Aerodynamic Loads on a Darrieus Rotor Blade

1983 ◽  
Vol 105 (1) ◽  
pp. 53-58 ◽  
Author(s):  
R. E. Wilson ◽  
P. B. S. Lissaman ◽  
M. James ◽  
W. R. McKie
Keyword(s):  
Rotor Blade ◽  
Accurate Determination ◽  
Vortex Sheet ◽  
Numerical Results ◽  
Speed Ratio ◽  
Aerodynamic Loads ◽  
Tip Speed Ratio ◽  
Circle Plane ◽  
Darrieus Rotor

A free-vortex analysis of a Darrieus rotor blade in nonsteady motion has been developed. The method uses the circle theorem to map a moving airfoil into the circle plane. The wake is modeled using point vortices. Nascent vortex strength and position are determined from the Kutta condition so that the nascent vortex has the same strength as a vortex sheet of uniform strength. The force on the airfoil is determined by two methods, integration of the pressure over the plate and from the impulse of the wake vortices. Both methods yield the same numerical results. A comparison with an analytical solution for a plunging airfoil gives excellent agreement. Results are shown for a one-bladed Darrieus Rotor at a tip speed ratio of three and two chord sizes. The numerical results indicate that the forces and moment on a Darrieus Rotor blade may be adequately approximated by quasisteady relationships although accurate determination of the local velocity and circulation are still required.

scholarly journals Numerical simulation and experimental study of blade pitch effect on Darrieus straight-bladed wind turbine with high solidity: A case study under realistic conditions

2020 ◽  
Author(s):  
Milad Babadi Soultanzadeh ◽  
Alireza Moradi
Keyword(s):  
Wind Turbine ◽  
Numerical Method ◽  
Pitch Angle ◽  
Numerical Results ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Regulation System ◽  
Lower Velocity ◽  
Realistic Condition ◽  
Tip Speed Ratio

Abstract Numerical and experimental studies were performed to examined the influence of pitch angle on the aerodynamic performance of a small Darrieus straight blade vertical axis wind turbine with high solidity and pitch regulation system under a realistic condition. By comparing experimental and numerical results, numerical results were validated. The power coefficient was measured and calculated at different tip speed ratios and for two pitch angles 0 and 5. The results revealed that 5 degrees increase in the pitch angle led to 25% elevation in the maximum value of the power coefficient (performance coefficient). Also, the numerical results showed higher accuracy at lower tip speed ratios for both pitch angles. After numerical method validation, numerical method employed to calculate the coefficient of performance and coefficient of torque function of Azimuth position as well as the flow field in the rotor affected zone and lateral distance. According to the numerical results, vorticity generation increased by the rise in the pitch angle at a constant tip speed ratio; the maximum performance coefficient occurred at a lower tip speed ratio with elevation in the pitch angle; finally, the increment in the pitch angle led to lower velocity profile in lateral distances of the rotor.

Fixed Wake Theory for Vertical Axis Wind Turbines

1983 ◽  
Vol 105 (4) ◽  
pp. 389-393 ◽  
Author(s):  
R. E. Wilson ◽  
S. N. Walker
Keyword(s):  
Wind Turbines ◽  
Vertical Axis ◽  
Explicit Calculation ◽  
Speed Ratio ◽  
Test Results ◽  
Vortex Methods ◽  
Tip Speed Ratio ◽  
Vertical Axis Wind Turbines ◽  
Darrieus Rotor ◽  
Good Agreement

A theory for vertical axis wind turbines has been developed using a fixed wake approach. The theory combines some of the best features of vortex and streamtube approaches. This approach accounts for flow differences between fore-and-aft-blade positions that are predicted by vortex methods while retaining the low computation costs associated with streamtube theories. The theory is applied to high tip speed ratio operation of a Darrieus Rotor where the use of linear aerodynamics results in explicit calculation of the induced velocities. Comparison to test results shows good agreement.

scholarly journals Determination of the angle of attack on a research wind turbine rotor blade using surface pressure measurements

2020 ◽  
Vol 5 (4) ◽  
pp. 1771-1792
Author(s):  
Rodrigo Soto-Valle ◽  
Sirko Bartholomay ◽  
Jörg Alber ◽  
Marinos Manolesos ◽  
Christian Navid Nayeri ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Rotor Blade ◽  
Angle Of Attack ◽  
Turbine Rotor ◽  
Speed Ratio ◽  
Horizontal Axis Wind Turbine ◽  
Turbine Rotor Blade ◽  
Wide Range ◽  
Wind Turbine Rotor

Abstract. In this paper, a method to determine the angle of attack on a wind turbine rotor blade using a chordwise pressure distribution measurement was applied. The approach used a reduced number of pressure tap data located close to the blade leading edge. The results were compared with the measurements from three external probes mounted on the blade at different radial positions and with analytical calculations. Both experimental approaches used in this study are based on the 2-D flow assumption; the pressure tap method is an application of the thin airfoil theory, while the probe method applies geometrical and induction corrections to the measurement data. The experiments were conducted in the wind tunnel at the Hermann Föttinger Institut of the Technische Universität Berlin. The research turbine is a three-bladed upwind horizontal axis wind turbine model with a rotor diameter of 3 m. The measurements were carried out at rated conditions with a tip speed ratio of 4.35, and different yaw and pitch angles were tested in order to compare the approaches over a wide range of conditions. Results show that the pressure tap method is suitable and provides a similar angle of attack to the external probe measurements as well as the analytical calculations. This is a significant step for the experimental determination of the local angle of attack, as it eliminates the need for external probes, which affect the flow over the blade and require additional calibration.

scholarly journals Performance Analysis and Optimization of a Vertical-Axis Wind Turbine with a High Tip-Speed Ratio

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 996
Author(s):  
Liang Li ◽  
Inderjit Chopra ◽  
Weidong Zhu ◽  
Meilin Yu
Keyword(s):  
Wind Turbine ◽  
Pitch Angle ◽  
Angle Of Attack ◽  
Vertical Axis ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine ◽  
Aerodynamic Loads ◽  
Tip Speed Ratio ◽  
Aerodynamic Model ◽  
Lift And Drag

In this work, the aerodynamic performance and optimization of a vertical-axis wind turbine with a high tip-speed ratio are theoretically studied on the basis of the two-dimensional airfoil theory. By dividing the rotating plane of the airfoil into the upwind and downwind areas, the relationship among the angle of attack, azimuth, pitch angle, and tip-speed ratio is derived using the quasi-steady aerodynamic model, and aerodynamic loads on the airfoil are then obtained. By applying the polynomial approximation to functions of lift and drag coefficients with the angle of attack for symmetric and asymmetric airfoils, respectively, explicit expressions of aerodynamic loads as functions of the angle of attack are obtained. The performance of a fixed-pitch blade is studied by employing a NACA0012 model, and influences of the tip speed ratio, pitch angle, chord length, rotor radius, incoming wind speed and rotational speed on the performance of the blade are discussed. Furthermore, the optimization problem based on the dynamic-pitch method is investigated by considering the maximum value problem of the instantaneous torque as a function of the pitch angle. Dynamic-pitch laws for symmetric and asymmetric airfoils are derived.

A comprehensive analysis of aerodynamic flow around H-Darrieus rotor with camber-bladed profile

2018 ◽  
Vol 43 (5) ◽  
pp. 459-475 ◽  
Author(s):  
Khaled Souaissa ◽  
Moncef Ghiss ◽  
Mouldi Chrigui ◽  
Hatem Bentaher ◽  
Aref Maalej
Keyword(s):  
Wind Turbine ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Vertical Axis ◽  
Speed Ratio ◽  
Blade Profile ◽  
Vertical Axis Wind Turbine ◽  
Tip Speed Ratio ◽  
Torque Coefficient ◽  
Darrieus Rotor

Improving the H-Darrieus rotor is often followed by the investigation of the influence of the turbine’s parameter design, notably, the aspect ratio, the solidity ( σ), the tip speed ratio, and the airfoil profile shape. In this work, we are interested in both the aerodynamic flows around a straight cambered blade profile and the rotor turbine wake separation of a Darrieus vertical axis wind turbine. The aim of this study is to better understand the evolution of the instantaneous torque and the generated-separated blade vortex during full rotation. Indeed, a three-dimensional computational fluid dynamics model of a vertical axis wind turbine with a straight cambered blade profile NACA4312 operating over a large range of tip speed ratio is considered. The flows are governed by Reynolds-averaged Navier–Stokes equations and the turbulence is modeled with shear stress transport formulations k- ω. This research revealed a high correlation between the evolution of the torque coefficient and the generated-separated blades vortex. In particular, a good correlation between the maximum tip vortices size and the torque coefficient peak is demonstrated.

The Analysis of the Flutter Region of Wind Turbine Blade

2013 ◽  
Vol 423-426 ◽  
pp. 1520-1523
Author(s):  
Hao Wang ◽  
Bing Ma ◽  
Jiao Jiao Ding
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Aerodynamic Force ◽  
Angular Displacement ◽  
Wind Turbine Blade ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
Flutter Analysis ◽  
The Given

As the wind turbine blade is becoming larger and larger, the flutter of the wind turbine blade has been paid great attention by many fields. The flutter region of the wind turbine blade airfoil was focused on. The equation of motion for the flutter of blade airfoil was established, based on the simplified aerodynamic force and torque. The flutter analysis of wind turbine blade was carried out with the four-order Runge-Kutta methods, and so the flutter region of the blade airfoil can be obtained. The results show that, there are two critical tip speed ratios for the given blade airfoil. When the tip speed ratio is below the low critical speed ratio, the blade airfoil is convergent. At the low tip speed ratio, the blade airfoil system will become divergent from convergent condition. When the tip speed ratio is between the low critical tip speed ratio and the high one, the blade airfoil system will diverge. At the high tip speed ratio, the system will become convergent from divergent condition. When the tip speed ratio is above the high critical tip speed ratio, the blade airfoil system will converge again. In addition, the torsional angular displacement and velocity always keep convergent, the flap velocity is slightly divergent, because they are not sensible to the change of the tip speed ratio, and they are difficult to cause flutter, so the torsional motion will be more stable than flap motion for the given blade airfoil. It can provide one of references for the determination of the blade airfoil.

A quantitative approach to inner shell losses

1978 ◽  
Vol 36 (1) ◽  
pp. 526-527 ◽  
Author(s):  
R.D. Leapman ◽  
P. Rez ◽  
D.F. Mayers
Keyword(s):  
Energy Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Accurate Determination ◽  
Background Intensity ◽  
Core Excitation ◽  
Quantitative Basis ◽  
Cross Section Differential ◽  
Bound Electrons

Microanalysis by EELS has been developing rapidly and though the general form of the spectrum is now understood there is a need to put the technique on a more quantitative basis (1,2). Certain aspects important for microanalysis include: (i) accurate determination of the partial cross sections, σx(α,ΔE) for core excitation when scattering lies inside collection angle a and energy range ΔE above the edge, (ii) behavior of the background intensity due to excitation of less strongly bound electrons, necessary for extrapolation beneath the signal of interest, (iii) departures from the simple hydrogenic K-edge seen in L and M losses, effecting σx and complicating microanalysis. Such problems might be approached empirically but here we describe how computation can elucidate the spectrum shape.The inelastic cross section differential with respect to energy transfer E and momentum transfer q for electrons of energy E0 and velocity v can be written as

Fast calibration of CBED patterns for quantitative analysis

1993 ◽  
Vol 51 ◽  
pp. 674-675
Author(s):  
M.A. Gribelyuk ◽  
M. Rühle
Keyword(s):  
Reciprocal Lattice ◽  
Accurate Determination ◽  
Incident Beam ◽  
Crystal Thickness ◽  
Structure Model ◽  
Beam Direction ◽  
Transmitted Beam ◽  
Reciprocal Vector ◽  
On Line

A new method is suggested for the accurate determination of the incident beam direction K, crystal thickness t and the coordinates of the basic reciprocal lattice vectors V1 and V2 (Fig. 1) of the ZOLZ plans in pixels of the digitized 2-D CBED pattern. For a given structure model and some estimated values Vest and Kest of some point O in the CBED pattern a set of line scans AkBk is chosen so that all the scans are located within CBED disks.The points on line scans AkBk are conjugate to those on A0B0 since they are shifted by the reciprocal vector gk with respect to each other. As many conjugate scans are considered as CBED disks fall into the energy filtered region of the experimental pattern. Electron intensities of the transmitted beam I0 and diffracted beams Igk for all points on conjugate scans are found as a function of crystal thickness t on the basis of the full dynamical calculation.

Computer-Assisted High-Re Solution TEM

1990 ◽  
Vol 48 (1) ◽  
pp. 162-163
Author(s):  
F.A. Ponce ◽  
H. Hikashi
Keyword(s):  
Signal To Noise Ratio ◽  
Accurate Determination ◽  
Computer Software ◽  
Video Camera ◽  
Image Contrast ◽  
Objective Lens ◽  
Computer Assisted ◽  
Optical Parameters ◽  
Astigmatism Correction

The determination of the atomic positions from HRTEM micrographs is only possible if the optical parameters are known to a certain accuracy, and reliable through-focus series are available to match the experimental images with calculated images of possible atomic models. The main limitation in interpreting images at the atomic level is the knowledge of the optical parameters such as beam alignment, astigmatism correction and defocus value. Under ordinary conditions, the uncertainty in these values is sufficiently large to prevent the accurate determination of the atomic positions. Therefore, in order to achieve the resolution power of the microscope (under 0.2nm) it is necessary to take extraordinary measures. The use of on line computers has been proposed [e.g.: 2-5] and used with certain amount of success.We have built a system that can perform operations in the range of one frame stored and analyzed per second. A schematic diagram of the system is shown in figure 1. A JEOL 4000EX microscope equipped with an external computer interface is directly linked to a SUN-3 computer. All electrical parameters in the microscope can be changed via this interface by the use of a set of commands. The image is received from a video camera. A commercial image processor improves the signal-to-noise ratio by recursively averaging with a time constant, usually set at 0.25 sec. The computer software is based on a multi-window system and is entirely mouse-driven. All operations can be performed by clicking the mouse on the appropiate windows and buttons. This capability leads to extreme friendliness, ease of operation, and high operator speeds. Image analysis can be done in various ways. Here, we have measured the image contrast and used it to optimize certain parameters. The system is designed to have instant access to: (a) x- and y- alignment coils, (b) x- and y- astigmatism correction coils, and (c) objective lens current. The algorithm is shown in figure 2. Figure 3 shows an example taken from a thin CdTe crystal. The image contrast is displayed for changing objective lens current (defocus value). The display is calibrated in angstroms. Images are stored on the disk and are accessible by clicking the data points in the graph. Some of the frame-store images are displayed in Fig. 4.

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