SAM
https://sam.ensam.eu:443
The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Thu, 13 Jun 2024 16:22:17 GMT2024-06-13T16:22:17ZInvestigations 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.Parametrical 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.Experimental investigation of three-dimensional effects in cavitating flows with time-resolved stereo Particle Image Velocimetry Physics of Fluids
http://hdl.handle.net/10985/23284
Experimental investigation of three-dimensional effects in cavitating flows with time-resolved stereo Particle Image Velocimetry Physics of Fluids
LONG, Kunpeng; COUTIER-DELGOSHA, Olivier; BAYEUL-LAINÉ, Annie-Claude
The present paper is devoted to characterizing the three-dimensional effects in a cavitating flow generated in a Venturi-type profile. Experimental measurements based on 2D3C(Two-dimensionalthree-component) stereoscopic PIV(Particle Image Velocimetry) are conducted to obtain the three components of the velocity field in multiple vertical planes aligned with the main flow direction, from the center of the channel to the side walls. Time-resolved acquisitions are conducted, so not only
time-averaged quantities but also velocity fluctuations can be discussed. The attention was focused on configurations of cloud cavitation, where the attached cavity experiences large-scale periodical oscillations and shedding of clouds of vapor. Although the water channel is purely two-dimensional, some significant flow velocities in the third direction (depth of the test section) were measured. Some of those velocities were found to be related to small differences between the boundary conditions on the two sides, such as minor gaps between the sides and the bottom wall, while others reflect intrinsic three-dimensional mechanisms inside the cavitation area, such as side jets that contribute to the periodical instability process. These mechanisms are discussed, and a possible 3D(Threedimensional) structure of the cavitating flow is proposed.
Wed, 01 Feb 2023 00:00:00 GMThttp://hdl.handle.net/10985/232842023-02-01T00:00:00ZLONG, KunpengCOUTIER-DELGOSHA, OlivierBAYEUL-LAINÉ, Annie-ClaudeThe present paper is devoted to characterizing the three-dimensional effects in a cavitating flow generated in a Venturi-type profile. Experimental measurements based on 2D3C(Two-dimensionalthree-component) stereoscopic PIV(Particle Image Velocimetry) are conducted to obtain the three components of the velocity field in multiple vertical planes aligned with the main flow direction, from the center of the channel to the side walls. Time-resolved acquisitions are conducted, so not only
time-averaged quantities but also velocity fluctuations can be discussed. The attention was focused on configurations of cloud cavitation, where the attached cavity experiences large-scale periodical oscillations and shedding of clouds of vapor. Although the water channel is purely two-dimensional, some significant flow velocities in the third direction (depth of the test section) were measured. Some of those velocities were found to be related to small differences between the boundary conditions on the two sides, such as minor gaps between the sides and the bottom wall, while others reflect intrinsic three-dimensional mechanisms inside the cavitation area, such as side jets that contribute to the periodical instability process. These mechanisms are discussed, and a possible 3D(Threedimensional) structure of the cavitating flow is proposed.Effect of pitching angle, pitch-pivot-point, blade camber and deflected sharp leading edge on performance and vortical flows of reversed pitching airfoils
http://hdl.handle.net/10985/23801
Effect of pitching angle, pitch-pivot-point, blade camber and deflected sharp leading edge on performance and vortical flows of reversed pitching airfoils
SHI, Lei; ZHANG, Desheng; BAYEUL-LAINÉ, Annie-Claude; COUTIER-DELGOSHA, Olivier
The goal of the present work is to investigate the influence of several parameters on the performance and flow structures of reversed pitching airfoils. Firstly, the effect of the turbulence model is evaluated, and the results show that the SST
transition model has a better prediction in the instantaneous lift coefficient of a reversed pitching airfoil and the transition locations of a stationary airfoil. Then, effects of the pitching angle, pitch-pivot-point, blade profile and morphed leading edge with various deflection angles and positions on the performance, unsteady vortical flow, near-wall transition and trajectory of main vortices, are analyzed. The main results show that both the mean pitching angle and pitching amplitude have the impact on the vortical flows, but depends on the reduced frequency. Then, the delayed flow structure by shifting the pitch-pivot-point from the leading edge (LE) to trailing edge (TE) can be explained by the distribution of the effective attack-of-angle. Moreover, the symmetrical, asymmetrical and inverse asymmetrical airfoils have great effect on the first (FMLC) and second maximal lift coefficients (SMLC). Finally, upward deflected LE decreases the negative lift coefficient while downward morphed LE improves it considerably due to the geometry curvature leading to the large flow separation. In addition, it is observed that the generation of vortices is earlier when the deflection position close to the middle surface. It is believed that this work can provide some guidelines to have a better design of energy devices with oscillating airfoils/hydrofoils.
Sat, 01 Jul 2023 00:00:00 GMThttp://hdl.handle.net/10985/238012023-07-01T00:00:00ZSHI, LeiZHANG, DeshengBAYEUL-LAINÉ, Annie-ClaudeCOUTIER-DELGOSHA, OlivierThe goal of the present work is to investigate the influence of several parameters on the performance and flow structures of reversed pitching airfoils. Firstly, the effect of the turbulence model is evaluated, and the results show that the SST
transition model has a better prediction in the instantaneous lift coefficient of a reversed pitching airfoil and the transition locations of a stationary airfoil. Then, effects of the pitching angle, pitch-pivot-point, blade profile and morphed leading edge with various deflection angles and positions on the performance, unsteady vortical flow, near-wall transition and trajectory of main vortices, are analyzed. The main results show that both the mean pitching angle and pitching amplitude have the impact on the vortical flows, but depends on the reduced frequency. Then, the delayed flow structure by shifting the pitch-pivot-point from the leading edge (LE) to trailing edge (TE) can be explained by the distribution of the effective attack-of-angle. Moreover, the symmetrical, asymmetrical and inverse asymmetrical airfoils have great effect on the first (FMLC) and second maximal lift coefficients (SMLC). Finally, upward deflected LE decreases the negative lift coefficient while downward morphed LE improves it considerably due to the geometry curvature leading to the large flow separation. In addition, it is observed that the generation of vortices is earlier when the deflection position close to the middle surface. It is believed that this work can provide some guidelines to have a better design of energy devices with oscillating airfoils/hydrofoils.Analysis of performance and flow structures of cycloidal rotors under different pitch-pivot-point and blade camber conditions
http://hdl.handle.net/10985/24221
Analysis of performance and flow structures of cycloidal rotors under different pitch-pivot-point and blade camber conditions
SHI, Lei; ZHANG, Desheng; BAYEUL-LAINÉ, Annie-Claude; COUTIER-DELGOSHA, Olivier
The performance and unsteady vortical flows of a 2-bladed cycloidal propeller are investigated using the SST γ ��
Reθt transition model, under different pitch-pivot-point and blade camber conditions. Firstly, it shows that the results of the present computations match well with the previous numerical data and experiments, in terms of the instantaneous performance and internal flow structures. Then, due to the moderate propulsive force and low power, the cycloidal rotor with a pitch-pivot-point of x/c = 0.25 maximize the efficiency. Moving the pitching location to the leading edge increases the lift and leads to the earlier flow separation on the blade surface. However, as the pitch-pivot-point shifts to the middle chord, the power of the cycloidal rotor increases dramatically because of the massive flow separation, leading to the degradation of the performance. Simultaneously,
the symmetrical profiles, involving NACA0012 and 0015, are recommended due to the wide operation condition with high efficiency. The thick symmetrical and asymmetrical airfoils produce the worst performance due to the large power that is consumed. Furthermore, owing to the change of the rotating speed only, the advance coefficient effect is more obvious than the Reynolds number. When analyzing the performance of the rotating system at any position, one should consider the performance, pressure difference, near-wall flows and forces (lift and drag) of each blade.
Wed, 01 Nov 2023 00:00:00 GMThttp://hdl.handle.net/10985/242212023-11-01T00:00:00ZSHI, LeiZHANG, DeshengBAYEUL-LAINÉ, Annie-ClaudeCOUTIER-DELGOSHA, OlivierThe performance and unsteady vortical flows of a 2-bladed cycloidal propeller are investigated using the SST γ ��
Reθt transition model, under different pitch-pivot-point and blade camber conditions. Firstly, it shows that the results of the present computations match well with the previous numerical data and experiments, in terms of the instantaneous performance and internal flow structures. Then, due to the moderate propulsive force and low power, the cycloidal rotor with a pitch-pivot-point of x/c = 0.25 maximize the efficiency. Moving the pitching location to the leading edge increases the lift and leads to the earlier flow separation on the blade surface. However, as the pitch-pivot-point shifts to the middle chord, the power of the cycloidal rotor increases dramatically because of the massive flow separation, leading to the degradation of the performance. Simultaneously,
the symmetrical profiles, involving NACA0012 and 0015, are recommended due to the wide operation condition with high efficiency. The thick symmetrical and asymmetrical airfoils produce the worst performance due to the large power that is consumed. Furthermore, owing to the change of the rotating speed only, the advance coefficient effect is more obvious than the Reynolds number. When analyzing the performance of the rotating system at any position, one should consider the performance, pressure difference, near-wall flows and forces (lift and drag) of each blade.Analysis of high-speed drop impact onto deep liquid pool
http://hdl.handle.net/10985/24301
Analysis of high-speed drop impact onto deep liquid pool
WANG, Hui; LIU, Shuo; BAYEUL-LAINÉ, Annie-Claude; MURPHY, David; KATZ, Joseph; COUTIER-DELGOSHA, Olivier
The present work is devoted to the analysis of drop impact on a deep liquid pool, focusing on the high-energy splashing regimes caused by large raindrops at high velocities. Such cases are characterized by short time scales and complex mechanisms, thus they have received very little attention until now. The BASILISK open-source solver is used to perform three-dimensional direct numerical simulations. The capabilities of octree adaptive mesh refinement techniques enable capturing of the small-scale features of the flow, while the volume of fluid approach combined with a balanced-force surface-tension calculation is applied to advect the volume fraction of the liquids and reconstruct the interfaces. The numerical results compare well with experimental visualizations: both the evolution of crown and cavity, the emanation of ligaments, the formation of bubble canopy and the growth of a downward-moving spiral jet that pierces through the cavity bottom, are correctly reproduced. Reliable quantitative agreements are also obtained regarding the time evolution of rim positions, cavity dimensions and droplet distributions through an observation window. Furthermore, simulation gives access to various aspects of the internal flows, which allows us to better explain the observed physical phenomena. Details of the early-time dynamics of bubble ring entrapment and splashing performance, the formation/collapse of bubble canopy and the spreading of drop liquid are discussed. The statistics of droplet size show the bimodal distribution in time, corroborating distinct primary mechanisms of droplet production at different stages.
Sun, 01 Oct 2023 00:00:00 GMThttp://hdl.handle.net/10985/243012023-10-01T00:00:00ZWANG, HuiLIU, ShuoBAYEUL-LAINÉ, Annie-ClaudeMURPHY, DavidKATZ, JosephCOUTIER-DELGOSHA, OlivierThe present work is devoted to the analysis of drop impact on a deep liquid pool, focusing on the high-energy splashing regimes caused by large raindrops at high velocities. Such cases are characterized by short time scales and complex mechanisms, thus they have received very little attention until now. The BASILISK open-source solver is used to perform three-dimensional direct numerical simulations. The capabilities of octree adaptive mesh refinement techniques enable capturing of the small-scale features of the flow, while the volume of fluid approach combined with a balanced-force surface-tension calculation is applied to advect the volume fraction of the liquids and reconstruct the interfaces. The numerical results compare well with experimental visualizations: both the evolution of crown and cavity, the emanation of ligaments, the formation of bubble canopy and the growth of a downward-moving spiral jet that pierces through the cavity bottom, are correctly reproduced. Reliable quantitative agreements are also obtained regarding the time evolution of rim positions, cavity dimensions and droplet distributions through an observation window. Furthermore, simulation gives access to various aspects of the internal flows, which allows us to better explain the observed physical phenomena. Details of the early-time dynamics of bubble ring entrapment and splashing performance, the formation/collapse of bubble canopy and the spreading of drop liquid are discussed. The statistics of droplet size show the bimodal distribution in time, corroborating distinct primary mechanisms of droplet production at different stages.Wave statistics and energy dissipation of shallow-water breaking waves in a tank with a level bottom
http://hdl.handle.net/10985/24761
Wave statistics and energy dissipation of shallow-water breaking waves in a tank with a level bottom
LIU, Shuo; WANG, Hui; BAYEUL-LAINÉ, Annie-Claude; LI, Cheng; KATZ, Joseph; COUTIER-DELGOSHA, Olivier
The present study focuses on two-dimensional direct numerical simulations of shallow-water breaking waves, specifically those generated by a wave plate at constant water depths. The primary objective is to quantitatively analyse the dynamics, kinematics and energy dissipation associated with wave breaking. The numerical results exhibit good agreement with experimental data in terms of free-surface profiles during wave breaking. A parametric study was conducted to examine the influence of various wave properties and initial conditions on breaking characteristics. According to research on the Bond number (
$Bo$
, the ratio of gravitational to surface tension forces), an increased surface tension leads to the formation of more prominent parasitic capillaries at the forwards face of the wave profile and a thicker plunging jet, which causes a delayed breaking time and is tightly correlated with the main cavity size. A close relationship between wave statistics and the initial conditions of the wave plate is discovered, allowing for the classification of breaker types based on the ratio of wave height to water depth,
$H/d$
. Moreover, an analysis based on inertial scaling arguments reveals that the energy dissipation rate due to breaking can be linked to the local geometry of the breaking crest
$H_b/d$
, and exhibits a threshold behaviour, where the energy dissipation approaches zero at a critical value of
$H_b/d$
. An empirical scaling of the breaking parameter is proposed as
$b = a(H_b/d - \chi _0)^n$
, where
$\chi _0 = 0.65$
represents the breaking threshold and
$n = 1.5$
is a power law determined through the best fit to the numerical results.
Wed, 01 Nov 2023 00:00:00 GMThttp://hdl.handle.net/10985/247612023-11-01T00:00:00ZLIU, ShuoWANG, HuiBAYEUL-LAINÉ, Annie-ClaudeLI, ChengKATZ, JosephCOUTIER-DELGOSHA, OlivierThe present study focuses on two-dimensional direct numerical simulations of shallow-water breaking waves, specifically those generated by a wave plate at constant water depths. The primary objective is to quantitatively analyse the dynamics, kinematics and energy dissipation associated with wave breaking. The numerical results exhibit good agreement with experimental data in terms of free-surface profiles during wave breaking. A parametric study was conducted to examine the influence of various wave properties and initial conditions on breaking characteristics. According to research on the Bond number (
$Bo$
, the ratio of gravitational to surface tension forces), an increased surface tension leads to the formation of more prominent parasitic capillaries at the forwards face of the wave profile and a thicker plunging jet, which causes a delayed breaking time and is tightly correlated with the main cavity size. A close relationship between wave statistics and the initial conditions of the wave plate is discovered, allowing for the classification of breaker types based on the ratio of wave height to water depth,
$H/d$
. Moreover, an analysis based on inertial scaling arguments reveals that the energy dissipation rate due to breaking can be linked to the local geometry of the breaking crest
$H_b/d$
, and exhibits a threshold behaviour, where the energy dissipation approaches zero at a critical value of
$H_b/d$
. An empirical scaling of the breaking parameter is proposed as
$b = a(H_b/d - \chi _0)^n$
, where
$\chi _0 = 0.65$
represents the breaking threshold and
$n = 1.5$
is a power law determined through the best fit to the numerical results.Effect of time-varying freestream on performance and vortex dynamics of forward and reversed pitching airfoils
http://hdl.handle.net/10985/21620
Effect of time-varying freestream on performance and vortex dynamics of forward and reversed pitching airfoils
SHI, Lei; WANG, Yefang; BAYEUL-LAINE, Annie-Claude; COUTIER-DELGOSHA, Olivier
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.
Sat, 01 Jan 2022 00:00:00 GMThttp://hdl.handle.net/10985/216202022-01-01T00:00:00ZSHI, LeiWANG, YefangBAYEUL-LAINE, Annie-ClaudeCOUTIER-DELGOSHA, OlivierThe 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.Direct Numerical Simulation of Shallow Water Breaking Waves Generated by Wave Plate
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.Effects of Non-Sinusoidal Motion and Effective Angle of Attack on Energy Extraction Performance of a Fully- Activated Flapping Foil
http://hdl.handle.net/10985/20265
Effects of Non-Sinusoidal Motion and Effective Angle of Attack on Energy Extraction Performance of a Fully- Activated Flapping Foil
BOUDIS, A.; OUALLI, H.; BENZAOUI, A.; GUERRI, O; BAYEUL-LAINE, Annie-Claude; COUTIER-DELGOSHA, Olivier
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 finite-volume 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 f = 90 , a reduced frequency f = 0:14, and an effective angle of attack amax varying between 15 and 50 , corresponding to a pitching amplitude in the range q0 = 55:51 to 90:51 . The results show that, the non-sinusoidal trajectory affects considerably the energy extraction performances. For the reference case (sinusoidal heaving and pitching motions, Sh = Sq = 1), best performances are obtained for the effective angle of attack, amax = 40 . At small effective angle of attack amax < 30 , the non-sinusoidal pitching motion combined with a sinusoidal heaving motion, greatly improve energy extraction performances. For amax = 15 , Sh = 1 and Sq = 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 ( amax >40 ), non-sinusoidal pitching motion has a negative effect. Performance improvement is quite limited with the combined motions non-sinusoidal heaving/sinusoidal pitching.
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/10985/202652021-01-01T00:00:00ZBOUDIS, A.OUALLI, H.BENZAOUI, A.GUERRI, OBAYEUL-LAINE, Annie-ClaudeCOUTIER-DELGOSHA, OlivierFlapping 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 finite-volume 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 f = 90 , a reduced frequency f = 0:14, and an effective angle of attack amax varying between 15 and 50 , corresponding to a pitching amplitude in the range q0 = 55:51 to 90:51 . The results show that, the non-sinusoidal trajectory affects considerably the energy extraction performances. For the reference case (sinusoidal heaving and pitching motions, Sh = Sq = 1), best performances are obtained for the effective angle of attack, amax = 40 . At small effective angle of attack amax < 30 , the non-sinusoidal pitching motion combined with a sinusoidal heaving motion, greatly improve energy extraction performances. For amax = 15 , Sh = 1 and Sq = 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 ( amax >40 ), non-sinusoidal pitching motion has a negative effect. Performance improvement is quite limited with the combined motions non-sinusoidal heaving/sinusoidal pitching.