Vertical-axis wind turbines(VAWTs)are receiving growing interest in offshore wind energy exploitation.However,they often exhibit suboptimal energy conversion efficiency,particularly at low tip speed ratios(TSRs).One c...Vertical-axis wind turbines(VAWTs)are receiving growing interest in offshore wind energy exploitation.However,they often exhibit suboptimal energy conversion efficiency,particularly at low tip speed ratios(TSRs).One critical challenge is suppressing flow separation and dynamic stall on the blades.Passive flow control techniques have shown potential in improving blade aerodynamics,yet a simple and effective approach is still desired.This study proposes a novel leading-edge slot structure aimed at enhancing the power efficiency of VAWTs without additional energy input.The structure facilitates natural suction and blowing flows on the suction side of the blades.High-fidelity computational fluid dynamics simulations incorporating a transition shear stress transport model are employed to examine turbine aerodynamics.The power performance and aerodynamic loads of VAWTs with various slotted blade designs(different start locations,0.02c≤x_(Ⅰ)≤0.31c,and end locations,0.1c≤x_(Ⅱ)≤0.35c,where c denotes the blade chord length)are compared to identify the relatively optimal slot configuration.The analysis of blade boundary layer phenomena and flow state in the slot further elucidates the flow control mechanism.Results indicate that the leading-edge slot structure significantly enhances the power efficiency of the VAWT at low TSRs.The relatively optimal slot configuration(x_(Ⅰ)=0.16c,x_(Ⅱ)=0.2c)yields an average power increase of 38.33% under studied operating conditions.Laminar separation bubble bursting is delayed or even eliminated for slotted blades at low and moderate TSRs.The leading-edge slot structure also delays trailing-edge separation,suppresses dynamic stall vortex formation,and reduces shedding vortex strength,thereby increasing the blade lift-to-drag ratio.This study would facilitate the blade design of VAWTs.展开更多
Quasi-periodical evolutions such as shedding and collapsing of unsteady cloud cavitating flow, induce strong pressure fluctuations, what may deteriorate maneuvering stability and corrode surfaces of underwater vehicle...Quasi-periodical evolutions such as shedding and collapsing of unsteady cloud cavitating flow, induce strong pressure fluctuations, what may deteriorate maneuvering stability and corrode surfaces of underwater vehicles. This paper analyzed effects on cavitation stability of a trip bar arranged on high-speed underwater projectile. Small scale water tank experiment and large eddy simulation using the open source software Open FOAM were used, and the results agree well with each other. Results also indicate that trip bar can obstruct downstream re-entrant jet and pressure wave propagation caused by collapse, resulting in a relatively stable sheet cavity between trip bar and shoulder of projectiles.展开更多
Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to app...Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to appraise the practicability of weakening shock waves and, hence, reducing the wave drag in transonic flight regime using a two-dimensional jagged wall and thereby to gain an appropriate jagged wall shape for future empirical study. Different shapes of the jagged wall, including rectangular, circular, and triangular shapes, were employed. The numerical method was validated by experimental and numerical studies involving transonic flow over the NACA0012 airfoil, and the results presented here closely match previous experimental and numerical results. The impact of parameters, including shape and the length-to-spacing ratio of a jagged wall, was studied on aerodynamic forces and flow field. The results revealed that applying a jagged wall method on the upper surface of an airfoil changes the shock structure significantly and disintegrates it, which in turn leads to a decrease in wave drag. It was also found that the maximum drag coefficient decrease of around 17 % occurs with a triangular shape, while the maximum increase in aerodynamic efficiency（lift-to-drag ratio）of around 10 % happens with a rectangular shape at an angle of attack of 2.26？.展开更多
The stability of high-speed trains under crosswind conditions has become a key consideration in aerodynamic design.As running speeds continue to increase and car body weight decreases,crosswinds pose a greater risk to...The stability of high-speed trains under crosswind conditions has become a key consideration in aerodynamic design.As running speeds continue to increase and car body weight decreases,crosswinds pose a greater risk to train safety,significantly lowering the critical wind velocity.Therefore,developing strategies to enhance crosswind stability is essential.This study focuses on the leeward region adjacent to the train body,where separated flows with large vortices generate significant negative surface pressure.Enhancing this negative pressure distribution is proposed as a potential method to improve a train’s resistance to overturning.To achieve this,winglets are installed on the leeward side as a flow control measure,and their effects at different deflection angles are evaluated.The influence of five deflection angles on the leeward-side flow field and aerodynamic loads is analyzed,considering the head,middle,and tail cars.Results indicate that a deflection angle of 90°optimally reduces the overall overturning moment by 27.6%compared to the baseline model in a three-car configuration.These findings highlight that optimizing the winglet deflection angle to approximately 90°can significantly enhance a train’s resistance to overturning,offering valuable insights for aerodynamic optimization in strong wind conditions.展开更多
Biomimetics has recently emerged as an interesting approach to enhance renewable energy technologies.In this work,bioinspired Trailing Edge Serrations(TES)were evaluated on a typical Vertical Axis Wind Turbine(VAWT)ai...Biomimetics has recently emerged as an interesting approach to enhance renewable energy technologies.In this work,bioinspired Trailing Edge Serrations(TES)were evaluated on a typical Vertical Axis Wind Turbine(VAWT)airfoil,the DU06-W200.As noise reduction benefits of these mechanisms are already well-established,this study focuses on their impact on airfoil and VAWT performance.A saw-tooth geometry was chosen based on VAWT specifications and existing research,followed by a detailed assessment through wind tunnel tests using a newly developed aerodynamic balance.For a broad spectrum of attack angles and Reynolds numbers,lift,drag,and pitching moments were carefully measured.The results show that TES enhance the lift-to-drag ratio,especially in stalled conditions,and postpone stall at negative angles,expanding the effective performance range.A notable increase in pitching moment also is also observed,relevant for blade-strut joint design.Additionally,the impact on turbine performance was estimated using an analytical model,demonstrating excellent accuracy when compared against previous experimental results.TES offer a modest 2%improve-ment in peak performance,though they slightly narrow the optimal tip-speed ratio zone.Despite this,the potential noise reduction and performance gains make TES a valuable addition to VAWT designs,especially in urban settings.展开更多
Transonic internal flow around an airfoil is associated with self-excited unsteady shock wave oscillation. This unsteady phenomenon generates buffet, high speed impulsive noise, non-synchronous vibration, high cycle f...Transonic internal flow around an airfoil is associated with self-excited unsteady shock wave oscillation. This unsteady phenomenon generates buffet, high speed impulsive noise, non-synchronous vibration, high cycle fatigue failure and so on. Present study investigates the effectiveness of perforated cavity to control this unsteady flow field. The cavity has been incorporated on the airfoil surface. The degree of perforation of the cavity is kept constant as 30%. However, the number of openings(perforation) at the cavity upper wall has been varied. Results showed that this passive control reduces the strength of shock wave compared to that of baseline airfoil. As a result, the intensity of shock wave/boundary layer interaction and the root mean square(RMS) of pressure oscillation around the airfoil have been reduced with the control method.展开更多
Gas Turbines are among the most important energy systems for aviation and thermal-based power generation.The performance of gas turbine intakes with S-shaped diffusers is vulnerable to flow separation,reversal flow,an...Gas Turbines are among the most important energy systems for aviation and thermal-based power generation.The performance of gas turbine intakes with S-shaped diffusers is vulnerable to flow separation,reversal flow,and pressure distortion,mainly in aggressive S-shaped diffusers.Severalmethods,including vortex generators and energy promoters,have been proposed and investigated both experimentally and numerically.This paper compiles a review of experimental investigations that have been performed and reported to mitigate flow separation and restore system performance.The operational principles,classifications,design geometries,and performance parameters of Sshaped diffusers are presented to facilitate the analysis and understanding of the influence of each mitigation method on flowenhancement in S-shaped diffusers.Theinfluencing design parameters on the performance of the S-shaped diffuser and the findings achieved by various experimental investigations are discussed and compared.The review concludes that reducing the intake length reduces the size and weight of the gas turbine,leading to a higher power-to-weight ratio.However,the main challenge in shortening the S-shaped diffusers is the flow separation in the high-curvature section,which must be prevented to maintain high performance.Prevention can be achieved through flow control methods,which are categorized into passive and aggressive methods.The static pressure recovery coefficient,total pressure loss coefficient,ideal static pressure coefficient,distortion coefficient,and skin friction coefficient are the primary performance evaluation and comparison parameters between the experimentally investigated mitigation methods.The new trend in S-shaped diffuser studies includes the integration of computational and data-driven methods.展开更多
This study investigates the effects of a novel passive flow control mechanism,a flexible leading edge(LE),on the aerodynamic performance of a NACA 0018 airfoil and a scaled vertical axis wind turbine(VAWT)model.Wind t...This study investigates the effects of a novel passive flow control mechanism,a flexible leading edge(LE),on the aerodynamic performance of a NACA 0018 airfoil and a scaled vertical axis wind turbine(VAWT)model.Wind tunnel experiments were conducted on 2D airfoil sections under steady flow and dynamic pitching conditions,and a scaled VAWT model was tested in an open-field environment.The flexible LE airfoil demonstrated significant improvements in delaying static stall angles and enhancing lift generation during dynamic pitching by inducing earlier and prolonged high suction pressures.The scaled VAWT model with flexible LE blades showed increased rotational speeds and higher voltage outputs compared with the rigid blade VAWT,particularly at higher wind speeds.Both rotational speed and electrical voltage data suggest that the flexible LE structure enhances the aerodynamic efficiency of the VAWT.The findings suggest that the flexible LE structure is an efficient and cost-effective method to improve VAWT aerodynamic efficiency.展开更多
Aerodynamic drag is a large resistance force to vehicle motion,particularly at highway speeds.Conventional wheel deflectors were designed to reduce the wheel drag and,consequently,the overall vehicle drag;however,they...Aerodynamic drag is a large resistance force to vehicle motion,particularly at highway speeds.Conventional wheel deflectors were designed to reduce the wheel drag and,consequently,the overall vehicle drag;however,they may actually be detrimental to vehicle aerodynamics in modern designs.In the present study,computational fluid dynamics simulations were conducted on the notchback DrivAer model-a simplified,yet realistic,open-source vehicle model that incorporates features of a modern passenger vehicle.Conventional and air-jet wheel deflectors upstream of the front wheels were introduced to assess the effect of underbody-flow deflection on the vehicle drag.Conventional wheel-deflector designs with varying heights were observed and compared to 45◦and 90◦air-jet wheel deflectors.The conventional wheel deflectors reduced wheel drag but resulted in an overall drag increase of up to 10%.For the cases studied,the 90◦air jet did not reduce the overall drag compared to the baseline case;the 45◦air jet presented drag benefits of up to 1.5%at 35 m/s and above.Compared to conventional wheel deflectors,air-jet wheel deflectors have the potential to reduce vehicle drag to a greater extent and present the benefit of being turned off at lower speeds when flow deflection is undesirable,thus improving efficiency and reducing emissions.展开更多
基金the National Key R&D Program of China(No.2023YFE0120000)Guangdong Basic and Applied Basic Research Foundation(No.2023A1515240054)+1 种基金Program for Intergovernmental International S&T Cooperation Projects of Shanghai Municipality,China(No.24510711100,22160710200)National Natural Science Founda-tion of China(Nos.52122110 and 42076210)are gratefully acknowledged.
文摘Vertical-axis wind turbines(VAWTs)are receiving growing interest in offshore wind energy exploitation.However,they often exhibit suboptimal energy conversion efficiency,particularly at low tip speed ratios(TSRs).One critical challenge is suppressing flow separation and dynamic stall on the blades.Passive flow control techniques have shown potential in improving blade aerodynamics,yet a simple and effective approach is still desired.This study proposes a novel leading-edge slot structure aimed at enhancing the power efficiency of VAWTs without additional energy input.The structure facilitates natural suction and blowing flows on the suction side of the blades.High-fidelity computational fluid dynamics simulations incorporating a transition shear stress transport model are employed to examine turbine aerodynamics.The power performance and aerodynamic loads of VAWTs with various slotted blade designs(different start locations,0.02c≤x_(Ⅰ)≤0.31c,and end locations,0.1c≤x_(Ⅱ)≤0.35c,where c denotes the blade chord length)are compared to identify the relatively optimal slot configuration.The analysis of blade boundary layer phenomena and flow state in the slot further elucidates the flow control mechanism.Results indicate that the leading-edge slot structure significantly enhances the power efficiency of the VAWT at low TSRs.The relatively optimal slot configuration(x_(Ⅰ)=0.16c,x_(Ⅱ)=0.2c)yields an average power increase of 38.33% under studied operating conditions.Laminar separation bubble bursting is delayed or even eliminated for slotted blades at low and moderate TSRs.The leading-edge slot structure also delays trailing-edge separation,suppresses dynamic stall vortex formation,and reduces shedding vortex strength,thereby increasing the blade lift-to-drag ratio.This study would facilitate the blade design of VAWTs.
基金the National Nature Science Foundation of China (11332011 and 11202215)
文摘Quasi-periodical evolutions such as shedding and collapsing of unsteady cloud cavitating flow, induce strong pressure fluctuations, what may deteriorate maneuvering stability and corrode surfaces of underwater vehicles. This paper analyzed effects on cavitation stability of a trip bar arranged on high-speed underwater projectile. Small scale water tank experiment and large eddy simulation using the open source software Open FOAM were used, and the results agree well with each other. Results also indicate that trip bar can obstruct downstream re-entrant jet and pressure wave propagation caused by collapse, resulting in a relatively stable sheet cavity between trip bar and shoulder of projectiles.
文摘Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to appraise the practicability of weakening shock waves and, hence, reducing the wave drag in transonic flight regime using a two-dimensional jagged wall and thereby to gain an appropriate jagged wall shape for future empirical study. Different shapes of the jagged wall, including rectangular, circular, and triangular shapes, were employed. The numerical method was validated by experimental and numerical studies involving transonic flow over the NACA0012 airfoil, and the results presented here closely match previous experimental and numerical results. The impact of parameters, including shape and the length-to-spacing ratio of a jagged wall, was studied on aerodynamic forces and flow field. The results revealed that applying a jagged wall method on the upper surface of an airfoil changes the shock structure significantly and disintegrates it, which in turn leads to a decrease in wave drag. It was also found that the maximum drag coefficient decrease of around 17 % occurs with a triangular shape, while the maximum increase in aerodynamic efficiency（lift-to-drag ratio）of around 10 % happens with a rectangular shape at an angle of attack of 2.26？.
基金Project(2020YFA0710903)supported by the National Key Research and Development Program of ChinaProject(2025ZZTS0623)supported by the Graduate Student Independent Innovation Project of Central South University,ChinaProject(202406370145)supported by the China Scholarship Council。
文摘The stability of high-speed trains under crosswind conditions has become a key consideration in aerodynamic design.As running speeds continue to increase and car body weight decreases,crosswinds pose a greater risk to train safety,significantly lowering the critical wind velocity.Therefore,developing strategies to enhance crosswind stability is essential.This study focuses on the leeward region adjacent to the train body,where separated flows with large vortices generate significant negative surface pressure.Enhancing this negative pressure distribution is proposed as a potential method to improve a train’s resistance to overturning.To achieve this,winglets are installed on the leeward side as a flow control measure,and their effects at different deflection angles are evaluated.The influence of five deflection angles on the leeward-side flow field and aerodynamic loads is analyzed,considering the head,middle,and tail cars.Results indicate that a deflection angle of 90°optimally reduces the overall overturning moment by 27.6%compared to the baseline model in a three-car configuration.These findings highlight that optimizing the winglet deflection angle to approximately 90°can significantly enhance a train’s resistance to overturning,offering valuable insights for aerodynamic optimization in strong wind conditions.
基金The authors wish to thank the financial support of the Spanish Ministry of Science,Innovation and Universities in reference to the Project:Efficiency improvement and noise reduction of a vertical axis wind turbine for urban environments(MERTURB)-Ref.MCINN-22-TED2021-131307B-100.
文摘Biomimetics has recently emerged as an interesting approach to enhance renewable energy technologies.In this work,bioinspired Trailing Edge Serrations(TES)were evaluated on a typical Vertical Axis Wind Turbine(VAWT)airfoil,the DU06-W200.As noise reduction benefits of these mechanisms are already well-established,this study focuses on their impact on airfoil and VAWT performance.A saw-tooth geometry was chosen based on VAWT specifications and existing research,followed by a detailed assessment through wind tunnel tests using a newly developed aerodynamic balance.For a broad spectrum of attack angles and Reynolds numbers,lift,drag,and pitching moments were carefully measured.The results show that TES enhance the lift-to-drag ratio,especially in stalled conditions,and postpone stall at negative angles,expanding the effective performance range.A notable increase in pitching moment also is also observed,relevant for blade-strut joint design.Additionally,the impact on turbine performance was estimated using an analytical model,demonstrating excellent accuracy when compared against previous experimental results.TES offer a modest 2%improve-ment in peak performance,though they slightly narrow the optimal tip-speed ratio zone.Despite this,the potential noise reduction and performance gains make TES a valuable addition to VAWT designs,especially in urban settings.
基金carried out with the computational resource support from sub-project CP 3111 (AIF 3rd round) of Higher Education Quality Enhancement Project (HEQEP), UGC, MoE, GoB
文摘Transonic internal flow around an airfoil is associated with self-excited unsteady shock wave oscillation. This unsteady phenomenon generates buffet, high speed impulsive noise, non-synchronous vibration, high cycle fatigue failure and so on. Present study investigates the effectiveness of perforated cavity to control this unsteady flow field. The cavity has been incorporated on the airfoil surface. The degree of perforation of the cavity is kept constant as 30%. However, the number of openings(perforation) at the cavity upper wall has been varied. Results showed that this passive control reduces the strength of shock wave compared to that of baseline airfoil. As a result, the intensity of shock wave/boundary layer interaction and the root mean square(RMS) of pressure oscillation around the airfoil have been reduced with the control method.
文摘Gas Turbines are among the most important energy systems for aviation and thermal-based power generation.The performance of gas turbine intakes with S-shaped diffusers is vulnerable to flow separation,reversal flow,and pressure distortion,mainly in aggressive S-shaped diffusers.Severalmethods,including vortex generators and energy promoters,have been proposed and investigated both experimentally and numerically.This paper compiles a review of experimental investigations that have been performed and reported to mitigate flow separation and restore system performance.The operational principles,classifications,design geometries,and performance parameters of Sshaped diffusers are presented to facilitate the analysis and understanding of the influence of each mitigation method on flowenhancement in S-shaped diffusers.Theinfluencing design parameters on the performance of the S-shaped diffuser and the findings achieved by various experimental investigations are discussed and compared.The review concludes that reducing the intake length reduces the size and weight of the gas turbine,leading to a higher power-to-weight ratio.However,the main challenge in shortening the S-shaped diffusers is the flow separation in the high-curvature section,which must be prevented to maintain high performance.Prevention can be achieved through flow control methods,which are categorized into passive and aggressive methods.The static pressure recovery coefficient,total pressure loss coefficient,ideal static pressure coefficient,distortion coefficient,and skin friction coefficient are the primary performance evaluation and comparison parameters between the experimentally investigated mitigation methods.The new trend in S-shaped diffuser studies includes the integration of computational and data-driven methods.
文摘This study investigates the effects of a novel passive flow control mechanism,a flexible leading edge(LE),on the aerodynamic performance of a NACA 0018 airfoil and a scaled vertical axis wind turbine(VAWT)model.Wind tunnel experiments were conducted on 2D airfoil sections under steady flow and dynamic pitching conditions,and a scaled VAWT model was tested in an open-field environment.The flexible LE airfoil demonstrated significant improvements in delaying static stall angles and enhancing lift generation during dynamic pitching by inducing earlier and prolonged high suction pressures.The scaled VAWT model with flexible LE blades showed increased rotational speeds and higher voltage outputs compared with the rigid blade VAWT,particularly at higher wind speeds.Both rotational speed and electrical voltage data suggest that the flexible LE structure enhances the aerodynamic efficiency of the VAWT.The findings suggest that the flexible LE structure is an efficient and cost-effective method to improve VAWT aerodynamic efficiency.
文摘Aerodynamic drag is a large resistance force to vehicle motion,particularly at highway speeds.Conventional wheel deflectors were designed to reduce the wheel drag and,consequently,the overall vehicle drag;however,they may actually be detrimental to vehicle aerodynamics in modern designs.In the present study,computational fluid dynamics simulations were conducted on the notchback DrivAer model-a simplified,yet realistic,open-source vehicle model that incorporates features of a modern passenger vehicle.Conventional and air-jet wheel deflectors upstream of the front wheels were introduced to assess the effect of underbody-flow deflection on the vehicle drag.Conventional wheel-deflector designs with varying heights were observed and compared to 45◦and 90◦air-jet wheel deflectors.The conventional wheel deflectors reduced wheel drag but resulted in an overall drag increase of up to 10%.For the cases studied,the 90◦air jet did not reduce the overall drag compared to the baseline case;the 45◦air jet presented drag benefits of up to 1.5%at 35 m/s and above.Compared to conventional wheel deflectors,air-jet wheel deflectors have the potential to reduce vehicle drag to a greater extent and present the benefit of being turned off at lower speeds when flow deflection is undesirable,thus improving efficiency and reducing emissions.
