Showing papers on "Turbine blade published in 2008"

Evaluation of different turbine concepts for wind power

Abstract: Every year the number of installed wind power plants in the world increases. The horizontal axis wind turbine is the most common type of turbine but there exist other types. Here, three different wind turbines are considered; the horizontal axis wind turbine and two different concepts of vertical axis wind turbines; the Darrieus turbine and the H-rotor. This paper aims at making a comparative study of these three different wind turbines from the most important aspects including structural dynamics, control systems, maintenance, manufacturing and electrical equipment. A case study is presented where three different turbines are compared to each other. Furthermore, a study of blade areas for different turbines is presented. The vertical axis wind turbine appears to be advantageous to the horizontal axis wind turbine in several aspects.

Active load control techniques for wind turbines.

Abstract: This report provides an overview on the current state of wind turbine control and introduces a number of active techniques that could be potentially used for control of wind turbine blades. The focus is on research regarding active flow control (AFC) as it applies to wind turbine performance and loads. The techniques and concepts described here are often described as 'smart structures' or 'smart rotor control'. This field is rapidly growing and there are numerous concepts currently being investigated around the world; some concepts already are focused on the wind energy industry and others are intended for use in other fields, but have the potential for wind turbine control. An AFC system can be broken into three categories: controls and sensors, actuators and devices, and the flow phenomena. This report focuses on the research involved with the actuators and devices and the generated flow phenomena caused by each device.

Behavioral Responses of Bats to Operating Wind Turbines

Abstract: Wind power is one of the fastest growing sectors of the energy industry. Recent studies have reported large numbers of migratory tree-roosting bats being killed at utility-scale wind power facilities, especially in the eastern United States. We used thermal infrared (TIR) cameras to assess the flight behavior of bats at wind turbines because this technology makes it possible to observe the nocturnal behavior of bats and birds independently of supplemental light sources. We conducted this study at the Mountaineer Wind Energy Center in Tucker County, West Virginia, USA, where hundreds of migratory tree bats have been found injured or dead beneath wind turbines. We recorded nightly 9-hour sessions of TIR video of operating turbines from which we assessed altitude, direction, and types of flight maneuvers of bats, birds, and insects. We observed bats actively foraging near operating turbines, rather than simply passing through turbine sites. Our results indicate that bats 1) approached both rotating and nonrotating blades, 2) followed or were trapped in blade-tip vortices, 3) investigated the various parts of the turbine with repeated fly-bys, and 4) were struck directly by rotating blades. Blade rotational speed was a significant negative predictor of collisions with turbine blades, suggesting that bats may be at higher risk of fatality on nights with low wind speeds.

A Review of Current Issues in Lightning Protection of New-Generation Wind-Turbine Blades

Abstract: The salient issues related to lightning protection of long wind-turbine blades are discussed in this paper. We show that the lightning protection of modern wind turbines presents a number of new challenges due to the geometrical, electrical, and mechanical particularities of the turbines. The risk assessment for the lightning-protection-system design is solely based today on downward flashes. We show in this paper that the majority of the strikes to modern turbines are expected to be upward lightning. Neglecting upward flashes, as implicitly done by the International Electrotechnical Commission, might result in an important underestimation of the actual number of strikes to a tall wind turbine. In addition, we show that the rotation of the blades may have a considerable influence on the number of strikes to modern wind turbines as these may be triggering their own lightning. Because wind turbines are tall structures, the lightning currents that are injected by return strokes into the turbines will be affected by reflections at the top, bottom, and junction of the blades with the static base of the turbine. This is of capital importance when calculating the protection of internal circuitry that may be affected by magnetically induced electromotive forces that depend directly on the characteristics of the current in the turbine. The presence of carbon-reinforced plastics (CRP) in the blades introduces a new set of problems to be dealt with in the design of the turbines' lightning protection system. One problem is the mechanical stress resulting from the energy dissipation in CRP laminates due to the circulation of eddy currents. We evaluate in this paper the dissipated energy and propose recommendations as to the number of down conductors and their orientation with respect to the CRP laminates so that the dissipated energy is minimized. It is also emphasized that the high static fields under thunderclouds might have an influence on the moving carbon-fiber parts. This issue needs to be addressed by lightning protection researchers and engineers. Representative full-scale blade tests are still complex because lightning currents from an impulse current generator are conditioned to the electrical characteristics of the element under test and return paths. It is therefore desirable to complement laboratory tests with theoretical and computer modeling for the estimation of fields, currents, and voltages within the blades.

Structural health monitoring of wind turbine blades

Abstract: As electric utility wind turbines increase in size, and correspondingly, increase in initial capital investment cost, there is an increasing need to monitor the health of the structure. Acquiring an early indication of structural or mechanical problems allows operators to better plan for maintenance, possibly operate the machine in a de-rated condition rather than taking the unit off-line, or in the case of an emergency, shut the machine down to avoid further damage. This paper describes several promising structural health monitoring (SHM) techniques that were recently exercised during a fatigue test of a 9 meter glass-epoxy and carbon-epoxy wind turbine blade. The SHM systems were implemented by teams from NASA Kennedy Space Center, Purdue University and Virginia Tech. A commercial off-the-shelf acoustic emission (AE) NDT system gathered blade AE data throughout the test. At a fatigue load cycle rate around 1.2 Hertz, and after more than 4,000,000 fatigue cycles, the blade was diagnostically and visibly failing at the out-board blade spar-cap termination point at 4.5 meters. For safety reasons, the test was stopped just before the blade completely failed. This paper provides an overview of the SHM and NDT system setups and some current test results.

Control of Three-Dimensional Separations in Axial Compressors by Tailored Boundary Layer Suction

Abstract: One of the important ways of improving turbomachinery compressor performance is to control three-dimensional (3D) separations, which form over the suction surface and end wall corner of the blade passage. Based on the insights gained into the formation of these separations, this paper illustrates how an appropriately applied boundary layer suction of up to 0.7% of inlet mass flow can control and eliminate typical compressor stator hub corner 3D separation over a range of operating incidence. The paper describes, using computational fluid dynamics, the application of suction on the blade suction surface and end wall boundary layers and exemplifies the influence of end wall dividing streamline in initiating 3D separation in the blade passage. The removal of the separated region from the blade suction surface is confirmed by an experimental investigation in a compressor cascade involving surface flow visualization, surface static pressure, and exit loss measurements. The ensuing passage flow field is characterized by increased blade loading (static pressure difference between pressure and suction surface), enhanced average static pressure rise, significant loss removal, and a uniform exit flow. This result also enables the contribution of the 3D separation to the overall loss and passage blockage to be assessed.

Robust Multivariable Pitch Control Design for Load Reduction on Large Wind Turbines

Abstract: This paper deals with multivariable pitch control design for wind turbines, including load reducing control objectives. Different design approaches, including collective and cyclic pitch, and robustness aspects are discussed. A control design with decoupled controllers for collective and cyclic pitch is worked out in detail, based on the H ∝ norm minimization approach. The control design is verified by simulations with a full nonlinear model of the wind turbine, showing the potential of multivariable pitch control to actively increase damping of the first axial tower bending mode and to reduce 1p fluctuations in blade root bending moments. Multivariable control design provides a convenient way of including additional load reducing objectives into the pitch controller of wind turbines. Fatigue loading of certain components, as tower and blades, could be reduced significantly.

The Effects of Manufacturing Tolerances on Gas Turbine Cooling

Abstract: This study presents a summary of the effects of manufacturing methods and processing steps upon the resulting thermal boundary conditions for typical highly cooled turbine airfoils. Specific emphasis is placed on the conservatism that must be “designed into” the component for survival due to realistic manufacturing tolerances. Using the features of a typical blade design, the main geometric factors that can influence the blade heat transfer capability through manufacturing variability are enumerated. The tolerances on those geometric factors are provided and the approximate quantitative impact on thermal boundary conditions is summarized. A simple example of airfoil cooling for a representative wall section is used to tabulate the variations with the resulting changes in the most affected thermal boundary conditions. Each of the main geometric factors is then evaluated in terms of its possible effect on maximum metal temperature. Paretos of the effects of manufacturing factors exhibit which factors are key and where tighter tolerances may help. Monte Carlo analysis results show the probability distributions associated with overall cooling changes tied to the tolerances.Copyright © 2008 by ASME

Wind turbine blade

Abstract: A spar ( 30 ) for a wind turbine blade. The spar comprises a plurality (typically three or more) beams ( 33 ) arranged side-by-side. Each beam has a longitudinal web ( 32 ), a flange ( 31 ) at either longitudinal edge. The spar may be made up of a number of modules connected to one another primarily via overlapping shear webs.

Wind turbines, flicker, and photosensitive epilepsy: characterizing the flashing that may precipitate seizures and optimizing guidelines to prevent them.

Abstract: Wind turbines are known to produce shadow flicker by interruption of sunlight by the turbine blades. Known parameters of the seizure provoking effect of flicker, i.e., contrast, frequency, mark-space ratio, retinal area stimulated and percentage of visual cortex involved were applied to wind turbine features. The proportion of patients affected by viewing wind turbines expressed as distance in multiples of the hub height of the turbine showed that seizure risk does not decrease significantly until the distance exceeds 100 times the hub height. Since risk does not diminish with viewing distance, flash frequency is therefore the critical factor and should be kept to a maximum of three per second, i.e., sixty revolutions per minute for a three-bladed turbine. On wind farms the shadows cast by one turbine on another should not be viewable by the public if the cumulative flash rate exceeds three per second. Turbine blades should not be reflective.

Wind turbine monitoring

Abstract: A method of monitoring the performance of a wind turbine (1) uses bending momentdata from strain sensors (4) in the turbine blades (2) to calculate rotational speed of the turbine (1), angular position of the turbine blades (2), drive torque and resultant load on the rotor (3). The method has the advantage that the inputs to the drive train of the wind turbine can be (5) measure directly.

Performance and Internal Flow Characteristics of a Cross-Flow Hydro Turbine by the Shapes of Nozzle and Runner Blade

Abstract: Recently, small hydropower attracts attention because of its clean, renewable and abundant energy resources to develop. Therefore, a cross-flow hydraulic turbine is proposed for small hydropower in this study because the turbine has relatively simple structure and high possibility of applying to small hydropower. The purpose of this study is to investigate the effect of the turbine's structural configuration on the performance and internal flow characteristics of the cross-flow turbine model using CFD analysis. The results show that nozzle shape, runner blade angle and runner blade number are closely related to the performance and internal flow of the turbine. Moreover, air layer in the turbine runner plays very important roles of improving the turbine performance.

Materials Challenges In Present and Future Wind Energy

Abstract: The main concept currently in use in wind energy involves horizontal-axis wind turbines with blades of fiber composite materials. This turbine concept is expected to remain as the major provider of wind power in the foreseeable future. However, turbine sizes are increasing, and installation offshore means that wind turbines will be exposed to more demanding environmental conditions. Many challenges are posed by the use of fiber composites in increasingly large blades and increasingly hostile environments. Among these are achieving adequate stiffness to prevent excessive blade deflection, preventing buckling failure, ensuring adequate fatigue life under variable wind loading combined with gravitational loading, and minimizing the occurrence and consequences of production defects. A major challenge is to develop cost-effective ways to ensure that production defects do not cause unacceptable reductions in equipment strength and lifetime, given that inspection of large wind power structures is often problematic.

Wind turbine blades with vortex generators

Abstract: An advantageous new design of a wind turbine blade and rotor is obtained by providing one, two or more parallel rows of sub-boundary layer vortex generators, whereby a blade is obtained, which is resistant to stall and provides for a high maximum lift coefficient CL,max of the blades and a slender blade design, a low socalled radius specific solidity of the rotor. The very high lift coefficient CL can reduce the necessary blade area and loads or/and increase the length of the blade and maintain the original loads with higher production. The row or rows of sub-boundary layer vortex generators are in a preferred embodiment of the invention provided in combination with Gurney Flaps generating a very high lift coefficient CL with a relative gentle stall at very high angle of attack.

The review of non-destructive testing techniques suitable for inspection of the wind turbine blades

Abstract: Wind power is a promising source of environmentally safe and renewable energy with a high potential. However, in order to fully exploit energy of wind power the construction elements of the wind turbine should be inspected periodically. Wind turbine blades are complicated objects for inspection because they have an arbitrary curved surface, are multi-layered, have variable thickness and are made from anisotropic materials.The presented study covers an overview of the techniques which are used or could be used for on site condition monitoring and effective NDT of wind turbine blades. Inspection methods based on vibration analysis, thermography, X-ray imaging, acoustic emission and ultrasound are reviewed. The objective of this study is review of different NDT techniques, which are used, or could be used for non-destructive testing of wind turbine blades, taking into account the complicated structure of the wind turbine blades as well as possibility to make non-destructive testing in harsh on-site conditions.

Aerostructural Shape Optimization of Wind Turbine Blades Considering Site-Specic Winds

Abstract: The global installed capacity of wind energy has been increasing steadily over the past decade, and the price of electricity derived from it has been continuously declining. While viable siting locations with with high quality wind resources still exist, improved turbine technology and cost reductions can expand the number of locations that are economically viable. This paper investigates the multidisciplinary nature of wind turbine design as it applies to turbine blades. The goal is to reduce the end unit cost of electricity, amortized over the turbine lifetime, for a particular location. A multidisciplinary design feasible (MDF) approach is used for solving the optimization problem. The blade aerostructural analysis couples a quasi-3D aerodynamic analysis | performed using a blade element momentum theory (BEM) method | with a six degree of freedom beam nite element model of the internal spar. Sensitivities for both the aerodynamic and structural analysis are computed using the complex step method. Finally, multipoint optimization of a small 5.0kW xed pitch \urban" wind turbine is performed based on the local wind velocity histograms.

Multiblade Coordinate Transformation and Its Application to Wind Turbine Analysis: Preprint

Abstract: This paper describes the mulitblade coordinate transformation (MBC) modeling process that integrates the dynamics of individual wind turbine blades and expresses them as fixed frames.

Effects of Temperature and Particle Size on Deposition in Land Based Turbines

Abstract: Four series of tests were performed in an accelerated deposition test facility to study the independent effects of particle size, gas temperature, and metal temperature on ash deposits from two candidate power turbine synfuels (coal and petcoke). The facility matches the gas temperature and velocity of modern first stage high pressure turbine vanes while accelerating the deposition process. Particle size was found to have a significant effect on capture efficiency with larger particles causing significant thermal barrier coating (TBC) spallation durin ga4h accelerated test. In the second series of tests, particle deposition rate was found to decrease with decreasing gas temperature. The threshold gas temperature for deposition was approximately 960°C. In the third and fourth test series, impingement cooling was applied to the back side of the target coupon to simulate internal vane cooling. Capture efficiency was reduced with increasing mass flow of coolant air; however, at low levels of cooling, the deposits attached more tenaciously to the TBC layer. Postexposure analyses of the third test series (scanning electron microscopy and X-ray spectroscopy) show decreasing TBC damage with increased cooling levels. DOI: 10.1115/1.2903901

Surface temperature measurement on engine components by means of irreversible thermal coatings

Abstract: Thermal paints are used by most aeronautical manufacturers in dedicated tests to record temperature profiles over the surface of engine components. The analysis of these coatings, which irreversibly change colour with temperature, is at present performed by a skilled operator who draws isothermal lines directly on the components surface. The technique suffers from a lack of accuracy and automation, as only some temperature levels can be determined and there is no convenient means to insert them in a 3D numerical description of the object. This paper first presents the characteristics and implementation of thermal paints. Two major advances are introduced regarding the image processing techniques developed to obtain temperature from colour and the use of a 3D scanner to digitize the outer shape of the components. The analysis is made quicker, more accurate and consistent than the former visual interpretation: temperature information is directly mapped on the 3D mesh and is ready for input in thermal models. The key points of the technique are discussed and illustrated by results on test pieces and turbine blades.

A Smart Wind Turbine Blade Using Distributed Plasma Actuators for Improved Performance

Abstract: This paper presents an innovative Plasma Aerodynamic Control E! ectors (PACE) concept for improved performance of wind turbines. The concept is aimed towards the design of “smart” wind turbine blades with integrated sensor-actuator-controller modules to improve the performance of wind turbines. The system will be designed to enhance energy capture, and reduce aerodynamic loading and noise by way of virtual aerodynamic shaping. Virtual shaping is the modification of the flow field around the surface by means of flow control (plasma actuators), which results in flow changes as if the geometry itself is altered. In e! ect the flow control scheme is giving the designer the capability to change the e! ective pitch distribution across the turbine blade as needed to control blade loading. The present concept is based on the use of surface-mountable, single dielectric barrier discharge (SDBD) plasma actuators on the turbine blades for increased energy capture and noise reduction. The system will allow continuous operation of wind turbines at near optimal conditions (as close as possible to the rated power coe" cient) using a smart/adaptive PACE system in both steady and unsteady conditions (wind gusts, varying wind speeds, etc.), thereby ensuring safety and optimal power capture for electricity conversion. Experimental data and computational model results are presented that show the feasibility of using plasma flow actuators to control the aerodynamic characteristics of selected wind turbine airfoil sections. Two airfoil profiles designed for wind turbine applications were selected for this study. These were the S827 and the S822 profiles. The S827 airfoil was used to examine circulation control to increase the e! ective camber, and leading-edge separation control to increase Clmax. The S822 airfoil was used to demonstrate geometric changes that promote local flow separations that can be manipulated by plasma actuators to control lift. Both these approaches produced controlled changes in the lift coe" cients on the airfoils that were equivalent to a trailing-edge flap or a leading-edge slat, but without conventional moving surfaces.