complex, as more than one clouds are shed downstream. The data reveal that the structure and the structure of the re-entrant jet, which is one of the primary mechanisms of cloud cavitation, is more complex than reported in the previous studies. Although the jet can be detected as an intermittent low speed reverse flow in the streamwise direction, it is actually made of successive vortices about the channel depth, which are convected downstream while expanding in the vertical direction, causing the cavity lift and thus contributing to its final split and the cloud shedding.

Unsteady Velocity Piv Measurements and 3D Numerical Calculation Compatisons Inside the Impeller of a Radial Pump Model

PIV measurements were performed at mid hub section inside the impeller of a vaned diffuser pump m... more PIV measurements were performed at mid hub section inside the impeller of a vaned diffuser pump model working with air. Several previous papers have already presented part of impeller flow characteristics mainly for vaneless diffuser and near nominal mass flow rate. This paper concerns the pump configuration where the diffuser blades interacted with the impeller flow. Each PIV measuring plane was related to one particular impeller blade to blade channel and analyzed according to different relative positions of the vaned diffuser. A fully unsteady calculation of the whole pump has been performed and comparisons between numerical and experimental results are presented and discussed for four different mass flow rates. The present analysis is restricted to the outlet section of the impeller blade to blade passage for one particular impeller blade position relative to the diffuser.

Analyses des instationnarités dans un diffuseur aubé de machine centrifuge et de leurs effets sur sa performance

Effects of Non-Sinusoidal Motion and Effective Angle of Attack on Energy Extraction Performance of a Fully-Activated Flapping Foil

Journal of Applied Fluid Mechanics, 2021

Flapping foil energy harvesting systems are considered as highly competitive devices for conventi... more Flapping foil energy harvesting systems are considered as highly competitive devices for conventional turbines. Several research projects have already been carried out to improve performances of such new devices. This paper is devoted to study effects of non-sinusoidal heaving trajectory, non-sinusoidal pitching trajectory, and the effective angle of attack on the energy extraction performances of a flapping foil operating at low Reynolds number (Re=1100). An elliptic function with an adjustable parameter S (flattening parameter) is used to simulate various sinusoidal and non-sinusoidal flapping trajectories. The flow around the flapping foil is simulated by solving Navier-Stokes equations using the commercial software Star CCM+ based on the finitevolume method. Overset mesh technique is used to model the flapping motion. The study is applied to the NACA0015 foil with the following kinetic parameters: a dimensionless heaving amplitude h0 = 1c, a shift angle between heaving and pitching motions  = 90°, a reduced frequency f * = 0.14, and an effective angle of attack αmax varying between 15° and 50°, corresponding to a pitching amplitude in the range 0 = 55.51° to 99.51°. The results show that, the non-sinusoidal trajectory affects considerably the energy extraction performances. For the reference case (sinusoidal heaving and pitching motions, Sh = S =1), best performances are obtained for the effective angle of attack, αmax = 40°. At small effective angle of attack αmax <30°, the non-sinusoidal pitching motion combined with a sinusoidal heaving motion, greatly improves energy extraction performances. For αmax = 15°, Sh = 1 and S = 2, energy extraction efficiency is improved by 52.22% and the power coefficient by 70.40% comparatively to sinusoidal pitching motion. At high effective angles of attack (αmax > 40°), non-sinusoidal pitching motion has a negative effect. Performances improvement is quite limited with the combined motions non-sinusoidal heaving/sinusoidal pitching.

Effect of pitching angle, pitch-pivot-point, blade camber and deflected sharp leading edge on performance and vortical flows of reversed pitching airfoils

Ocean Engineering, Jul 1, 2023

Leakage Flow Influence on SHF pump model performances

International Journal of Fluid Machinery and Systems, Sep 30, 2015

This paper deals with the influence of leakage flow existing in SHF pump model on the analysis of... more This paper deals with the influence of leakage flow existing in SHF pump model on the analysis of internal flow behaviour inside the vane diffuser of the pump model performance using both experiments and calculations. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given speed of rotation and various flow rates. For each operating condition, the PIV measurements have been trigged with different angular impeller positions. The performances and the static pressure rise of the diffuser were also measured using a three-hole probe. The numerical simulations were carried out with Star CCM+ 9.06 code (RANS frozen and unsteady calculations). Some results were already presented at the XXth IAHR Symposium for three flowrates for RANS frozen and URANS calculations. In the present paper, comparisons between URANS calculations with and without leakages and experimental results are presented and discussed for these flow rates. The performances of the diffuser obtained by numerical calculations are compared to those obtained by the three-holes probe measurements. The comparisons show the influence of fluid leakages on global performances and a real improvement concerning the efficiency of the diffuser, the pump and the velocity distributions. These results show that leakage is an important parameter that has to be taken into account in order to make improved comparisons between numerical approaches and experiments in such a specific model set up.

Two-phase numerical study of the flow field formed in water pump sump: influence of air entrainment

IOP conference series, Nov 26, 2012

In a pump sump it is imperative that the amount of non-homogenous flow and entrained air be kept ... more In a pump sump it is imperative that the amount of non-homogenous flow and entrained air be kept to a minimum. Free air-core vortex occurring at a water-intake pipe is an important problem encountered in hydraulic engineering. These vortices reduce pump performances, may have large effects on the operating conditions and lead to increase plant operating costs. The purpose of this paper is to reproduce the flow pattern of experiments and to confirm the geometrical parameter that influences the flow structure in such a pump. The numerical model solves the Reynolds averaged Navier-Stokes (RANS) equations and VOF multiphase model. STAR CCM+ with an adapted mesh configuration using hexahedral mesh with prism layer near walls was used. Attempts have been made to calculate two phase unsteady flow for stronger mass flow rates and stronger submergence with low water level in order to be able to capture air entrainment. The results allow the knowledge of some limits of numerical models, of mass flow rates and of submergences for air entrainment. In the validation of this numerical model, emphasis was placed on the prediction of the number, location, size and strength of the various types of vortices coming from the free surface.

Analysis of High Energy Impact of a Raindrop on Water

Springer eBooks, 2020

The present paper is devoted to the analysis of the impact of a raindrop on water. The studied co... more The present paper is devoted to the analysis of the impact of a raindrop on water. The studied configuration is focused on the effects of high energy splash regimes, caused by the impact of large droplets at high velocity. Such cases, which mimic raindrops falling on the surface of the ocean at their terminal speed, are characterized by short time scales and complex mechanisms, and they have received little attention until now. The GERRIS opensource solver is used to perform three-dimensional simulations of the impact. The capabilities of octree adaptative mesh refinement enable to capture the small-scale features of the flow, while the Volume Of Fluid (VOF) approach combined with a balanced force surface tension calculation is applied to advect the volume fraction of liquid and reconstruct the interfaces. A post-processing of the results has been developed to identify each object resulting from the splash and characterize their evolution in time. Specifically, the contour of the liquid/gas structure created at the impact is reconstructed as well as the size and position of the ligaments and droplets aerosolized in the atmosphere. The results are compared to experimental data obtained previously by Murphy et al. (J. Fluid Mech., vol. 780, pp. 536-577): both the crown formation above the cavity created by the impact, the ligaments emanating from the rim at the top of the crown, and the downward liquid jet that pierces through the bottom of the cavity, are correctly reproduced by the model. A very good quantitative agreement is also obtained regarding the time evolution of the crown dimensions, including its closure after the initial phase of expansion.

Analysis of flow-induced performance change of cycloidal rotors: Influence of pitching kinematic and chord-to-radius ratio

Ocean Engineering, Nov 1, 2022

As a new-type propulsive system, cycloidal rotor has been attracting more attention recently. The... more As a new-type propulsive system, cycloidal rotor has been attracting more attention recently. The present work concentrates on the analysis of the performance and internal flow field of a two-bladed cycloidal rotor operating at low Reynolds numbers, with special emphasis on understanding how the flow structure affects the performance at different working conditions. The symmetrical/asymmetrical pitching motions are evaluated initially and the primary results show that the asymmetrical pitching with a mean pitch angle of 5° improves the efficiency of the rotating system. Then, the effect of the chord-to-radius ratio at three different conditions is discussed, which shows that the chord-to-radius ratio of 0.45 is the best value to maximise the performance. The flow pattern, involving the blade-wake interaction, wake-wake interaction, three-vortex-structure on the blade surface, rollup vortices inside the laminar boundary layer, laminar separation bubble, leadingedge vortex, trailing-edge vortex and flow separation vortex, are discussed in detail for various operating conditions. The study of the performance of a single blade, the forces (lift and drag) distributions, the blade loadings and the near-wall flows on two blades, provide a new understanding of the global performance of the propeller.

An Experimental Study of the Flow Field Inside the Diffuser Passage of a Laboratory Centrifugal Pump

Journal of Fluids Engineering-transactions of The Asme, Jun 1, 2015

Experimental investigation on the performance analysis and internal flow characteristics inside t... more

Direct Numerical Simulation of Shallow Water Breaking Waves Generated by Wave Plate

HAL (Le Centre pour la Communication Scientifique Directe), Sep 1, 2022

We present direct numerical simulation of breaking waves in shallow water generated by the wave p... more We present direct numerical simulation of breaking waves in shallow water generated by the wave plate. The open-source Basilisk solver is used to solve the incompressible, variable-density, twophase Navier-Stokes equations with surface tension. The air-water interface is advected using a momentum-conservative Volume-of-Fluid (MC-VOF) scheme. The surface tension is treated with the balanced-force technique. Adaptive mesh refinement (AMR) scheme is employed for computational efficiency, concentrating the computational resource on the significant solution area. By reconstructing the piston-type wave plate numerically, we realize high-fidelity simulation of experimental waves under the wide-ranging motions of the wave plate. The relationship between varying maximum wave plate speed and associated maximum wave height before breaking is investigated, the onset of wave breaking as a function of the ratio of wave height to water depth is determined to distinguish between non-breaking waves, spilling breakers, and plunging breakers. A typical plunging breaking wave with a large ratio of wave height to water depth is initialized to recognize the wave breaking and air entrainment process. We obtain good collapse of the simulated free-surface evolution and velocity fields with respect to the experiment. The shape and size of air entrapped at impact by plunging jet matches closely the experimental observation during wave breaking. The time-evolving energy budget and bubble characteristics under breaking waves are further discussed based on the numerical results.

Unsteady flow field in a mini VAWT with relative rotation blades: analysis of temporal results

IOP conference series, Dec 20, 2013

Effect of time-varying freestream on performance and vortex dynamics of forward and reversed pitching airfoils

Journal of Fluids and Structures, Apr 1, 2022

The goal of the present work deals with the influence of the oscillating freestream on the global... more The goal of the present work deals with the influence of the oscillating freestream on the global performance, transition and vortex dynamics of forward and reversed airfoils. Three important parameters, involving the phase lag, oscillating amplitude and mean reduced frequency, are analyzed systematically. The primary results show that both the phase lag and oscillating amplitude have great impact on the transition and flow structures, depending on the instantaneous freestream Reynolds number. The reversed airfoil is more prone to being affected by these parameters, characterized by the earlier flow separation near the sharp leading edge and the more complex vortex shedding, compared with that over the forward airfoil. It shows that increasing the oscillating amplitude can improve the mean performance, but it decreases with the increase of the mean reduced frequency. Additionally, it is observed that there is a second transition on both two sides near the trailing edge of the reversed airfoil, which becomes weak when the instantaneous freestream Reynolds number is relatively low. Afterwards, the time-averaged performance of the reversed airfoil is better than forward airfoil at low reduced frequency, but it deteriorates dramatically with the increase of the reduced frequency. Furthermore, the transition and vortex evolution are delayed as the reduced frequency increases, and the delayed flow structures can be inferred from the velocity profiles in the wake region. Moreover, it can be seen that the velocity profile has a transition from the drag-indicative to thrust-indicative type when the reduced frequency increases, and the velocity variation in the vertical direction is more evident for the reversed airfoil due to the massive flow separation.

Investigations in a Vaned Diffuser of SHF Impeller

HAL (Le Centre pour la Communication Scientifique Directe), Jun 5, 2013

Numerical investigation of hemolysis phenomena in the FDA nozzle benchmark: mind the extensional stresses

HAL (Le Centre pour la Communication Scientifique Directe), Jun 1, 2022

In recent years, the idea of using a pump as a left ventricle assist device is being well develop... more In recent years, the idea of using a pump as a left ventricle assist device is being well developed by several groups. Meanwhile, one of the challenges in this field is the occurrence of biological phenomena such as hemolysis. From an engineering point of view, a solution to this problem is to provide an accurate and efficient numerical method to predict the phenomenon. Hemolysis models are typically based on equivalent scalar stress and exposure time. This paper aims to study the impact of considering extensional stresses as the main reason for hemolysis in the FDA Nozzle benchmark. The idea comes from an experimental article. First of all, flow's hemodynamic was validated by comparing the results of normalized axial velocity in several sections with the experimental data. In this case, three different RANS models k − , k −ω and k −ω SST were employed. As expected, it is clear that the k−ω SST is the most accurate model. In the next step, hemolysis simulations performed for different equivalent stresses. In this case, the impact of scaling up the extensional stresses on predicted hemolysis is studied by adding a coefficient C n to equivalent stress. It is concluded that by applying these new modifications the hemolysis index would be in a reliable range.

The importance of the knowledge of flow stream in water sump pump

HAL (Le Centre pour la Communication Scientifique Directe), Aug 26, 2013

De nombreuses méthodes expérimentales et numériques ont été développées en vue d'obtenir une meil... more De nombreuses méthodes expérimentales et numériques ont été développées en vue d'obtenir une meilleure description de l'écoulement interne dans les pompes. Ces calculs sont, en général, réalisés dans l'hypothèse de conditions aux limites uniformes et stationnaires, en particulier à l'aspiration. Cependant, peu d'études s'intéressent à des conditions aux limites non uniformes, particulièrement dans le cas des bassins d'aspiration des pompes. L'entrainement de tourbillons d'air dans les conduites d'aspiration est un problème important car ils réduisent les performances de la pompe. Le papier étudie l'écoulement du fluide dans le bassin d'aspiration. Des expériences ont été réalisées en vue de sélectionner la meilleure position du tuyau d'aspiration pour éviter l'apparition des tourbillons. Les études numériques tentent de reproduire le comportement du fluide dans le cas des expériences et de confirmer l'influence des paramètres géométriques sur la structure de l'écoulement dans le bassin. Ces études numériques ont mis en évidence la nécessité d'une modélisation instationnaire diphasique pour une meilleure compréhension des écoulements.