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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Wed, 13 Nov 2024 22:11:32 GMT2024-11-13T22:11:32ZNumerical 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; COUTIER-DELGOSHA, Olivier; BAYEUL-LAINÉ, Annie-Claude
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, YefangCOUTIER-DELGOSHA, OlivierBAYEUL-LAINÉ, Annie-ClaudeThe 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.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; COUTIER-DELGOSHA, Olivier; BAYEUL-LAINÉ, Annie-Claude
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, YefangCOUTIER-DELGOSHA, OlivierBAYEUL-LAINÉ, Annie-ClaudeThe goal of the present work deals with the influence of the oscillating freestream on the global performance, transition and vortex dynamics of forward and reversed airfoils. Three important parameters, involving the phase lag, oscillating amplitude and mean reduced frequency, are analyzed systematically. The primary results show that both the phase lag and oscillating amplitude have great impact on the transition and flow structures, depending on the instantaneous freestream Reynolds number. The reversed airfoil is more prone to being affected by these parameters, characterized by the earlier flow separation near the sharp leading edge and the more complex vortex shedding, compared with that over the forward airfoil. It shows that increasing the oscillating amplitude can improve the mean performance, but it decreases with the increase of the mean reduced frequency. Additionally, it is observed that there is a second transition on both two sides near the trailing edge of the reversed airfoil, which becomes weak when the instantaneous freestream Reynolds number is relatively low. Afterwards, the time-averaged performance of the reversed airfoil is better than forward airfoil at low reduced frequency, but it deteriorates dramatically with the increase of the reduced frequency. Furthermore, the transition and vortex evolution are delayed as the reduced frequency increases, and the delayed flow structures can be inferred from the velocity profiles in the wake region. Moreover, it can be seen that the velocity profile has a transition from the drag-indicative to thrust-indicative type when the reduced frequency increases, and the velocity variation in the vertical direction is more evident for the reversed airfoil due to the massive flow separation.Investigations 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.