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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.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.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.Numerical investigations on transitional flows around forward and reversed hydrofoils
http://hdl.handle.net/10985/21621
Numerical investigations on transitional flows around forward and reversed hydrofoils
SHI, Lei; WANG, Yefang; BAYEUL-LAINE, Annie-Claude; COUTIER-DELGOSHA, Olivier
The laminar-turbulence transition phenomenon widely exists on the surface of many energy equipment, which is deserved to be studied because of the complex mechanics and some induced undesirable consequences. The goal of present work is to investigate the transitional flows around the forward and reversed hydrofoils at different incidences using the SST gamma-Re teta transition model, with special emphasis on the dynamics of the transition. The effect of inflow turbulence condition is considered initially. Then, the difference between the original SST k-ω model and SST γ-Re teta transition model is analyzed, in terms of the near-wall velocity profiles and flow morphology. Afterwards, the change of the transition with the incidence for the reversed hydrofoil is clarified in detail. The primary results show that the flow separation near the sharp leading edge where the reverse dynamic vortex (RDV) appears makes the contribution to the transition. The size of RDV is much larger than laminar separation bubble (LSB) over the forward hydrofoil and it forms near the leading edge earlier. Moreover, the transition locations are mapped both for the forward and reversed hydrofoils. Finally, the effect of Reynolds number on the transition process for the reversed hydrofoil is presented. It is believed that this work can deep the understandings of the transition, especially for the reversed hydrofoils.
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/10985/216212021-01-01T00:00:00ZSHI, LeiWANG, YefangBAYEUL-LAINE, Annie-ClaudeCOUTIER-DELGOSHA, OlivierThe laminar-turbulence transition phenomenon widely exists on the surface of many energy equipment, which is deserved to be studied because of the complex mechanics and some induced undesirable consequences. The goal of present work is to investigate the transitional flows around the forward and reversed hydrofoils at different incidences using the SST gamma-Re teta transition model, with special emphasis on the dynamics of the transition. The effect of inflow turbulence condition is considered initially. Then, the difference between the original SST k-ω model and SST γ-Re teta transition model is analyzed, in terms of the near-wall velocity profiles and flow morphology. Afterwards, the change of the transition with the incidence for the reversed hydrofoil is clarified in detail. The primary results show that the flow separation near the sharp leading edge where the reverse dynamic vortex (RDV) appears makes the contribution to the transition. The size of RDV is much larger than laminar separation bubble (LSB) over the forward hydrofoil and it forms near the leading edge earlier. Moreover, the transition locations are mapped both for the forward and reversed hydrofoils. Finally, the effect of Reynolds number on the transition process for the reversed hydrofoil is presented. It is believed that this work can deep the understandings of the transition, especially for the reversed hydrofoils.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.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.