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http://hdl.handle.net/10985/22706
Direct Numerical Simulation of Shallow Water Breaking Waves Generated by Wave Plate
LIU, Shuo; WANG, Hui; BAYEUL-LAINÉ, Annie-Claude; COUTIER-DELGOSHA, Olivier
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 (MCVOF) 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.
Thu, 01 Sep 2022 00:00:00 GMThttp://hdl.handle.net/10985/227062022-09-01T00:00:00ZLIU, ShuoWANG, HuiBAYEUL-LAINÉ, Annie-ClaudeCOUTIER-DELGOSHA, OlivierWe 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 (MCVOF) 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.Numerical investigation of hemolysis phenomena in the FDA nozzle benchmark : mind the extensional stresses
http://hdl.handle.net/10985/22617
Numerical investigation of hemolysis phenomena in the FDA nozzle benchmark : mind the extensional stresses
MAGHOULI, Ali; BAYEUL-LAINÉ, Annie-Claude; SIMONET, Sophie; HADDADI, Mohammad; COUTIER-DELGOSHA, Olivier
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 Cn to equivalent stress. It is concluded that by
applying these new modifications the hemolysis index would be in a reliable range.
Wed, 01 Jun 2022 00:00:00 GMThttp://hdl.handle.net/10985/226172022-06-01T00:00:00ZMAGHOULI, AliBAYEUL-LAINÉ, Annie-ClaudeSIMONET, SophieHADDADI, MohammadCOUTIER-DELGOSHA, OlivierIn 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 Cn to equivalent stress. It is concluded that by
applying these new modifications the hemolysis index would be in a reliable range.Approach of Dynamic Modelling of a Hydraulic System
http://hdl.handle.net/10985/21658
Approach of Dynamic Modelling of a Hydraulic System
RATOLOJANAHARY, Naly; GONZALEZ-VIEYRA, Joel-A; DUPONT, Patrick; BAYEUL-LAINE, Annie-Claude; SUEUR, Christophe; NEU, Thibault; GUYOMARC’H, David
In response to environmental degradation, particularly due to greenhouse gas emissions, renewable energy is increasing significantly today. Their development is also a major concern with regard to the depletion of non-renewable energies. However, their use is limited due to the instability induced in the electrical grid. Energy storage aims to regulate these fluctuations and thus smooth electricity production. Compressed air energy storage (CAES) is a type of high-capacity, low-cost energy storage on the market. REMORA, the storage system studied here is an underwater isothermal CAES system. This innovative system consists of compressing and relaxing the air in a quasi-isothermal way using liquid pistons. This method minimizes overall energy loss by maximizing heat transfer during air compressions and expansions. Compressed air is stored in underwater tanks and takes advantage of the hydrostatic pressure associated with the depthof the water. The architecture and operation of the hydraulic system are specific in order to maximize performance. During the energy storage and restitution processes, the exchange flow become transient due to several valve commutations. It occurs frequently during REMORA hydraulic system operation. Modeling the system become complex. A simple example of a hydroelectric plant, similar to the case study, is modeled using two different software. The results show the most appropriate tool, to model the hydraulic system, with an integrated approach based on dynamic modeling.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10985/216582020-01-01T00:00:00ZRATOLOJANAHARY, NalyGONZALEZ-VIEYRA, Joel-ADUPONT, PatrickBAYEUL-LAINE, Annie-ClaudeSUEUR, ChristopheNEU, ThibaultGUYOMARC’H, DavidIn response to environmental degradation, particularly due to greenhouse gas emissions, renewable energy is increasing significantly today. Their development is also a major concern with regard to the depletion of non-renewable energies. However, their use is limited due to the instability induced in the electrical grid. Energy storage aims to regulate these fluctuations and thus smooth electricity production. Compressed air energy storage (CAES) is a type of high-capacity, low-cost energy storage on the market. REMORA, the storage system studied here is an underwater isothermal CAES system. This innovative system consists of compressing and relaxing the air in a quasi-isothermal way using liquid pistons. This method minimizes overall energy loss by maximizing heat transfer during air compressions and expansions. Compressed air is stored in underwater tanks and takes advantage of the hydrostatic pressure associated with the depthof the water. The architecture and operation of the hydraulic system are specific in order to maximize performance. During the energy storage and restitution processes, the exchange flow become transient due to several valve commutations. It occurs frequently during REMORA hydraulic system operation. Modeling the system become complex. A simple example of a hydroelectric plant, similar to the case study, is modeled using two different software. The results show the most appropriate tool, to model the hydraulic system, with an integrated approach based on dynamic modeling.Numerical investigations on unsteady vortical flows and separation-induced transition over a cycloidal rotor at low Reynolds number
http://hdl.handle.net/10985/22618
Numerical investigations on unsteady vortical flows and separation-induced transition over a cycloidal rotor at low Reynolds number
SHI, Lei; BAYEUL-LAINE, Annie-Claude; COUTIER-DELGOSHA, Olivier
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-Reθt 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-Reθt 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.
Mon, 01 Aug 2022 00:00:00 GMThttp://hdl.handle.net/10985/226182022-08-01T00:00:00ZSHI, LeiBAYEUL-LAINE, Annie-ClaudeCOUTIER-DELGOSHA, OlivierThe 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-Reθt 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-Reθt 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.Analysis of flow-induced performance change of cycloidal rotors: Influence of pitching kinematic and chord-to-radius ratio
http://hdl.handle.net/10985/22677
Analysis of flow-induced performance change of cycloidal rotors: Influence of pitching kinematic and chord-to-radius ratio
SHI, Lei; BAYEUL-LAINÉ, Annie-Claude; COUTIER-DELGOSHA, Olivier
As a new type of the propulsive devices, 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 pitching 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 structures on the blade
surface, roll-up vortices inside the laminar boundary layer, separation bubble, leading-edge vortex, trailing-edge
vortex and flow separation vortex, are discussed in detail under various operating conditions. The study on 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 change of the propeller.
Mon, 01 Aug 2022 00:00:00 GMThttp://hdl.handle.net/10985/226772022-08-01T00:00:00ZSHI, LeiBAYEUL-LAINÉ, Annie-ClaudeCOUTIER-DELGOSHA, OlivierAs a new type of the propulsive devices, 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 pitching 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 structures on the blade
surface, roll-up vortices inside the laminar boundary layer, separation bubble, leading-edge vortex, trailing-edge
vortex and flow separation vortex, are discussed in detail under various operating conditions. The study on 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 change of the propeller.Analysis of High Energy Impact of a Raindrop on Water
http://hdl.handle.net/10985/21877
Analysis of High Energy Impact of a Raindrop on Water
GHANDOUR, Mohamed Houssein; BAYEUL-LAINE, Annie-Claude; COUTIER-DELGOSHA, Olivier
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.
Sun, 26 Jul 2020 00:00:00 GMThttp://hdl.handle.net/10985/218772020-07-26T00:00:00ZGHANDOUR, Mohamed HousseinBAYEUL-LAINE, Annie-ClaudeCOUTIER-DELGOSHA, OlivierThe 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.Investigations on vortex evolution and wake dynamics of bio-inspired pitching hydrofoils
http://hdl.handle.net/10985/23044
Investigations on vortex evolution and wake dynamics of bio-inspired pitching hydrofoils
WANG, Yefang; SHI, Lei; BAYEUL-LAINÉ, Annie-Claude; COUTIER-DELGOSHA, Olivier
Recently, lots of oscillating targets inspired from motions of some insects and birds have been applied extensively to many engineering applications. The aim of this work is to reveal the performance and detailed flow structures over the pitching corrugated hydrofoils under various working conditions, using the SST [Formula: see text] transition model. First of all, the lift coefficients of a smooth oscillating airfoil at different reduced frequency and pitching angles show a good agreement with the experiments, characterized by the accurate prediction of the light and deep stall. For the pitching corrugated hydrofoils, it shows that the mean lift coefficient increases with the pitching magnitude, but it has an obvious drop at high reduced frequency for the case with large pitching amplitude, which is mainly induced by the pressure modification on the surface with smooth curvature, depending on the oscillation significantly. In addition, the mean drag coefficient also indicates that the drag turns into the thrust at high reduced frequency when the pitching amplitude exceeds to the value of 10°. Increasing the reduced frequency delays the flow structure and leads to the deflection of the wake vortical flow. The Reynolds number also has an impact on the hydrofoil performance and wake morphology. Furthermore, regarding the shape effect, it seems that hydrofoil A (consisting of two protrusions and hollows and the aft part with smooth curvature) achieves the higher lift than hydrofoil B (comprising several protrusions and hollows along the surface), specially at high reduced frequency. Although the frequency collected from two hydrofoils remains nearly the same near the leading edge and in the wake region, the high sub-frequency is evidently reduced for hydrofoil B in second and third hollows, due to the relatively stable trapped vortices. Then, the wake transition from the thrust-indicative to drag-indicative profile for hydrofoil B is also slower compared with hydrofoil A. Finally, it is observed that with the increase of the thickness, the lift/drag ratio decreases and the slow wake transition is detected for the thin hydrofoil, which is associated with the relatively low drag coefficient.
Tue, 01 Nov 2022 00:00:00 GMThttp://hdl.handle.net/10985/230442022-11-01T00:00:00ZWANG, YefangSHI, LeiBAYEUL-LAINÉ, Annie-ClaudeCOUTIER-DELGOSHA, OlivierRecently, lots of oscillating targets inspired from motions of some insects and birds have been applied extensively to many engineering applications. The aim of this work is to reveal the performance and detailed flow structures over the pitching corrugated hydrofoils under various working conditions, using the SST [Formula: see text] transition model. First of all, the lift coefficients of a smooth oscillating airfoil at different reduced frequency and pitching angles show a good agreement with the experiments, characterized by the accurate prediction of the light and deep stall. For the pitching corrugated hydrofoils, it shows that the mean lift coefficient increases with the pitching magnitude, but it has an obvious drop at high reduced frequency for the case with large pitching amplitude, which is mainly induced by the pressure modification on the surface with smooth curvature, depending on the oscillation significantly. In addition, the mean drag coefficient also indicates that the drag turns into the thrust at high reduced frequency when the pitching amplitude exceeds to the value of 10°. Increasing the reduced frequency delays the flow structure and leads to the deflection of the wake vortical flow. The Reynolds number also has an impact on the hydrofoil performance and wake morphology. Furthermore, regarding the shape effect, it seems that hydrofoil A (consisting of two protrusions and hollows and the aft part with smooth curvature) achieves the higher lift than hydrofoil B (comprising several protrusions and hollows along the surface), specially at high reduced frequency. Although the frequency collected from two hydrofoils remains nearly the same near the leading edge and in the wake region, the high sub-frequency is evidently reduced for hydrofoil B in second and third hollows, due to the relatively stable trapped vortices. Then, the wake transition from the thrust-indicative to drag-indicative profile for hydrofoil B is also slower compared with hydrofoil A. Finally, it is observed that with the increase of the thickness, the lift/drag ratio decreases and the slow wake transition is detected for the thin hydrofoil, which is associated with the relatively low drag coefficient.Analysis of the cavitation instabilities with time-resolved stereo and multiplane Particle Image Velocimetry
http://hdl.handle.net/10985/23042
Analysis of the cavitation instabilities with time-resolved stereo and multiplane Particle Image Velocimetry
LONG, Kunpeng; GE, Mingming; BAYEUL-LAINÉ, Annie-Claude; COUTIER-DELGOSHA, Olivier
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
Tue, 01 Nov 2022 00:00:00 GMThttp://hdl.handle.net/10985/230422022-11-01T00:00:00ZLONG, KunpengGE, MingmingBAYEUL-LAINÉ, Annie-ClaudeCOUTIER-DELGOSHA, OlivierThe 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 sheddingParametrical study on separation-induced transition and vortex dynamics of a reversed pitching airfoil
http://hdl.handle.net/10985/23043
Parametrical study on separation-induced transition and vortex dynamics of a reversed pitching airfoil
SHI, Lei; WANG, Yefang; ZHANG, Desheng; BAYEUL-LAINÉ, Annie-Claude; COUTIER-DELGOSHA, Olivier
The pitching airfoils, applied to the vertical axis turbines and propellers, are critical to extract more energy from the environment. At retreating side, when the airfoil blunt leading edge becomes the trailing edge, the transition and vortex dynamics are quite different from that at advancing side. The goal of the present work is to investigate the transition and vortex evolution over the reversed pitching airfoil, with main focus on the parametrical effect, including the mean pitching angle and pitching amplitude, reduced frequency and Reynolds number. The main results show that the flow structure on the reversed airfoil is more complex compared with that over the forward airfoil due to the earlier flow separation near the sharp leading edge. Then, the transition on the reversed airfoil firstly occurs within the separated shear layer near the sharp leading edge, and then the flow reattaches, leading to the generation of the leading-edge vortex. Near the blunt trailing edge, the second transition appears on two sides, resulting in the asymmetrical boundary layer as the incidence increases continuously. This event is totally different from that on the forward airfoil, shown by the transition always moving from the trailing edge to the leading edge. The flow unsteadiness of the reversed airfoil is mainly induced by the separated shear layer and leading-edge vortex, which is greatly affected by different parameters. Besides, the trajectory of some specific vortices also depends on the working conditions significantly. It is believed that this work can deepen the understandings of underlying flow physics of the reversed airfoils.
Tue, 01 Nov 2022 00:00:00 GMThttp://hdl.handle.net/10985/230432022-11-01T00:00:00ZSHI, LeiWANG, YefangZHANG, DeshengBAYEUL-LAINÉ, Annie-ClaudeCOUTIER-DELGOSHA, OlivierThe pitching airfoils, applied to the vertical axis turbines and propellers, are critical to extract more energy from the environment. At retreating side, when the airfoil blunt leading edge becomes the trailing edge, the transition and vortex dynamics are quite different from that at advancing side. The goal of the present work is to investigate the transition and vortex evolution over the reversed pitching airfoil, with main focus on the parametrical effect, including the mean pitching angle and pitching amplitude, reduced frequency and Reynolds number. The main results show that the flow structure on the reversed airfoil is more complex compared with that over the forward airfoil due to the earlier flow separation near the sharp leading edge. Then, the transition on the reversed airfoil firstly occurs within the separated shear layer near the sharp leading edge, and then the flow reattaches, leading to the generation of the leading-edge vortex. Near the blunt trailing edge, the second transition appears on two sides, resulting in the asymmetrical boundary layer as the incidence increases continuously. This event is totally different from that on the forward airfoil, shown by the transition always moving from the trailing edge to the leading edge. The flow unsteadiness of the reversed airfoil is mainly induced by the separated shear layer and leading-edge vortex, which is greatly affected by different parameters. Besides, the trajectory of some specific vortices also depends on the working conditions significantly. It is believed that this work can deepen the understandings of underlying flow physics of the reversed airfoils.Analysis of the Unsteady Flow Around a Hydrofoil at Various Incidences
http://hdl.handle.net/10985/21657
Analysis of the Unsteady Flow Around a Hydrofoil at Various Incidences
SHI, Lei; BAYEUL-LAINÉ, Annie-Claude; COUTIER-DELGOSHA, Olivier
The oscillating hydrofoils used in underwater propulsion devices often experience large variations of the flow incidence, which favors cavitation at large angle of attack, and therefore a severe degradation of the performance, additional flow instability, and even cavitation erosion. These various phenomena make numerical simulations of the flow around oscillating hydrofoils quite challenging, especially in cases where the laminar-turbulent transition usually occurs when the blade has a high angle of attack. In the present study, the unsteady flow around a stationary Clark-Y hydrofoil is simulated at five fix incidence angles using the Star CCM+ software. The results show that the lift coefficient increases continuously with the incidence angle up to 15°, even after a separation vortex is generated near the trailing edge. Then, as a slight stall occurs at 20°, the lift coefficients obtained with the k-ω SST and SST Re teta transition models become significantly different, mostly because of the different prediction of laminar to turbulence transition at the hydrofoil leading edge. Under deep stall condition at 25°, the flow is much more complex and the hydrofoil performance decreases dramatically. The lift force predicted by the SST transition model is more periodic than with the SST k-ω model. Although the general vortex evolution predicted by the two turbulence models is similar, the local pressure experiences larger amplitude variations with the k-ω SST model, as can be also observed from the evolution of the lift coefficient.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10985/216572020-01-01T00:00:00ZSHI, LeiBAYEUL-LAINÉ, Annie-ClaudeCOUTIER-DELGOSHA, OlivierThe oscillating hydrofoils used in underwater propulsion devices often experience large variations of the flow incidence, which favors cavitation at large angle of attack, and therefore a severe degradation of the performance, additional flow instability, and even cavitation erosion. These various phenomena make numerical simulations of the flow around oscillating hydrofoils quite challenging, especially in cases where the laminar-turbulent transition usually occurs when the blade has a high angle of attack. In the present study, the unsteady flow around a stationary Clark-Y hydrofoil is simulated at five fix incidence angles using the Star CCM+ software. The results show that the lift coefficient increases continuously with the incidence angle up to 15°, even after a separation vortex is generated near the trailing edge. Then, as a slight stall occurs at 20°, the lift coefficients obtained with the k-ω SST and SST Re teta transition models become significantly different, mostly because of the different prediction of laminar to turbulence transition at the hydrofoil leading edge. Under deep stall condition at 25°, the flow is much more complex and the hydrofoil performance decreases dramatically. The lift force predicted by the SST transition model is more periodic than with the SST k-ω model. Although the general vortex evolution predicted by the two turbulence models is similar, the local pressure experiences larger amplitude variations with the k-ω SST model, as can be also observed from the evolution of the lift coefficient.