Showing papers on "Turbine blade published in 2010"

Wind Turbine Technology

Abstract: Chronological History of Wind Turbine Technology Major Benefits and Problems Associated with Alternate Energy Sources Benefits and Disadvantages of Wind Turbine Technology Worldwide Utilization of Wind Turbines Operating Principles of Wind Turbines Wind Turbine Classifications Wind Farm Developers Design Configurations Next Generation Wind Turbines with Unique Features Typical Wind Power Estimates for United States Design Aspects and Performance Requirements Types of Wind Turbines Modern Wind Turbines Off-Design Performance Techniques for Capturing Large Amounts of Wind Energy Annual Energy Acquisition from Specified Wind Turbine Site Estimating Annual Hours of Capturing Wind Energy Design Aspects and Performance Capabilities of Wind Turbine Rotors One-Dimensional Theory for Ideal Rotor Two-Dimensional Aerodynamic Model Three-Dimensional Aerodynamic Model for Wing of Finite Length Rotor Design Requirements for Wind Farm Applications Hydrodynamic Analysis of Flow over Rotor Wind Turbine Blade Design Requirements Analysis of Performance of Propeller Blades Blade Performance Application of Beam Theory to Various Turbine Blade Configurations Material Requirements for Blades Critical Features of Blade Section Sensors and Control Devices Required for Dynamic Stability and Improved Performance under Variable Wind Environments Regulation Control Systems Sensors for Monitoring Wind Parameters Transmission Systems Electrical Generators Performance Capabilities and Limitations of Synchronous Generators Critical Rotor Performance Parameters Impacts of Airfoil Characteristics on Blade and Turbine Performance Automatic Shut-Down Capability Critical Design Aspects of HAWT and VAWT Rotors Low Harmonic Content Electrical Generators for Improving Efficiency Impacts of Loadings on Structural Integrity of Wind Turbine Stand-Alone Wind Turbine Systems Historical Background: Use at Remote Sites Configurations of Stand-Alone Systems Stand-Alone Systems for Remote Sites Sizing of System Components Stand-Alone Systems with Utility Power Back-Up Stand-Alone Wind TurbineBased Systems for Various Applications Hybrid Systems for Village Electrification Multitasking Wind Turbines Wind Energy Conversion Techniques in Built Environments Concentrator Configuration Requirements Energy Design Buildings Local Wind Characteristics in Built Environments Impact of Built Environment on BAWT Performance Environmental Issues and Economic Factors Affecting Wind Turbine Installation Environmental Factors and Other Critical Issues Problems Arising from Large Windstream Diameters Estimating Critical Performance Parameters Using Classical BEM Theory Justification of Wind Turbine Installation Based on Economics Estimated Costs of Critical Components and Subsystems Wind Turbine Towers Index Each chapter begins with an Introduction and concludes with a Summary and References.

Effects of Thermal Stability and Incoming Boundary-Layer Flow Characteristics on Wind-Turbine Wakes: A Wind-Tunnel Study

Abstract: Wind-tunnel experiments were carried out to study turbulence statistics in the wake of a model wind turbine placed in a boundary-layer flow under both neutral and stably stratified conditions. High-resolution velocity and temperature measurements, obtained using a customized triple wire (cross-wire and cold wire) anemometer, were used to characterize the mean velocity, turbulence intensity, turbulent fluxes, and spectra at different locations in the wake. The effect of the wake on the turbulence statistics is found to extend as far as 20 rotor diameters downwind of the turbine. The velocity deficit has a nearly axisymmetric shape, which can be approximated by a Gaussian distribution and a power-law decay with distance. This decay in the near-wake region is found to be faster in the stable case. Turbulence intensity distribution is clearly non-axisymmetric due to the non-uniform distribution of the incoming velocity in the boundary layer. In the neutral case, the maximum turbulence intensity is located above the hub height, around the rotor tip location and at a distance of about 4–5.5 rotor diameters, which are common separations between wind turbines in wind farms. The enhancement of turbulence intensity is associated with strong shear and turbulent kinetic energy production in that region. In the stable case, the stronger shear in the incoming flow leads to a slightly stronger and larger region of enhanced turbulence intensity, which extends between 3 and 6 rotor diameters downwind of the turbine location. Power spectra of the streamwise and vertical velocities show a strong signature of the turbine blade tip vortices at the top tip height up to a distance of about 1–2 rotor diameters. This spectral signature is stronger in the vertical velocity component. At longer downwind distances, tip vortices are not evident and the von Karman formulation agrees well with the measured velocity spectra.

Turbine blade film cooling using psp technique

Abstract: Film cooling is widely used to protect modern gas turbine blades and vanes from the ever increasing inlet temperatures. Film cooling involves a very complex turbulent flow-field, the characterization of which is necessary for reliable and economical design. Several experimental studies have focused on gas turbine blade, vane and end-wall film cooling over the past few decades. Measurements of heat transfer coefficients, film cooling effectiveness values and heat flux ratios using several different experimental methods have been reported. The emphasis of this current review is on the Pressure Sensitive Paint (PSP) mass transfer analogy to determine the film cooling effectiveness. The theoretical basis of the method is presented in detail. Important results in the open literature obtained using the PSP method are presented, discussing parametric effects of blowing ratio, momentum ratio, density ratio, hole shape, surface geometry, free-stream turbulence on flat plates, turbine blades, vanes and end-walls. The PSP method provides very high resolution contours of film cooling effectiveness, without being subject to the conduction error in high thermal gradient regions near the hole.

Large Eddy Simulations of large wind-turbine arrays in the atmospheric boundary layer

Abstract: Large Eddy Simulations (LES) of arrays of wind turbines in the atmospheric turbulent boundary layer with many turbines often require simplifled models for the efiects of individual turbines, in order to avoid having to use very flne grid spacings near the individual (moving) turbine blades. This goal can be accomplished using the actuator disk model. This approach, however, raises several issues when implemented in the context of LES. In particular, the question is raised of which reference velocity should be used when parameterizing the induced forces: instantaneous versus time averaged, undisturbed velocity or the local one. Also, one may consider including tangential forces to represent the angular momentum in the wakes. In this paper we present several arguments to make the appropriate choices, and illustrate the efiects of these choices in LES of two wind turbine arrays, one with an aligned and one with a staggered arrangement. Predicted power outputs, as well as features of the predicted ∞ow flelds are analyzed.

An overview of active load control techniques for wind turbines with an emphasis on microtabs

Abstract: This paper outlines the benefits and challenges of utilizing active flow control (AFC) for wind turbines. The goal of AFC is to mitigate damaging loads and control the aeroelastic response of wind turbine blades. This can be accomplished by sensing changes in turbine operation and activating devices to adjust the sectional lift coefficient and/or local angle of attack. Fifteen AFC devices are introduced, and four are described in more detail. Non-traditional trailing-edge flaps, plasma actuators, vortex generator jets and microtabs are examples of devices that hold promise for wind turbine control. The microtab system is discussed in further detail including recent experimental results demonstrating its effectiveness in a three-dimensional environment. Wind tunnel tests indicated that a nearly constant change in CL over a wide range of angles of attack is possible with microtab control. Using an angle of attack of 5 degrees as a reference, microtabs with a height of 1.5%c were capable of increasing CL by +0.21 (37%) and decreasing CL by −0.23 (−40%). The results are consistent with findings from past two-dimensional experiments and numerical efforts. Through comparisons to other load control studies, the controllable range of this microtab system is determined to be suitable for smart blade applications. Copyright © 2009 John Wiley & Sons, Ltd.

Structural collapse of a wind turbine blade. Part A: Static test and equivalent single layered models

Abstract: The overall objective is a top-down approach to structural instability phenomena in wind turbine blades, which is used to identify the physics governing the ultimate strength of a generic wind turbine blade under a flap-wise static test. The work is concerned with the actual testing and the adoption of a phenomenological approach, and a discussion is conducted to assess and evaluate the wind turbine blade response during loading and after collapse by correlating experimental findings with numerical model predictions. The ultimate strength of the blade studied is governed by instability phenomena in the form of delamination and buckling. Interaction between both instability phenomena occurs causing a progressive collapse of the blade structure.

An Extended Pattern Search Approach to Wind Farm Layout Optimization

Abstract: An extended pattern search approach is presented for the optimization of the placement of wind turbines on a wind farm. Problem-specific extensions infuse stochastic characteristics into the deterministic pattern search, inhibiting convergence on local optima and yielding better results than pattern search alone. The optimal layout for a wind farm is considered here to be one that maximizes the power generation of the farm while minimizing the farm cost. To estimate the power output, an established wake model is used to account for the aerodynamic effects of turbine blades on downstream wind speed, as the oncoming wind speed for any turbine is proportional to the amount of power the turbine can produce. As turbines on a wind farm are in close proximity, the interaction of turbulent wakes developed by the turbines can have a significant effect on the power development capability of the farm. The farm cost is estimated using an accepted simplified model that is a function of the number of turbines. The algorithm develops a two-dimensional layout for a given number of turbines, performing local turbine movement while applying global evaluation. Three test cases are presented: (a) constant, unidirectional wind, (b) constant, multidirectional wind, and (c) varying, multidirectional wind. The purpose of this work is to explore the ability of an extended pattern search (EPS) algorithm to solve the wind farm layout problem, as EPS has been shown to be particularly effective in solving multimodal layout problems. It is also intended to show that the inclusion of extensions into the algorithm can better inform the search than algorithms that have been previously presented in the literature. Resulting layouts created by this extended pattern search algorithm develop more power than previously explored algorithms using the same evaluation models and objective functions. In addition, the algorithm’s resulting layouts motivate a heuristic that aids in the manual development of the best layout found to date. The results of this work validate the application of an extended pattern search algorithm to the wind farm layout problem, and that its performance is enhanced by the use of problem-specific extensions that aid in developing results that are superior to those developed by previous algorithms.

Deformable trailing edge flaps for modern megawatt wind turbine controllers using strain gauge sensors

Abstract: The present work contains a deformable trailing edge flap controller integrated in a numerically simulated modern, variablespeed, pitch-regulated megawatt (MW)-size wind turbine. The aeroservoelastic multi-body code HAWC2 acts as a component in the control loop design. At the core of the proposed controller, all unsteady loads are divided by frequency content. Blade pitching and generator moment react to low-frequency excitations, whereas flaps deal with high-frequency excitations. The present work should be regarded as an investigation into the fatigue load reduction potential when applying trailing edge flaps on a wind turbine blade rather than a conclusive control design with traditional issues like stability and robustness fully investigated. Recent works have shown that the fatigue load reduction by use of trailing edge flaps may be greater than for traditional pitch control methods. By enabling the trailing edge to move independently and quickly along the spanwise position of the blade, local small flutuations in the aerodynamic forces can be alleviated by deformation of the airfoil flap. Strain gauges are used as input for the flap controller, and the effect of placing strain gauges at various radial positions on the blade is investigated. An optimization routine minimizes blade root fatigue loads. Calculations are based on the 5 MW reference wind turbine part of the UpWind project primarily with a mean turbulent wind speed close to rated power. A fatigue load reduction of 25% in the blade root moment was obtained for a continuous 6.3 m long flap. Copyright © 2009 John Wiley & Sons, Ltd.

Gas Turbine Blade Tip Heat Transfer and Cooling: A Literature Survey

Abstract: Gas turbines are widely used for aircraft propulsion, land-base power generation, and other industrial applications like trains, marines, automobiles, etc. To satisfy the fast development of advanced gas turbines, the operating temperature must be increased to improve the thermal efficiency and output work of the gas turbine engine. However, the heat transferred to the turbine blade is substantially increased as the turbine inlet temperature is continuously increased. Thus, it is very important to cool the turbine blades for a long durability and safe operation. Cooling the blade must include cooling of the key regions being exposed to the hot gas. The blade tip region is such a critical area and is indeed difficult to cool. This results from the tip clearance gap where the complex tip leakage flow occurs and thereby local high heat loads prevail. This paper presents a literature survey of blade tip leakage flow and heat transfer, as well as research of external and internal cooling technologies. The pres...

Weather response to a large wind turbine array

Abstract: . Electrical generation by wind turbines is increasing rapidly, and has been projected to satisfy 15% of world electric demand by 2030. The extensive installation of wind farms would alter surface roughness and significantly impact the atmospheric circulation due to the additional surface roughness forcing. This forcing could be changed deliberately by adjusting the attitude of the turbine blades with respect to the wind, which would enable the "management" of a large array of wind turbines. Using a General Circulation Model (GCM), we represent a continent-scale wind farm as a distributed array of surface roughness elements. Here we show that initial disturbances caused by a step change in roughness grow within four and a half days such that the flow is altered at synoptic scales. The growth rate of the induced perturbations is largest in regions of high atmospheric instability. For a roughness change imposed over North America, the induced perturbations involve substantial changes in the track and development of cyclones over the North Atlantic, and the magnitude of the perturbations rises above the level of forecast uncertainty.

Structural collapse of a wind turbine blade. Part B: Progressive interlaminar failure models

Abstract: The objective of this paper is to present a geometrical nonlinear and interlaminar progressive failure finite element analysis of a generic wind turbine blade undergoing a static flap-wise load and comparisons with experimental findings. It is found that the predictive numerical models show excellent correlation with the experimental findings and observations in the pre-instability response. Consequently, the ultimate strength of the wind turbine blade studied is governed by a delamination and buckling coupled phenomenon, which results in a chain of events and sudden structural collapse with compressive fibre failure in the delaminated flange material. Finally, a parametric study of the critical load factors with respect to various delamination sizes and positions inside the compressive flange of the wind turbine blade is presented.

Effect of Blade Inclination Angle on a Darrieus Wind Turbine

Abstract: This paper presents a model for the evaluation of energy performance and aerodynamic forces acting on a small helical Darrieus vertical axis wind turbine depending on blade inclination angle. It consists of an analytical code coupled to a solid modeling software capable of generating the desired blade geometry depending on the desired design geometric parameters, which is linked to a finite volume CFD code for the calculation of rotor performance. After describing and validating the model with experimental data, the results of numerical simulations are proposed on the bases of five machine architectures, which are characterized by an inclination of the blades with respect to the horizontal plane in order to generate a phase shift angle between lower and upper blade sections of 0 deg, 30 deg, 60 deg, 90 deg, and 120 deg for a rotor having an aspect ratio of 1.5. The effects of blade inclination on tangential and axial forces are first discussed and then the overall rotor torque is considered as a function of azimuthal position of the blades. Finally, the downstream tip recirculation zone due to the finite blade extension is analyzed for each blade inclination angle, achieving a numerical quantification of the influence of induced drag on rotor performance, as a function of both blade element longitudinal and azimuthal positions of the blade itself.

Multidisciplinary Design Optimization for Glass-Fiber Epoxy-Matrix Composite 5 MW Horizontal-Axis Wind-Turbine Blades

Abstract: A multi-disciplinary design-optimization procedure has been introduced and used for the development of cost-effective glass-fiber reinforced epoxy-matrix composite 5 MW horizontal-axis wind-turbine (HAWT) blades The turbine-blade cost-effectiveness has been defined using the cost of energy (CoE), ie, a ratio of the three-blade HAWT rotor development/fabrication cost and the associated annual energy production To assess the annual energy production as a function of the blade design and operating conditions, an aerodynamics-based computational analysis had to be employed As far as the turbine blade cost is concerned, it is assessed for a given aerodynamic design by separately computing the blade mass and the associated blade-mass/size-dependent production cost For each aerodynamic design analyzed, a structural finite element-based and a post-processing life-cycle assessment analyses were employed in order to determine a minimal blade mass which ensures that the functional requirements pertaining to the quasi-static strength of the blade, fatigue-controlled blade durability and blade stiffness are satisfied To determine the turbine-blade production cost (for the currently prevailing fabrication process, the wet lay-up) available data regarding the industry manufacturing experience were combined with the attendant blade mass, surface area, and the duration of the assumed production run The work clearly revealed the challenges associated with simultaneously satisfying the strength, durability and stiffness requirements while maintaining a high level of wind-energy capture efficiency and a lower production cost

Active control of flow separation and structural vibrations of wind turbine blades

Abstract: The feasibility of using synthetic jet actuators to enhance the performance of wind turbine blades was explored in wind tunnel experiments on a small scale model blade. Using this technique, the global flow field over the blade was altered such that flow separation was mitigated. Consequently, this resulted in a significant decrease in the vibration of the blade. Global flow measurements were conducted, where the moments and forces on the blade were measured using a six component wall-mounted load cell. The effect of the actuation was also examined on the surface static pressure at two spanwise locations; near the blade's root and near its tip. In addition, Particle Image Velocimetry (PIV) technique was used to quantify the flow field over the blade. Using synthetic jets, the flow over the blade was either fully or partially reattached, depending on the angle of attack, and the Reynolds number. Furthermore, the changes induced on the moments and forces, as well as on the blade vibrations were found to be proportionally controllable by either changing the momentum coefficient, the number of synthetic jets used, or by the driving waveform. Finally, a proof-of-concept closed-loop control system was developed to test the ability of using synthetic jet actuators to restore and maintain flow attachment and reduce the vibrations in the blade during dynamic pitching maneuvers. The control system demonstrated the ability of synthetic jet actuators to reduce blade vibrations during dynamic motion depending upon their control concept, which might be either pitch or active stall control. Copyright © 2009 John Wiley & Sons, Ltd.

Protected wind turbine blade, a method of manufacturing it and a wind turbine

Abstract: A protected turbine blade includes a first turbine blade shell and a second turbine blade shell, being fiber-reinforced, are connected by a cured resin and provided with a protective cover at a leading edge. The protective cover is a composite comprising a layer of UV-resistant thermoplastic material and a layer of cured epoxy resin, the UV-resistant thermoplastic material having the following properties a surface free energy of less than 35 mJ/m2, and a erosion resistance of the thermoplastic material larger than the erosion resistance of the cured resin connecting the turbine blade shells. The layer of cured epoxy-resin covers the cured resin over at least part of the length of the distal half of the turbine blade, and is bonded to said turbine blade. A method of manufacturing such a turbine blade, and to a turbine having such turbine blades is also provided.

Wetting and interactions of Ni- and Co-based superalloys with different ceramic materials

Abstract: In this work, a systematic study of the wetting behavior of two Ni-based and one Co-based superalloys, used, in particular, for the fabrication of turbine blades, is presented with reference to different ceramic substrates: sapphire, polycrystalline alumina, zirconia, and mullite. Wettability tests have been performed by means of the “sessile drop” method at 1500 °C; the characterization of the interfaces between the molten drop and the substrates has been performed by SEM/EDS analysis in order to check the final characteristics of the solidified interfaces. The results are discussed in terms of chemical interactions in relation to the processing parameters and as a function of the surface and interfacial, morphological and energetic properties of the systems.

Blade Pitch Control with Preview Wind Measurements y

Abstract: Light detection and ranging systems are able to measure conditions at a distance in front of wind turbines and are therefore suited to providing preview information of wind disturbances before they impact the turbine blades. In this study, preview-based disturbance feedforward control is investigated for load mitigation both with and without the use of multi-blade coordinate based controllers. Performance is evaluated assuming highly idealized wind measurements that rotate with the blades and more realistic stationary measurements. The results obtained using idealized, \best case" measurements show that excellent performance gains are possible with reasonable pitch rates. However, the results using more realistic wind measurements show that without further optimization of the controller and/or better processing of measurements, errors in determining the shear local to each blade can remove any advantage obtained by using preview-based feedforward techniques.

Segmented wind turbine blades

Abstract: A rotor blade (10) for a wind turbine includes a plurality of individual blade segments (12), with each blade segment defining an internal passage (22) extending between the longitudinal ends of the blade segment. A rigid spar member (28) extends longitudinally through the internal passages of the individual blade segments such that the blade segments are aligned and connected end-to-end on said spar member to define a complete rotor blade (10). The spar member has a cross-sectional profile that is keyed to the cross-sectional profile of the internal passage in the blade segments. The spar member includes oppositely facing spar caps (34,36) that engage against the inside surfaces of the blade segments within the internal passages.

Unsteady Separation Control on Wind Turbine Blades using Fluidic Oscillators

Abstract: Fluidic oscillators are actuators that are essentially constituted of a flow vane with no moving parts. They are very effective in generating an oscillating velocity field, and because of their robustness and potential to meet most application requirements they have been thoroughly investigated in previous years. In this work fluidic oscillators have been embedded in an airfoil representative of the outboard sections of wind turbine blades, and subsequently tested at full-scale Reynolds numbers 2.0·10 6 ≤ Re ≤ 4.8·10 6 in the laminar wind tunnel at the University of Stuttgart. The effects of the unsteady actuation on the lift and drag strongly depend upon Re, the level of actuation, and the state of the airfoil surface. However, strong improvements have been obtained throughout the whole testing envelope, with relative lift increase spanning from a minimum of 10 to over 60% and substantial stall margin extension. In addition, employing fluidic oscillators strongly reduces the suction surface boundary-layer thickness and the unsteadiness of the mean flow velocity.

Pulsed eddy current thermography: System development and evaluation

Abstract: There is a need for fast and efficient techniques to inspect engineering structures and complex components such as aircraft turbine blades to identify potential sites of failure. Pulsed eddy current (PEC) thermography is a new inspection technique which allows the user to capture the eddy current distribution in a component or structure using infrared imaging and detect defects over a relatively wide area. The technique is applicable to materials with a reasonable level of electrical conductivity and has the ability to detect defects under coatings. However, PEC thermography has received relatively little attention compared to other thermographic inspection techniques. In this paper, the design, development and optimisation of a PEC thermography inspection system is detailed, including coil design for global and local heating of samples, optimisation of excitation parameters (frequency, power, pulse duration etc) and camera selection. The system is used to inspect several real-world samples, using different coil designs, and the results are assessed using newly developed feature extraction techniques. The work shows that with judicious coil design and selection of excitation parameters, PEC thermography can be used to obtain quantitative information for defect characterisation through analysis of the surface heating pattern and the transient temperature change.

Trailing Edge Film Cooling of Gas Turbine Airfoils: External Cooling Performance of Various Internal Pin Fin Configurations

Abstract: The present paper describes an experimental study on trailing edge film cooling of modern high-pressure turbine blades using coolant ejection through planar slots on a pressure side cutback. The experimental test section consists of a generic scaled-up trailing edge model in an atmospheric open loop wind tunnel, which has been used in earlier studies by Martini et al. (e.g. [1]). An infrared thermographic measurement technique is employed, which allows for the application of engine-realistic density ratios around 1.6 by increasing the main flow temperature. The effects of different geometric configurations on the structure and performance of the cooling film are investigated in terms of film cooling effectiveness, heat transfer, and discharge behavior. Among other issues, the interaction between internal turbulators, namely an array of pin fins, with the ejection slot lip is of major interest. Therefore, different designs of the coolant ejection lip are studied. Four different ratios of lip thickness to ejection slot height (t/H = 0.2, 0.5, 1.0, 1.5) are investigated as well as three different lip profiles representing typical manufacturing imperfections and wear. Other geometric variations comprise elliptic pin fins with spanwise and streamwise orientation and the application of land extensions from the internal coolant cavity onto the cut-back surface. The blowing ratio is varied between 0.2 < M < 1.25. In terms of film cooling effectiveness the results show a strong dependency on ejection lip thickness and minor improvements are obtained with a rounded ejection lip profile. Significant improvements are achieved using land extensions. The elliptic pin fins have a strong effect on discharge behavior as well as on film cooling effectiveness and heat transfer. Except for the elliptic pin fins, the geometric variations have only a minor influence on heat transfer.Copyright © 2010 by ASME