The Experts below are selected from a list of 42405 Experts worldwide ranked by ideXlab platform

Wei Li - One of the best experts on this subject based on the ideXlab platform.

  • effect of relative camber on the Aerodynamic Performance improvement of asymmetrical blunt trailing edge modification
    Journal of Engineering Thermophysics, 2017
    Co-Authors: Xu Zhang, G G Wang, M.j. Zhang, Wei Li
    Abstract:

    In this paper, the Aerodynamic Performance of the S series of wind turbine airfoils with different relative cambers and their modifications is numerically studied to facilitate a greater understanding of the effects of relative camber on the Aerodynamic Performance improvement of asymmetrical blunt trailing-edge modification. The mathematical expression of the blunt trailing-edge modification profile is established using the cubic spline function, and S812, S816 and S830 airfoils are modified to be asymmetrical blunt trailing-edge airfoils with different thicknesses. The prediction capabilities of two turbulence models, the k-ω SST model and the S-A model, are assessed. It is observed that the k-ω SST model predicts the lift and drag coefficients of S812 airfoil more accurately through comparison with experimental data. The best trailing-edge thickness and thickness distribution ratio are obtained by comparing the Aerodynamic Performance of the modifications with different trailing-edge thicknesses and distribution ratios. It is, furthermore, investigated that the Aerodynamic Performance of original airfoils and their modifications with the best thickness of 2% c and distribution ratio being 0:4 so as to analyze the increments of lift and drag coefficients and lift–drag ratio. Results indicate that with the increase of relative camber, there are relatively small differences in the lift coefficient increments of airfoils whose relative cambers are less than 1.81%, and the lift coefficient increment of airfoil with the relative camber more than 1.81% obviously decreases for the angle of attack less than 6.3°. The drag coefficient increment of S830 airfoil is higher than that of S816 airfoil, and those of these two airfoils mainly decrease with the angle of attack. The average lift–drag ratio increment of S816 airfoil with the relative camber of 1.81% at different angles of attack ranging from 0.1° to 20.2° is the largest, closely followed by S812 airfoil. The lift–drag ratio increment of S830 airfoil is negative as the angle of attack exceeds 0.1°. Thus, the airfoil with medium camber is more suited to the asymmetrical blunt trailing-edge modification.

  • numerical study of the Aerodynamic Performance of blunt trailing edge airfoil considering the sensitive roughness height
    International Journal of Hydrogen Energy, 2017
    Co-Authors: Xu Zhang, Gege Wang, Mengjie Zhang, Wei Li
    Abstract:

    Abstract For rough wind turbine airfoil and its blunt trailing-edge modification, the Aerodynamic Performance has been numerically investigated to facilitate a greater understanding of the effects of the blunt trailing-edge modification on the Aerodynamic Performance enhancement of airfoil with sensitive roughness height. The S834 airfoil from National Renewable Energy Laboratory is used for the simulation. The lift and drag coefficients of S834 airfoil with smooth or rough surface are calculated by the k-ω SST turbulence model, and are compared with wind tunnel test results. The Aerodynamic Performance of airfoils with different roughness heights is studied to obtain the sensitive roughness heights of suction and pressure surfaces. The mathematical expression of the blunt trailing-edge airfoil profile is established using the coordinate's rotation combined with the zoom coefficient of coordinate. Then, the S834 airfoil with sensitive roughness height is modified to be symmetrical blunt trailing-edge modification, and the lift and drag coefficients and the lift-drag ratio are also calculated and analyzed. Results indicate that the sensitive roughness height of suction surface is 0.5 mm, and the pressure surface is insensitive to the roughness height. Through the blunt trailing-edge modification, the lift coefficient and the maximum lift-drag ratio obviously increase for rough airfoil, and the sensitivity of airfoil to roughness height is reduced. The research provides significant guidance for designing the wind turbine airfoil under conditions of rough blade.

  • numerical simulation of the effect of relative thickness on Aerodynamic Performance improvement of asymmetrical blunt trailing edge modification
    Renewable Energy, 2015
    Co-Authors: Xu Zhang, Wei Li
    Abstract:

    In this paper, the Aerodynamic Performance of wind turbine airfoils with different relative thicknesses and their modifications has been numerically investigated to facilitate a greater understanding of the effects of maximum relative thickness and its position on the Aerodynamic Performance improvement of asymmetrical blunt trailing-edge modification. The lift and drag coefficients of airfoil NACA4415 are calculated with the k-ω SST turbulence model, and are compared with experimental data to validate the simulation accuracy of the Computational Fluid Dynamics (CFD) approach. The airfoils with different relative thicknesses are modified to be asymmetrical blunt trailing-edge airfoils by means of the software Xfoil. The best trailing-edge thickness distribution ratio is obtained by comparing the Aerodynamic Performance of the modifications with different distribution ratios. The Aerodynamic Performance of original airfoils and their asymmetrical modifications with the best thickness distribution ratio being 1:3 is investigated to analyze the increments of lift and drag coefficients and lift-drag ratio. Results indicate that with the increasing of relative thickness, the lift coefficient increment of NACA4418 airfoil is the smallest for the angle of attack more than 9°, and the drag coefficient increment as a whole decreases first and then increases, but the average lift-drag ratio increment of NACA4412 airfoil is the largest, closely followed by NACA4415 airfoil. It is also showed that with the relative thickness position close to the leading-edge, the increments of lift and drag coefficients decrease and increase for the angle of attack more than a certain value, respectively, and the average lift-drag ratio increment of NACA4415 airfoil is positive and larger than those of NACA4415-mod25 and NACA4415-mod20 airfoils. Therefore, the medium thickness airfoil whose relative thickness position is away from the leading-edge is more suited to the asymmetrical blunt trailing-edge modification.

Xu Zhang - One of the best experts on this subject based on the ideXlab platform.

  • effect of relative camber on the Aerodynamic Performance improvement of asymmetrical blunt trailing edge modification
    Journal of Engineering Thermophysics, 2017
    Co-Authors: Xu Zhang, G G Wang, M.j. Zhang, Wei Li
    Abstract:

    In this paper, the Aerodynamic Performance of the S series of wind turbine airfoils with different relative cambers and their modifications is numerically studied to facilitate a greater understanding of the effects of relative camber on the Aerodynamic Performance improvement of asymmetrical blunt trailing-edge modification. The mathematical expression of the blunt trailing-edge modification profile is established using the cubic spline function, and S812, S816 and S830 airfoils are modified to be asymmetrical blunt trailing-edge airfoils with different thicknesses. The prediction capabilities of two turbulence models, the k-ω SST model and the S-A model, are assessed. It is observed that the k-ω SST model predicts the lift and drag coefficients of S812 airfoil more accurately through comparison with experimental data. The best trailing-edge thickness and thickness distribution ratio are obtained by comparing the Aerodynamic Performance of the modifications with different trailing-edge thicknesses and distribution ratios. It is, furthermore, investigated that the Aerodynamic Performance of original airfoils and their modifications with the best thickness of 2% c and distribution ratio being 0:4 so as to analyze the increments of lift and drag coefficients and lift–drag ratio. Results indicate that with the increase of relative camber, there are relatively small differences in the lift coefficient increments of airfoils whose relative cambers are less than 1.81%, and the lift coefficient increment of airfoil with the relative camber more than 1.81% obviously decreases for the angle of attack less than 6.3°. The drag coefficient increment of S830 airfoil is higher than that of S816 airfoil, and those of these two airfoils mainly decrease with the angle of attack. The average lift–drag ratio increment of S816 airfoil with the relative camber of 1.81% at different angles of attack ranging from 0.1° to 20.2° is the largest, closely followed by S812 airfoil. The lift–drag ratio increment of S830 airfoil is negative as the angle of attack exceeds 0.1°. Thus, the airfoil with medium camber is more suited to the asymmetrical blunt trailing-edge modification.

  • numerical study of the Aerodynamic Performance of blunt trailing edge airfoil considering the sensitive roughness height
    International Journal of Hydrogen Energy, 2017
    Co-Authors: Xu Zhang, Gege Wang, Mengjie Zhang, Wei Li
    Abstract:

    Abstract For rough wind turbine airfoil and its blunt trailing-edge modification, the Aerodynamic Performance has been numerically investigated to facilitate a greater understanding of the effects of the blunt trailing-edge modification on the Aerodynamic Performance enhancement of airfoil with sensitive roughness height. The S834 airfoil from National Renewable Energy Laboratory is used for the simulation. The lift and drag coefficients of S834 airfoil with smooth or rough surface are calculated by the k-ω SST turbulence model, and are compared with wind tunnel test results. The Aerodynamic Performance of airfoils with different roughness heights is studied to obtain the sensitive roughness heights of suction and pressure surfaces. The mathematical expression of the blunt trailing-edge airfoil profile is established using the coordinate's rotation combined with the zoom coefficient of coordinate. Then, the S834 airfoil with sensitive roughness height is modified to be symmetrical blunt trailing-edge modification, and the lift and drag coefficients and the lift-drag ratio are also calculated and analyzed. Results indicate that the sensitive roughness height of suction surface is 0.5 mm, and the pressure surface is insensitive to the roughness height. Through the blunt trailing-edge modification, the lift coefficient and the maximum lift-drag ratio obviously increase for rough airfoil, and the sensitivity of airfoil to roughness height is reduced. The research provides significant guidance for designing the wind turbine airfoil under conditions of rough blade.

  • numerical simulation of the effect of relative thickness on Aerodynamic Performance improvement of asymmetrical blunt trailing edge modification
    Renewable Energy, 2015
    Co-Authors: Xu Zhang, Wei Li
    Abstract:

    In this paper, the Aerodynamic Performance of wind turbine airfoils with different relative thicknesses and their modifications has been numerically investigated to facilitate a greater understanding of the effects of maximum relative thickness and its position on the Aerodynamic Performance improvement of asymmetrical blunt trailing-edge modification. The lift and drag coefficients of airfoil NACA4415 are calculated with the k-ω SST turbulence model, and are compared with experimental data to validate the simulation accuracy of the Computational Fluid Dynamics (CFD) approach. The airfoils with different relative thicknesses are modified to be asymmetrical blunt trailing-edge airfoils by means of the software Xfoil. The best trailing-edge thickness distribution ratio is obtained by comparing the Aerodynamic Performance of the modifications with different distribution ratios. The Aerodynamic Performance of original airfoils and their asymmetrical modifications with the best thickness distribution ratio being 1:3 is investigated to analyze the increments of lift and drag coefficients and lift-drag ratio. Results indicate that with the increasing of relative thickness, the lift coefficient increment of NACA4418 airfoil is the smallest for the angle of attack more than 9°, and the drag coefficient increment as a whole decreases first and then increases, but the average lift-drag ratio increment of NACA4412 airfoil is the largest, closely followed by NACA4415 airfoil. It is also showed that with the relative thickness position close to the leading-edge, the increments of lift and drag coefficients decrease and increase for the angle of attack more than a certain value, respectively, and the average lift-drag ratio increment of NACA4415 airfoil is positive and larger than those of NACA4415-mod25 and NACA4415-mod20 airfoils. Therefore, the medium thickness airfoil whose relative thickness position is away from the leading-edge is more suited to the asymmetrical blunt trailing-edge modification.

Zhongquan Zheng - One of the best experts on this subject based on the ideXlab platform.

  • numerical investigation on Aerodynamic Performance of a novel vertical axis wind turbine with adaptive blades
    Energy Conversion and Management, 2016
    Co-Authors: Ying Wang, Xiaojing Sun, Xiaohua Dong, Bing Zhu, Diangui Huang, Zhongquan Zheng
    Abstract:

    In this paper, a novel Darrieus vertical axis wind turbine was designed whose blade can be deformed automatically into a desired geometry and thus achieve a better Aerodynamic Performance. A series of numerical simulations were conducted by utilizing the United Computational Fluid Dynamics code. Firstly, analysis and comparison of the Performance of undeformed and deformed blades for the rotors having different blades were conducted. Then, the power characteristics of each simulated turbine were summarized and a universal tendency was found. Secondly, investigation on the effect of blade number and solidity on the power Performance of Darrieus vertical axis wind turbine with deformable and undeformable blades was carried out. The results indicated that compared to conventional turbines with same solidity, the maximum percentage increase in power coefficient that the low solidity turbine with three deformable blades can achieve is about 14.56%. When solidity is high and also turbine operates at low tip speed ratio of less than the optimum value, the maximum power coefficient increase for the turbines with two and four deformable blades are 7.51% and 8.07%, respectively. However, beyond the optimal tip speed ratio, the power improvement of the turbine using the deformable blades seems not significant and even slightly worse than the conventional turbines. The last section studied the transient behavior of vortex and turbulent flow structures around the deformable rotor blade to explore the physical mechanism of improving Aerodynamic Performance. The adaptive blades could obviously suppress the separation of flow from the blade surfaces.

Bert Blocken - One of the best experts on this subject based on the ideXlab platform.

  • characterization of Aerodynamic Performance of vertical axis wind turbines impact of operational parameters
    Energy Conversion and Management, 2018
    Co-Authors: Abdolrahim Rezaeiha, H Montazeri, Bert Blocken
    Abstract:

    Abstract Vertical axis wind turbines (VAWTs) have received growing interest for off-shore application and in the urban environments mainly due to their omni-directional capability, scalability, robustness, low noise and costs. However, their Aerodynamic Performance is still not comparable with their horizontal axis counterparts. To enhance their Performance, the impact of operational parameters such as tip speed ratio (λ), Reynolds number (Rec) and turbulence intensity (TI) on their power Performance and Aerodynamics needs to be deeply understood. The current study, therefore, intends to systematically investigate the effect of these parameters in order to provide a deeper insight into their impact on the Aerodynamic Performance of VAWTs. For this investigation, a Darrieus H-type VAWT has been employed. A wide range of the parameters is considered: λ = 1.2–6.0, Rec = 0.3 × 105–4.2 × 105 and TI = 0%–30% to analyze the turbine Performance, turbine wake and dynamic loads on blades. High-fidelity computational fluid dynamics (CFD), extensively validated with experimental data, are employed. The results show that (i) variable-speed operation maintaining the optimal λ at different wind speeds improves the turbine power coefficient, e.g. up to 168% at 4 m/s, while keeping an almost constant thrust coefficient, (ii) the turbine Performance and wake are Re-dependent up to the highest Rec studied, (iii) large TI (> 5%) improves the turbine Performance in dynamic stall by promoting the laminar-to-turbulent transition and delaying stall on blades, however it deteriorates the optimal Performance by introducing extra skin friction drag. The findings of the current study can support more accurate Performance prediction of VAWTs for various operating conditions and can help the improvement of the Aerodynamic Performance of VAWTs.

Kiwahn Ryu - One of the best experts on this subject based on the ideXlab platform.

  • Aerodynamic Performance prediction of a 30 kw counter rotating wind turbine system
    Renewable Energy, 2005
    Co-Authors: Sung Nam Jung, Kiwahn Ryu
    Abstract:

    Abstract In the present work, the Aerodynamic Performance prediction of a unique 30 kW counter-rotating (C/R) wind turbine system, which consists of the main rotor and the auxiliary rotor, has been investigated by using the quasi-steady strip theory. The near wake behavior of the auxiliary rotor that is located upwind of the main rotor is taken into consideration in the Performance analysis of the turbine system by using the wind tunnel test data obtained for scaled model rotors. The relative size and the optimum placement of the two rotors are investigated through use of the momentum theory combined with the experimental wake model. In addition, the Performance prediction results along with the full-scale field test data obtained for C/R wind turbine system are compared with those of the conventional single rotor system and demonstrated the effectiveness of the current C/R turbine system.

  • Aerodynamic Performance prediction of a 30kw counter rotating wind turbine system
    Renewable Energy, 2005
    Co-Authors: Sung Nam Jung, Kiwahn Ryu
    Abstract:

    In the present work, the Aerodynamic Performance prediction of a unique 30kW counter-rotating (C/R) wind turbine system, which consists of the main rotor and the auxiliary rotor, has been investigated by using the quasi-steady strip theory. The near wake behavior of the auxiliary rotor that is located upwind of the main rotor is taken into consideration in the Performance analysis of the turbine system by using the wind tunnel test data obtained for scaled model rotors. The relative size and the optimum placement of the two rotors are investigated through use of the momentum theory combined with the experimental wake model. In addition, the Performance prediction results along with the full-scale field test data obtained for C/R wind turbine system are compared with those of the conventional single rotor system and demonstrated the effectiveness of the current C/R turbine system.