The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform

Martin Otto Laver Hansen - One of the best experts on this subject based on the ideXlab platform.

  • identification of variations of angle of attack and Lift Coefficient for a large horizontal axis wind turbine
    15TH European Turbulence Conference, 2015
    Co-Authors: Abdolrahim Rezaeiha, Maziar Arjomandi, Marios Kotsonis, Martin Otto Laver Hansen
    Abstract:

    The current paper investigates the effects of various elements including turbulence, wind shear, yawed inflow, tower shadow, gravity, mass and aerodynamic imbalances on variations of angle of attack and Lift Coefficient for a large horizontal-axis wind turbine. It will identify the individual and the aggregate effect of elements on variations of mean value and standard deviation of the angle of attack and Lift Coefficient in order to distinguish the major contributing factors. The results of the current study is of paramount importance in the design of active load control systems for wind turbine.

James L Tangler - One of the best experts on this subject based on the ideXlab platform.

  • Blade design trade-offs using low-Lift airfoils for stall-regulated HAWTs
    Journal of Solar Energy Engineering, 1999
    Co-Authors: Philippe Giguere, Michael S. Selig, James L Tangler
    Abstract:

    A systematic blade design study was conducted to explore the trade-offs in using low-Lift airfoils for a 750-kilowatt stall-regulated wind turbine. Tip-region airfoils having a maximum-Lift Coefficient ranging from 0.7-1.2 were considered in this study, with the main objective of identifying the practical lower limit for the maximum-Lift Coefficient. Blades were optimized for both maximum annual energy production and minimum cost of energy using a method that takes into account aerodynamic and structural considerations. The results indicate that the effect of the maximum-Lift Coefficient on the cost of energy is small with a slight advantage to the highest maximum Lift Coefficient case considered in this study. As a consequence, higher maximum Lift Coefficient airfoils for the tip-region of the blade become more desirable as machine size increases, provided the airfoils yield acceptable stall characteristics. The conclusions are applicable to large wind turbines that use passive or active stall to regulate peak power.

  • blade design trade offs using low Lift airfoils for stall regulated hawts
    Journal of Solar Energy Engineering-transactions of The Asme, 1999
    Co-Authors: Philippe Giguere, Michael S. Selig, James L Tangler
    Abstract:

    A systematic blade design study was conducted to explore the trade-offs in using low-Lift airfoils for a 750-kilowatt stall-regulated wind turbine. Tip-region airfoils having a maximum Lift Coefficient ranging from 0.7-1.2 were considered in this study, with the main objective of identifying the practical lower limit for the maximum Lift Coefficient. Blades were optimized for both maximum annual energy production and minimum cost of energy using a method that takes into account aerodynamic and structural considerations. The results indicate that reducing the maximum Lift Coefficient below the upper limit considered in this study increases the cost of energy independently of the wind regime. As a consequence, higher maximum Lift Coefficient airfoils for the tip-region of the blade become more desirable as machine size increases, as long as they provide gentle stall characteristics. The conclusions are applicable to large wind turbines that use passive or active stall to regulate peak power.

  • Wind tunnel test of the S814 thick root airfoil
    Journal of Solar Energy Engineering, 1996
    Co-Authors: D.m. Somers, James L Tangler
    Abstract:

    The objective of this wind-tunnel test was to verify the predictions of the Eppler Airfoil Design and Analysis Code for a very thick airfoil having a high maximum Lift Coefficient designed to be largely insensitive to leading-edge roughness effects. The 24 percent thick S814 airfoil was designed with these characteristics to accommodate aerodynamic and structural considerations for the root region of a wind-turbine blade. In addition, the airfoil`s maximum Lift-to-drag ratio was designed to occur at a high Lift Coefficient. To accomplish the objective, a two-dimensional wind tunnel test of the S814 thick root airfoil was conducted in January 1994 in the low-turbulence wind tunnel of the Delft University of Technology Low Speed Laboratory, The Netherlands. Data were obtained with transition free and transition fixed for Reynolds numbers of 0.7, 1.0, 1.5, 2.0, and 3.0 {times} 10{sup 6}. For the design Reynolds number of 1.5 {times} 10{sup 6}, the maximum Lift Coefficient with transition free is 1.32, which satisfies the design specification. However, this value is significantly lower than the predicted maximum Lift Coefficient of almost 1.6. With transition fixed at the leading edge, the maximum Lift Coefficient is 1.22. The small difference in maximum Lift Coefficient between the transition-freemore » and transition-fixed conditions demonstrates the airfoil`s minimal sensitivity to roughness effects. The S814 root airfoil was designed to complement existing NREL low maximum-Lift-Coefficient tip-region airfoils for rotor blades 10 to 15 meters in length.« less

Hua Wang - One of the best experts on this subject based on the ideXlab platform.

  • prediction of Lift Coefficient for tandem wing configuration or multiple Lifting surface system using prandtl s Lifting line theory
    International Journal of Aerospace Engineering, 2018
    Co-Authors: Hao Cheng, Hua Wang
    Abstract:

    In tandem airfoil configuration or multiple-Lifting-surface layouts, due to the flow interaction among their Lifting surfaces, the aerodynamic characteristics can be affected by each other. In accordance with Prandtl’s classical Lifting-line theory, a method to calculate the section Lift Coefficient for the tandem wing configuration or multiple-Lifting-surface system is presented. In that method, the form of Fourier sine series is used to express the variation of the section circulation which changes continuously along the wingspan. The accuracy of the numerical solutions obtained by the method has been validated by the data obtained from computational fluid dynamics and tunnel experiment. By varying the design parameters, such as the gap, the stagger, the incidence angle, the wingspan, the taper ratio as well as the aspect ratio, a series of tandem wing configurations are tested to analyze the Lift Coefficient and the induced drag of each Lifting surface. From the results, it can be seen that the bigger negative gap and stagger can produce better Lift characteristic for tandem wing configuration. Besides, it will also be beneficial for the Lift characteristic when the incidence angle and the wingspan of fore wing are appropriately declined or if the incidence angle and the wingspan of hind wing are appropriately increased.

  • Prediction of Lift Coefficient for Tandem Wing Configuration or Multiple-Lifting-Surface System Using Prandtl’s Lifting-Line Theory
    Hindawi Limited, 2018
    Co-Authors: Hao Cheng, Hua Wang
    Abstract:

    In tandem airfoil configuration or multiple-Lifting-surface layouts, due to the flow interaction among their Lifting surfaces, the aerodynamic characteristics can be affected by each other. In accordance with Prandtl’s classical Lifting-line theory, a method to calculate the section Lift Coefficient for the tandem wing configuration or multiple-Lifting-surface system is presented. In that method, the form of Fourier sine series is used to express the variation of the section circulation which changes continuously along the wingspan. The accuracy of the numerical solutions obtained by the method has been validated by the data obtained from computational fluid dynamics and tunnel experiment. By varying the design parameters, such as the gap, the stagger, the incidence angle, the wingspan, the taper ratio as well as the aspect ratio, a series of tandem wing configurations are tested to analyze the Lift Coefficient and the induced drag of each Lifting surface. From the results, it can be seen that the bigger negative gap and stagger can produce better Lift characteristic for tandem wing configuration. Besides, it will also be beneficial for the Lift characteristic when the incidence angle and the wingspan of fore wing are appropriately declined or if the incidence angle and the wingspan of hind wing are appropriately increased

Talel Ben Mbarek - One of the best experts on this subject based on the ideXlab platform.

  • reduced order model for the Lift Coefficient of an airfoil equipped with extrados and or trailing edge flexible flaps
    Computers & Fluids, 2019
    Co-Authors: Chedhli Hafien, Talel Ben Mbarek
    Abstract:

    Abstract To treat the problem of low aerodynamic performance and high unsteadiness of a flow around an airfoil at low Reynolds numbers, passive actuation techniques have been used. A NACA0012 airfoil at Re = 103 and high incidence angles (15° and 20°) equipped with a trailing edge and/or extrados flexible flaps has been studied. The two-way Fluid-Structure Interaction has been studied by coupling the “CFD-Fluent” and “Transient Structural” systems in the ANSYS-Workbench 15.0 software. A reduced order model of the Lift Coefficient oscillation based on the van der Pol oscillator has been formulated. The analytical model helps analyze and understand the underlying physics of the nonlinear system. The characteristics of the limit cycle oscillation of the Lift Coefficient have been modified by decreasing the amplitudes proportional to the principal and second Strouhal numbers and by increasing the amplitude proportional to the third Strouhal number. These modifications are influenced by the interaction between the detached flexible flap and the trailing edge vortex downstream of the airfoil, which provokes the change in the flow topology. It has also been shown that the presence of the trailing edge flexible flap has the effect of increasing the Lift Coefficient and reducing the unsteadiness Coefficient.

  • Reduced order model for the Lift Coefficient of an airfoil equipped with extrados and/or trailing edge flexible flaps
    Computers & Fluids, 2019
    Co-Authors: Chedhli Hafien, Talel Ben Mbarek
    Abstract:

    Abstract To treat the problem of low aerodynamic performance and high unsteadiness of a flow around an airfoil at low Reynolds numbers, passive actuation techniques have been used. A NACA0012 airfoil at Re = 103 and high incidence angles (15° and 20°) equipped with a trailing edge and/or extrados flexible flaps has been studied. The two-way Fluid-Structure Interaction has been studied by coupling the “CFD-Fluent” and “Transient Structural” systems in the ANSYS-Workbench 15.0 software. A reduced order model of the Lift Coefficient oscillation based on the van der Pol oscillator has been formulated. The analytical model helps analyze and understand the underlying physics of the nonlinear system. The characteristics of the limit cycle oscillation of the Lift Coefficient have been modified by decreasing the amplitudes proportional to the principal and second Strouhal numbers and by increasing the amplitude proportional to the third Strouhal number. These modifications are influenced by the interaction between the detached flexible flap and the trailing edge vortex downstream of the airfoil, which provokes the change in the flow topology. It has also been shown that the presence of the trailing edge flexible flap has the effect of increasing the Lift Coefficient and reducing the unsteadiness Coefficient.

Haecheon Choi - One of the best experts on this subject based on the ideXlab platform.

  • Sectional Lift Coefficient of a rotating wing at low Reynolds numbers
    Journal of Mechanical Science and Technology, 2015
    Co-Authors: Jieun Kim, Jihoon Kweon, Haecheon Choi
    Abstract:

    We study the characteristics of the sectional Lift Coefficient (C L,S ) of low-aspect-ratio wings in rotating motion at low Reynolds number (Re = 136), by conducting three-dimensional numerical simulations. Three different shapes of thin-plate wings (fruit-fly, rectangular, and triangular wings) are considered but keeping their aspect ratio (wing span/wing chord) the same at 3.74. Each wing rotates at a constant angular velocity and the angle of attack (α) is fixed during rotation. During rotation, the wing is exposed to the downward flows generated from the previous rotation, and thus C L,S is overall reduced due to the decrease in the effective angle of attack. At low α’s, C L,S becomes almost constant on the whole span. At high α’s, C L,S on the wing mid-section is inversely proportional to the radial position. The radial distribution of the sectional Lift Coefficient is less affected by the wing planform, while the Lift Coefficient significantly depends on the wing planforms. Finally, we show that the effect of the Reynolds number on the sectional Lift Coefficient is insignificant at low angle of attack but becomes important at high angle of attack.

  • Sectional Lift Coefficient of a flapping wing in hovering motion
    Physics of Fluids, 2010
    Co-Authors: Jihoon Kweon, Haecheon Choi
    Abstract:

    We investigate the behavior of sectional Lift Coefficient of a flapping wing of a fruit-fly in hovering motion. Through three-dimensional numerical simulations, we show that during the stroke, the sectional Lift Coefficient significantly varies in time as well as in the spanwise direction owing to complex interactions between the wing and vortices in the wake. However, the time-averaged sectional Lift force Coefficient is inversely proportional to the spanwise distance from the rotation center except very near the wing-tip region. This is because the wing-tip vortex significantly decreases the Lift force on the wing-tip region during and after midstroke.