Articulated wooden blades for a horizontal-axis wind turbine. Design, construction and testing.

A pair of blades were constructed following a Tapered Chord, Zero Twist pattern after Anderson. The construction uses the Wood Epoxy Saturation Technique, with a solid Beech main spar and leading edge joined together with laminated veneers of beech forming a D-section; the trailing edge is formed from millimetre ply skins, foam filled to resist compressive loads. This construction leads to an extremely light, flexible blade, with the centres of gravity and torsion well forward, giving good stability. Each blade has three built-in strain gauges, alowing flapwise bending to be measured. Stiffness, and natural frequencies, were measured, to input to a numerical computer model to calculate blade deformation during operation, and to determine stability boundaries of the blade. Preliminary aerodynamic performance measurements are presented and close agreement is found with theory.

The design, development, and manufacture of large wood/composite wind turbine rotors

Discusses a study conducted to determine the best development path for large wind turbine rotor design. Shape and number of blades, degrees of freedom allowed, and control strategy are considered. Manufacture and costs are also discussed. Two-bladed, stall-regulated, teetered rotors are more cost effective than three-bladed rotors. Single-bladed rotors can be even more cost-effective. No new manufacturing techniques are required. The most cost-effective rotor includes a hub constructed in wood/composite materials, bonded to the blades. There is strong incentive for the blade manufacturer to supply the complete rotor. (from author's abstract)

The use of timber in wind turbines.

The advantages of timber in wind turbine blade construction are discussed, and its properties emphasized. The use of timber/epoxy construction enables a high technical specification to be achieved. Tables are given for specific compressive strengths, fatigue strengths and flexural modulus for wind epoxy and glass reinforced polyester composites. Cost ratios are also discussed for the two materials and the cost advantage for wood is emphasized. (A.J.)

Reynolds number influence on turbulent blocking effects of a rigid plane boundary (2nd report, direct numerical simulation using townsend's eddy forcing)

The Reynolds number influence on turbulent blocking effects by a rigid plane boundary is studied using direct numerical simulation (DNS). A new forcing method using 'simple model eddies' (Townsend 1976) for DNS of stationary homogeneous isotropic turbulence is proposed. A force field is obtained in real space by sprinkling many space-filling 'simple model eddies' whose centers are randomly but uniformly distributed in space and whose axes of rotation are random. The method is applied to a shear-free turbulent boundary layer over a rigid plane boundary and the blocking effects are investigated. The results show that stationary homogeneous isotropic turbulence is generated in real space using the present method. By using different model eddies with different sizes and rotation speeds, we could change the turbulence properties such as the integral and micro scales, the turbulent Reynolds number and the isotropy of turbulence. Turbulence intensities near the wall showed good agreements with the previous measurement and the linear analysis based on a rapid distortion theory (RDT). The splat effect (i.e., turbulence intensities of the components parallel to the boundary are amplified) occurs near the boundary and the viscous effect prohibits the splat effect at the quasi steady state at low Reynolds number.

Optimizing the energy output of vertical axis wind turbines for fluctuating wind conditions

The control of a wind turbine to the mean wind speed in a gusty wind results in very poor performance. Fluctuations in wind speed with time constants shorter than the response time of a wind turbine results in operation away from optimum design conditions. The effectiveness of a turbine operating in a gusty wind is shown though the use of an unsteady performance coefficient, C e. This performance coefficient is similar in form to a power coefficient. However in order to accommodate unsteady effects, Ce is defined as a ratio of energy extracted to the total wind energy available over a set time period. The turbine's response to real wind data is modelled, in the first instance, by assuming a constant rotational speed operation. It is shown that a significant increase in energy production can be realized by demanding a Tip Speed Ratio above the steady state optimum. The constant speed model is then further extended to incorporate inertial and controller effects. Parameters dictating how well a turbine can track a demand in Tip Speed Ratio have been identified and combined, to form a non-dimensional turbine response parameter. This parameter characterizes a turbine's ability to track a demand in Tip Speed Ratio dependent on an effective gust frequency. A significant increase in energy output of 42% and 245% is illustrated through the application of this over-speed control. This is for the constant rotational speed and Tip Speed Ratio feedback models respectively. The affect of airfoil choice on energy extraction within a gusty wind has been considered. The adaptive control logic developed enables the application of airfoils demonstrating high maximum L/D values but sharp stalling characteristics to be successfully used in a VAWT design.

The BDFM as a generator in wind turbines

The Brushless Doubly-Fed Machine (BDFM) is attractive for use in wind turbines, especially offshore, as it offers high reliability by virtue of the absence of brushgear. Critical issues in the use of the BDFM in this role at a system level include the appropriate mode of operation, the sizing of associated converter and the control of the machine. At a machine level, the design of the machine and the determination of its ratings are important. Both system and machine issues are reviewed in the light of recent advances in the study of the BDFM, and preliminary comparisons are made with the well-established doubly fed wound rotor induction generator. © 2006 IEEE.

Minimize frequency fluctuations of isolated power system with wind farm by using superconducting magnetic energy storage

Wind power generation as one of the most popular renewable energy applications is absorbing more and more attention all over the world. However, output power fluctuations of wind farm due to random variations of wind speed can cause network frequency and voltage flicker in power systems. The power quality consequently declines, particularly in an isolated power system such as the power system in a remote community or a small island. This paper proposes an application of superconducting magnetic energy storage (SMES) to minimize output fluctuations of an isolated power system with wind farm. The isolated power system is fed by a diesel generator and a wind generator consisting of a wind turbine and squirrel cage induction machine. The control strategy is detailed and the proposed system is evaluated by simulation in Matlab/Simulink.

A policy dimension required for technology roadmapping: Learning from the development of emerging wind energy industry in China

Innovation policies play an important role throughout the development process of emerging industries. However, existing policy studies view the process as a black-box, and fail to understand the policy-industry interactions through the process. This paper aims to develop an integrated technology roadmapping tool, in order to facilitate the better understanding of policy heterogeneity at the different stages of new energy industries in China. Through the case study of Chinese wind energy equipment manufacturing industry, this paper elaborates the dynamics between policy and the growth process of the industry. Further, this paper generalizes some Chinese specifics for the policy-industry interactions. As a practical output, this study proposes a policy-technology roadmapping framework that maps policy-market-product- technology interactions in response to the requirement for analyzing and planning the development of new industries in emerging economies (e.g. China). This paper will be of interest to policy makers, strategists, investors, and industrial experts. © 2011 IEEE.

A dynamic model to predict the occurrence of skidding in wind-turbine bearings

Despite use of the best in current design practices, high-speed shaft (HSS) bearings, in a wind-turbine gearbox, continue to exhibit a high rate of premature failure. As HSS bearings operate under low loads and high speeds, these bearings are prone to skidding. However, most of the existing methods for analyzing skidding are quasi-static in nature and cannot be used to study dynamic operating conditions. This paper proposes a dynamic model, which includes gyroscopic and centrifugal effects, to study the skidding characteristics of angular-contact ball-bearings. Traction forces between rolling-elements and raceways are obtained using elastohydrodynamic (EHD) lubrication theory. Underlying gross-sliding mechanisms for pure axial loads, and combined radial and axial loads are also studied. The proposed model will enable engineers to improve bearing reliability at the design stage, by estimating the amount of skidding. © 2011 Published under licence by IOP Publishing Ltd.