Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind from random direction and easy installation and maintenance. But its aerodynamic performance is very complicated,especia...Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind from random direction and easy installation and maintenance. But its aerodynamic performance is very complicated,especially for the existence of dynamic stall. How to get better aerodynamic performance arouses lots of interests in the design procedure of a straight Darrieus wind turbine. In this paper,mainly the effects of number of blades and tip speed ratio are discussed. Based on the numerical investigation,an assumed asymmetric straight Darrieus wind turbine is proposed to improve the averaged power coefficient. As to the numerical method,the flow around the turbine is simulated by solving the 2D unsteady Navier-Stokes equation combined with continuous equation. The time marching method on a body-fitted coordinate system based on MAC (Marker-and-Cell) method is used. O-type grid is generated for the whole calculation domain. The characteristics of tangential and normal force are discussed related with dynamic stall of the blade. Averaged power coefficient per period of rotating is calculated to evaluate the eligibility of the turbine.展开更多
Wind energy witnessed tremendous growth in the past decade and emerged as the most sought renewable energy source after solar energy. Though the Horizontal Axis Wind Turbines (HAWT) is preferred for multi-megawatt pow...Wind energy witnessed tremendous growth in the past decade and emerged as the most sought renewable energy source after solar energy. Though the Horizontal Axis Wind Turbines (HAWT) is preferred for multi-megawatt power generation, Vertical Axis Wind Turbines (VAWT) is as competitive as HAWT. The current study aims to summarize the development of VAWT, in particular, Darrieus turbine from the past to the project that is underway. The reason for the technical challenges and past failures are discussed. Various configurations of VAWT have been assessed in terms of reliability, components and low wind speed performance. Innovative concepts and the feasibility to scale up for megawatt electricity generation, especially in offshore environments are investigated. This paper is a modest attempt to highlight the state-of-the-art information on the ongoing developments focusing on decentralized power generation. This review is envisioned as an information hub for the major developments in VAWT and its technical advancements so far.展开更多
Darrieus wind turbines are experiencing a renewed interest for their application in decentralized power generation and urban installation. Much attention and research efforts have been dedicated in the past to develop...Darrieus wind turbines are experiencing a renewed interest for their application in decentralized power generation and urban installation. Much attention and research efforts have been dedicated in the past to develop as an efficient standalone Darrieus turbine. Despite these efforts, these vertical axis turbines are still low in efficiency compared to the horizontal axis counterparts. The current architecture of the turbine and their inherent characteristics limit their application in low wind speed areas as confirmed experimentally and computationally by past research. To enable and extend their operation for weak wind flows, a novel design of Adaptive Darrieus Wind Turbine (ADWT) is proposed. The hybrid Darrieus Savonius rotor with dynamically varying Savonius rotor diameter based on the wind speed enables the turbine to start, efficiently operate and stop the turbine at high winds. As the wake of Savonius rotor has a profound impact on the power performance of the combined rotor, the wake of two buckets Savonius rotor in open and closed configuration is reviewed. The current study aims to develop an analytical model to predict the power coefficient and the influence of other design parameters on the proposed design. The formulated analytical model is coded in python, and the results are obtained for the 10 kW rotor. Parametric analysis on the chord length and the diameter of the closed Savonius rotor is performed in search of an optimized diameter to maximize the annual energy output. Blade torque and the rotor torque are evaluated with respect to azimuthal angle and compared with conventional Darrieus rotor. The computed results show that peak power coefficient of ADWT is 13% lower than the conventional Darrieus rotor at the rated wind speed of 10 m/s.展开更多
Straight-blade Darrieus vertical axis wind turbines are used as medium and small size wind turbine because of higher power output in vertical axis wind turbine (VAWT). In our previous study, the relationship between t...Straight-blade Darrieus vertical axis wind turbines are used as medium and small size wind turbine because of higher power output in vertical axis wind turbine (VAWT). In our previous study, the relationship between the performance and Reynolds number based on airfoil chord length had been investigated by using small-scale test models of lift-type VAWT, and the results showed that the performance of tested wind turbine models with small diameter was clearly lower than that of the large-scale field test machine, and its performance also varies significantly with the blade pitch angle. In this study, we focused on the performance of a small-scale straight-blade Darrieus VAWT, the relationship among the blade airfoil camber direction and the pitch angle, and the performance of the small-scale VAWT was examined experimentally by using a small-scale VAWT test model with Gurney flap which was a small flat plate. Gurney flaps with its height h, as a ratio to the blade chord length c, <em>h/c</em> = 0.036 to 0.055, were attached to the blades of the VAWT test model, in addition, the attaching direction of the Gurney flap on the blade was examined for both inward and outward of the rotor, and the pitch angle was also examined for a range of <span style="white-space:nowrap;">−</span>5 to 10 degrees. These results are discussed comparing with the result of the VAWT without Gurney flap and considering the numerical results for the single blade with/without the Gurney flap. The results showed that the performance of the tested VAWT was reversed between the inward and outward Gurney flaps around a pitch angle of 10 degrees. That is, the inward Gurney flap was superior at a pitch angle of less than 10 degrees, while the outward Gurney flap was effective at a pitch angle of more than 10 degrees. Furthermore, for the tested small-scale VAWT model, the optimum pitch angle was about 5 degrees, and the inward and shorter Gurney flap showed higher power performance of the VAWT under this pitch angle condition.展开更多
Darrieus wind turbines are simple lift based machines with exceptionally high efficiencies in terms of power coefficient compared to similar drag based vertical axis turbines. However, in low Reynolds numbers, a notab...Darrieus wind turbines are simple lift based machines with exceptionally high efficiencies in terms of power coefficient compared to similar drag based vertical axis turbines. However, in low Reynolds numbers, a notable performance loss was reported. As a potential solution, truncated NACA 0018 airfoil (NACA 0018TC-39) has been introduced with baseline cavity modification to achieve better start-up characteristics and to enhance the low wind speed performance. The baseline cavity will provide an additional benefit of reverse drag at low TSR which is obligatory for low wind speed start-up. Numerical optimization has been carried out on the conceived airfoil NACA 0018TC-39 to find out the effective truncation percentage in terms of the chord. The numerical study has been extended to compare NACA 0018 and NACA 0018TC-39 airfoil for their aerodynamic performances in terms of lift, drag coefficients and separation characteristics. The NACA 0018TC-39 airfoil was incorporated within a non-swept straight bladed Darrieus turbine miniature to experimentally evaluate the performance in terms of dynamic power coefficient, dynamic torque coefficient and static torque coefficient and compared with conventional NACA 0018 airfoil at six different Reynolds numbers 178917, 193827, 208737, 223646, 238556 and 268376. The experimental contrast implied that NACA 0018TC-39 airfoil turbine yielded almost double power coefficients at low Reynolds number compared to conventional NACA 0018 airfoil without hampering its performance at higher Reynolds number.展开更多
文摘Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind from random direction and easy installation and maintenance. But its aerodynamic performance is very complicated,especially for the existence of dynamic stall. How to get better aerodynamic performance arouses lots of interests in the design procedure of a straight Darrieus wind turbine. In this paper,mainly the effects of number of blades and tip speed ratio are discussed. Based on the numerical investigation,an assumed asymmetric straight Darrieus wind turbine is proposed to improve the averaged power coefficient. As to the numerical method,the flow around the turbine is simulated by solving the 2D unsteady Navier-Stokes equation combined with continuous equation. The time marching method on a body-fitted coordinate system based on MAC (Marker-and-Cell) method is used. O-type grid is generated for the whole calculation domain. The characteristics of tangential and normal force are discussed related with dynamic stall of the blade. Averaged power coefficient per period of rotating is calculated to evaluate the eligibility of the turbine.
文摘Wind energy witnessed tremendous growth in the past decade and emerged as the most sought renewable energy source after solar energy. Though the Horizontal Axis Wind Turbines (HAWT) is preferred for multi-megawatt power generation, Vertical Axis Wind Turbines (VAWT) is as competitive as HAWT. The current study aims to summarize the development of VAWT, in particular, Darrieus turbine from the past to the project that is underway. The reason for the technical challenges and past failures are discussed. Various configurations of VAWT have been assessed in terms of reliability, components and low wind speed performance. Innovative concepts and the feasibility to scale up for megawatt electricity generation, especially in offshore environments are investigated. This paper is a modest attempt to highlight the state-of-the-art information on the ongoing developments focusing on decentralized power generation. This review is envisioned as an information hub for the major developments in VAWT and its technical advancements so far.
文摘Darrieus wind turbines are experiencing a renewed interest for their application in decentralized power generation and urban installation. Much attention and research efforts have been dedicated in the past to develop as an efficient standalone Darrieus turbine. Despite these efforts, these vertical axis turbines are still low in efficiency compared to the horizontal axis counterparts. The current architecture of the turbine and their inherent characteristics limit their application in low wind speed areas as confirmed experimentally and computationally by past research. To enable and extend their operation for weak wind flows, a novel design of Adaptive Darrieus Wind Turbine (ADWT) is proposed. The hybrid Darrieus Savonius rotor with dynamically varying Savonius rotor diameter based on the wind speed enables the turbine to start, efficiently operate and stop the turbine at high winds. As the wake of Savonius rotor has a profound impact on the power performance of the combined rotor, the wake of two buckets Savonius rotor in open and closed configuration is reviewed. The current study aims to develop an analytical model to predict the power coefficient and the influence of other design parameters on the proposed design. The formulated analytical model is coded in python, and the results are obtained for the 10 kW rotor. Parametric analysis on the chord length and the diameter of the closed Savonius rotor is performed in search of an optimized diameter to maximize the annual energy output. Blade torque and the rotor torque are evaluated with respect to azimuthal angle and compared with conventional Darrieus rotor. The computed results show that peak power coefficient of ADWT is 13% lower than the conventional Darrieus rotor at the rated wind speed of 10 m/s.
文摘Straight-blade Darrieus vertical axis wind turbines are used as medium and small size wind turbine because of higher power output in vertical axis wind turbine (VAWT). In our previous study, the relationship between the performance and Reynolds number based on airfoil chord length had been investigated by using small-scale test models of lift-type VAWT, and the results showed that the performance of tested wind turbine models with small diameter was clearly lower than that of the large-scale field test machine, and its performance also varies significantly with the blade pitch angle. In this study, we focused on the performance of a small-scale straight-blade Darrieus VAWT, the relationship among the blade airfoil camber direction and the pitch angle, and the performance of the small-scale VAWT was examined experimentally by using a small-scale VAWT test model with Gurney flap which was a small flat plate. Gurney flaps with its height h, as a ratio to the blade chord length c, <em>h/c</em> = 0.036 to 0.055, were attached to the blades of the VAWT test model, in addition, the attaching direction of the Gurney flap on the blade was examined for both inward and outward of the rotor, and the pitch angle was also examined for a range of <span style="white-space:nowrap;">−</span>5 to 10 degrees. These results are discussed comparing with the result of the VAWT without Gurney flap and considering the numerical results for the single blade with/without the Gurney flap. The results showed that the performance of the tested VAWT was reversed between the inward and outward Gurney flaps around a pitch angle of 10 degrees. That is, the inward Gurney flap was superior at a pitch angle of less than 10 degrees, while the outward Gurney flap was effective at a pitch angle of more than 10 degrees. Furthermore, for the tested small-scale VAWT model, the optimum pitch angle was about 5 degrees, and the inward and shorter Gurney flap showed higher power performance of the VAWT under this pitch angle condition.
文摘Darrieus wind turbines are simple lift based machines with exceptionally high efficiencies in terms of power coefficient compared to similar drag based vertical axis turbines. However, in low Reynolds numbers, a notable performance loss was reported. As a potential solution, truncated NACA 0018 airfoil (NACA 0018TC-39) has been introduced with baseline cavity modification to achieve better start-up characteristics and to enhance the low wind speed performance. The baseline cavity will provide an additional benefit of reverse drag at low TSR which is obligatory for low wind speed start-up. Numerical optimization has been carried out on the conceived airfoil NACA 0018TC-39 to find out the effective truncation percentage in terms of the chord. The numerical study has been extended to compare NACA 0018 and NACA 0018TC-39 airfoil for their aerodynamic performances in terms of lift, drag coefficients and separation characteristics. The NACA 0018TC-39 airfoil was incorporated within a non-swept straight bladed Darrieus turbine miniature to experimentally evaluate the performance in terms of dynamic power coefficient, dynamic torque coefficient and static torque coefficient and compared with conventional NACA 0018 airfoil at six different Reynolds numbers 178917, 193827, 208737, 223646, 238556 and 268376. The experimental contrast implied that NACA 0018TC-39 airfoil turbine yielded almost double power coefficients at low Reynolds number compared to conventional NACA 0018 airfoil without hampering its performance at higher Reynolds number.
