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1
Nygard, Øyvind Vik. "Wake behind a horizontal-axis wind turbine." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13691.
Full textAbstract:
In this paper theory on cylinder and wind turbine wakes have been studied, and experimental work on the wake behind a wind turbine have been carried out in the Fluids engineering laboratory at NTNU.The objective of this paper is to show and explain how the wake from the tower of a wind turbine develops and interacts with the rotor wake. It is desirable to study the wake for different operating conditions of the wind turbine to see how the wake development is affected. A summary of classical wake theory, aerodynamics and wind turbine wakes will be given. Measurements in the wake of a cylinder fitted with pressure taps for drag calculation will be compared to theory and used as a reference. Also, the wake behind the wind turbine tower with the blades taken off will be studied and compared to the tower wake found behind the operating wind turbine.For comparison, reference measurements were done in the wake behind a cylinder and behind the free standing wind turbine tower without blades. The drag coefficient obtained from pressure measurements on the cylinder surface were 1.077 and match the expected value of 1.2 fairly well. However, neither the shape nor the maximum velocity deficit measured in the wake fit the theoretical profile. Drag coefficients calculated from the momentum deficit across the wake were only in the range of 0.65, which is almost half of the expected, and the huge deviation from theory could not be explained. With values between 1.07 and 1.50 the measured drag coefficients in the wake of the tower alone were also not consistent with theory. The shape of the tower wake profile coincides better with theory than the cylinder wake, but the maximum velocity deficit is generally lower than predicted by theory. Difference in drag can be explained with blockage effect and the smaller velocity deficit may be attributed to the free stream flow over the top of the tower interfering with the wake downstream of the tower.Wake surveys behind the wind turbine were done at three operating conditions: Optimum tip speed ratio; low tip speed ratio, with power output half of output at best point operation; and high tip speed ratio, with power output half of output at best point operation. The increased turbulence level behind the rotor the flow seen by the tower is believed to creates a turbulent boundary layer which stays attached to the surface to a point further back on the tower, creating a narrower and weaker wake compared the free standing tower wake. Optimum turbine operation gives a stronger rotation of the wake doe to the higher torque on the blades compared to the two other cases. At high TSR the wake is more uniform, and the tower wake disappears faster than in the wake of the turbine operating at lower TSR. The Strouhal number found in all the wakes match well with theory and does not seem to be affected by the rotor wake except that the tower vortices dies out quicker.
2
Hankin, David. "Wake impacting on a horizontal axis wind turbine." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/24565.
Full textAbstract:
Offshore wind is set to contribute a significant portion of the UK's renewable energy production. In order to achieve this, installation costs must be reduced and energy density optimised, but this must be balanced with the increase in maintenance costs resulting from fatigue due to wake impact. The aim of this thesis is to investigate the effects of horizontal axis wind turbine wake impact on a downstream rotor. A force-free wake implementation of the unsteady vortex lattice method has been developed in order to simulate the flow around the downstream rotor, including the effects of an upstream rotor wake, uncorrelated wind field and the dynamic inflow response of the turbine wake. In addition, a series of wind tunnel experiments were undertaken to characterise the wake of a horizontal axis wind turbine and measure time histories of the turbine thrust and blade root bending moments in uniform and turbulent inflow and upstream rotor wake impact. Comparisons are made between the model and wind tunnel experiments for a range of flow cases: uniform inflow, turbulent inflow and operation in an upstream rotor wake at varying degrees of lateral offset. The upstream flow field is modelled on a Cartesian grid, following the assumption of frozen turbulence. For both the turbulent flow and upstream rotor wake, a simplified model is used as a starting point and then refined to better model the effect of turbulence. Ambient turbulence is found to have minimal impact on the mean response of the rotor, suggesting that a linearised approach can be taken in the numerical modelling of turbulence effects. The simple model better predicts the low frequency response, but does not capture the per revolution frequencies identified by the refined model, which also better predicts the admittance. The response of the rotor to an aligned upstream rotor wake is found to be dominated by the wake turbulence, although the proposed model does not reproduce the measured response. However, for laterally offset upstream rotor wakes the mean velocity deficit is the dominant factor and the model captures the response, including the shift to higher bending moment cycles which will contribute to increased fatigue.
3
Al-Khudairi, Othman. "Structural performance of horizontal axis wind turbine blade." Thesis, Kingston University, 2014. http://eprints.kingston.ac.uk/32197/.
Full textAbstract:
The power output from a wind turbine is proportional to rotor swept area and as a result in the past 30 years continuous effort has been made to design larger blades. In this period, the blade length has been increased about 10 times since 1980s to present time. With the longest blade currently measuring more than 100m in length, wind turbine blade designers and manufacturers face enormous challenges to encounter the effect of increased weight and other loads on fatigue durability of the blade. Wind turbine blades are mainly made from glass fibre reinforced plastic (GFRP) composite. materials. As a result, in the design of various parts of wind turbine blades such as the shear web, spar cap and the aerofoil the fatigue behaviour of F RP materials is required. The performance of these parts as well as the adhesively bonded joint under fatigue loading is crucial for structural integrity of a long lasting blade. During operation, delamination can initiate and propagate shortening blade life; hence, characterisation of failure envelope of GFRP laminates under different loading mode is necessary. In this regard in this project, quasi-static tests were carried out to find mode 1, mode 11 and mixed mode I/11 delamination fracture toughness using DCB, ENF and MMB tests and the fracture envelope was established for various mode mixity. In the next stage, the stress-lifetime (S-N) diagrams of the GFRP was studied. Fatigue-life experiments on three different types of loading, i.e. tension-tension at R=0.1, 0.5, tension- compression at R=-1 and compression-compression at R=2 and R=10 were performed. From the results of S-N diagrams, the constant life diagrams (CLD) for 90 degree and 0 degree fibre directions were constructed. CLD diagrams are useful for prediction of fatigue lifetime for loading condition that no experimental data available. The analysis of delamination crack propagation under cyclic loading was next area of the research. The onset life and propagation delamination crack grth of 0//0 interface of GR P laminate in mode I loading using DCB specimens was investigated and the Gm. from the onset life test was determined. From the fitted curve to mode I experimental propagation data the Paris’ law coefficient for the laminated GFRP in mode I was determined. The mode II fatigue crack growth in laminated 0//0 GFRP material was also investigated using ENF specimens. The fatigue behaviour in this mode is analysed based on application of Paris’ law as a function of energy release rate for mode II loading. From the fitted curve to experimental data, the Paris’ law coefficient for the laminated GFRP in mode II was determined. The effect of fatigue delamination growth on fracture surface was studied by fractography analysis of SEM images of fracture surfaces. Studying the behaviour of GFRP under cyclic loading and delamination under static and dynamic load led to full-scale testing of wind turbine blade to establish damage tolerance of the blade under cyclic loading. The sensitivity of wind turbine blade to damage has considerable interest for turbine operators and manufacturers. For full-scale fatigue testing, calibration test and modal analysis of a 45.7m blade has been done and moment-strain diagram and natural frequencies of the blade were obtained. Next, the blade sensitivity to damage under fatigue loading was investigated. The blade has been damaged intentionally by initially inserting a crack of 0.2m between the shear web and spar cap and later it was extended to 1m. The effect of these damages on the modal shape, natural frequencies and strains at various locations of the blade were investigated. The damaged blade fatigue tested, the structural integrity and growth of damage were monitored, and the results were discussed. Finally for the improvement of delamination resistance for joints between spar beam and aero-shell stitching method was used. T-beam and box beam joint were chosen as the platform for testing the stitching effect on the delamination. Various pattern of stitching was applied and the optimum pattern was determined.
4
Gwon, Tae gyun. "Structural Analyses of Wind Turbine Tower for 3 kW Horizontal Axis Wind Turbine." DigitalCommons@CalPoly, 2011. https://digitalcommons.calpoly.edu/theses/600.
Full textAbstract:
Structure analyses of a steel tower for Cal Poly's 3 kW small wind turbine is presented. First, some general design aspects of the wind turbine tower are discussed: types, heights, and some other factors that can be considered for the design of wind turbine tower. Then, Cal Poly's wind turbine tower design is presented, highlighting its main design features. Secondly, structure analysis for Cal Poly's wind turbine tower is discussed and presented. The loads that are specific to the wind turbine system and the tower are explained. The loads for the static analysis of the tower were calculated as well. The majority of the structure analysis of the tower was performed using the finite element method (FEM). Using Abaqus, commercial FEM software, both static and dynamic structural analyses were performed. A simplified finite element model that represents the wind turbine tower was created using beam, shell, and inertia elements. An ultimate load condition was applied to check the stress level of the tower in the static analysis. For the dynamic analysis, the frequency extraction was performed in order to obtain the natural frequencies and the mode shapes of the tower. Using the results, the response spectrum analysis and the transient dynamic analysis, which are based on the modal superposition method, were performed in order to see the structure's response for earthquakes that are likely to happen at the wind turbine installation site.
5
Duran, Serhat. "Computer-aided Design Of Horizontal-axis Wind Turbine Blades." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12605790/index.pdf.
Full textAbstract:
Designing horizontal-axis wind turbine (HAWT) blades to achieve satisfactory
levels of performance starts with knowledge of the aerodynamic forces acting on
the blades. In this thesis, HAWT blade design is studied from the aspect of
aerodynamic view and the basic principles of the aerodynamic behaviors of
HAWTs are investigated.
Blade-element momentum theory (BEM) known as also strip theory, which is
the current mainstay of aerodynamic design and analysis of HAWT blades, is used
for HAWT blade design in this thesis.
Firstly, blade design procedure for an optimum rotor according to BEM theory
is performed. Then designed blade shape is modified such that modified blade will
be lightly loaded regarding the highly loaded of the designed blade and power
prediction of modified blade is analyzed. When the designed blade shape is
modified, it is seen that the power extracted from the wind is reduced about 10%
and the length of modified blade is increased about 5% for the same required
power.
BLADESIGN which is a user-interface computer program for HAWT blade
design is written. It gives blade geometry parameters (chord-length and twist
distributions) and design conditions (design tip-speed ratio, design power
coefficient and rotor diameter) for the following inputspower required from a turbine, number of blades, design wind velocity and blade profile type (airfoil type). The program can be used by anyone who may not be intimately concerned with the concepts of blade design procedure and the results taken from the program can be used for further studies.
6
Wang, Tongguang. "Unsteady aerodynamic modelling of horizontal axis wind turbine performance." Thesis, University of Glasgow, 1999. http://theses.gla.ac.uk/4039/.
Full textAbstract:
The present work presents a study of unsteady aerodynamic modelling of horizontal axis wind turbine performance. The unsteady aspects addressed in this work include effects of variations in turbine inflow velocity due to operation in yawed flow, in the atmospheric boundary layer, in a wind tunnel, and due to the tower wake. In each case, the basis for the analysis is a prescribed wake vortex model, the development and enhancement of which has been the main focus of the work. A high resolution model has been developed to meet the requirement for adequate representation of the tower shadow effects. A near wake dynamic model has been enhanced with appropriate modifications and integrated into the prescribed wake scheme to produce a hybrid method capable of predicting the detailed high resolution unsteady response in the tower shadow region. The azimuthal interval used within the shadow region can be reduced to 0.5° whilst the computational cost introduced by the high resolution near wake model is almost negligible. A low order source panel method and the prescribed wake model have been combined into a coupled scheme capable of assessing the basic effect of wind tunnel walls on wind turbine flow and performance. The wind tunnel walls are discretised into a series of panels on which source singularities are placed. The source strengths are related to the turbine bound and wake vorticities via their induced velocities. The geometry of the turbine wake is obtained by superposition of the contribution of the disturbance velocities due to the source panels upon the prescribed wake. This new wake structure modifies the wind turbine aerodynamic performance in turn.
7
Abdulqadir, Sherwan Ahmed. "Turbulence modelling for horizontal axis wind turbine rotor blades." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/turbulence-modeling-for-horizontal-axis-wind-turbine-rotor-blades(2536b213-3a0c-4977-ac39-916a9fce98d2).html.
Full textAbstract:
This Thesis aims to assess the reliability of turbulence models in predicting the flow fields around the horizontal axis wind turbine (HAWT) rotor blades and also to improve our understanding of the aerodynamics of the flow field around the blades. The simulations are validated against data from the NREL/NASA Phase VI wind turbine experiments. The simulations encompass the use of fourteen turbulence models including low-and high-Reynolds-number, linear and non-linear eddy-viscosity models and Reynolds stress models. The numerical procedure is based on the finite-volume discretization of the 3D unsteady Reynolds-Averaged Navier-Stokes equations in an inertial reference frame with the sliding mesh technique to follow the motion of the rotor blades. Comparisons of power coefficient, normalised thrust, local surface pressure coefficients (CP) and the radial variation of the section average of normal force coefficients with published experimental data over a range of tip-speed ratios, lead to the identification of the turbulence models that can reliably reproduce the values of the key performance indicators. The main contributions of this study are in establishing which RANS models can produce quantitatively reliable simulations of wind turbine flows and in presenting the flow evolution over a range of operating conditions. At low (relative to the blade tip speed) wind speeds the flow over the blade surfaces remains attached and all RANS models return the correct values of key performance coefficients. At higher wind speeds there is circumferential flow separation over the downwind surface of the blade, which eventually spreads over the entire surface, Moreover, within the separation bubble the centrifugal force pumps the flow outwards, which at the higher wind speeds suppresses the formation of the classical tip vortices. More refined RANS models which do not rely on the linear effective viscosity approximation generally lead to more reliable predictions over this range of higher wind speeds. In particular the Gibson-Launder version of the Reynolds stress transport model and the high-Re versions of the Lien et al non-linear k-ε produce consistently reliable simulations over the entire range of wind speeds. By contrast some popular linear effective viscosity models, like the SST (k-ω) and the v^2-f, perform the poorest over this complex flow range. Finally all RANS models are also able to predict the dominant (lowest) frequency of the pressure fluctuations and the non-linear effective viscosity models, the Launder and Shima version of RSM and the SST are also able to return some of the higher frequencies measured.
8
Caboni, Marco. "Probabilistic design optimization of horizontal axis wind turbine rotors." Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/7338/.
Full textAbstract:
Considerable interest in renewable energy has increased in recent years due to the concerns raised over the environmental impact of conventional energy sources and their price volatility. In particular, wind power has enjoyed a dramatic global growth in installed capacity over the past few decades. Nowadays, the advancement of wind turbine industry represents a challenge for several engineering areas, including materials science, computer science, aerodynamics, analytical design and analysis methods, testing and monitoring, and power electronics. In particular, the technological improvement of wind turbines is currently tied to the use of advanced design methodologies, allowing the designers to develop new and more efficient design concepts. Integrating mathematical optimization techniques into the multidisciplinary design of wind turbines constitutes a promising way to enhance the profitability of these devices. In the literature, wind turbine design optimization is typically performed deterministically. Deterministic optimizations do not consider any degree of randomness affecting the inputs of the system under consideration, and result, therefore, in an unique set of outputs. However, given the stochastic nature of the wind and the uncertainties associated, for instance, with wind turbine operating conditions or geometric tolerances, deterministically optimized designs may be inefficient. Therefore, one of the ways to further improve the design of modern wind turbines is to take into account the aforementioned sources of uncertainty in the optimization process, achieving robust configurations with minimal performance sensitivity to factors causing variability. The research work presented in this thesis deals with the development of a novel integrated multidisciplinary design framework for the robust aeroservoelastic design optimization of multi-megawatt horizontal axis wind turbine (HAWT) rotors, accounting for the stochastic variability related to the input variables. The design system is based on a multidisciplinary analysis module integrating several simulations tools needed to characterize the aeroservoelastic behavior of wind turbines, and determine their economical performance by means of the levelized cost of energy (LCOE). The reported design framework is portable and modular in that any of its analysis modules can be replaced with counterparts of user-selected fidelity. The presented technology is applied to the design of a 5-MW HAWT rotor to be used at sites of wind power density class from 3 to 7, where the mean wind speed at 50 m above the ground ranges from 6.4 to 11.9 m/s. Assuming the mean wind speed to vary stochastically in such range, the rotor design is optimized by minimizing the mean and standard deviation of the LCOE. Airfoil shapes, spanwise distributions of blade chord and twist, internal structural layup and rotor speed are optimized concurrently, subject to an extensive set of structural and aeroelastic constraints. The effectiveness of the multidisciplinary and robust design framework is demonstrated by showing that the probabilistically designed turbine achieves more favorable probabilistic performance than those of the initial baseline turbine and a turbine designed deterministically.
9
Gomez-Iradi, Sugoi. "CFD for Horizontal Axis Wind Turbines." Thesis, University of Liverpool, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.511051.
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10
Worasinchai, Supakit. "Small wind turbine starting behaviour." Thesis, Durham University, 2012. http://etheses.dur.ac.uk/4436/.
Full textAbstract:
Small wind turbines that operate in low-wind environments are prone to suffer performance degradation as they often fail to accelerate to a steady, power-producing condition. The behaviour during this process is called “starting behaviour” and it is the subject of this present work. This thesis evaluates potential benefits that can be obtained from the improvement of starting behaviour, investigates, in particular, small wind turbine starting behaviour (both horizontal- and vertical-axis), and presents aerofoil performance characteristics (both steady and unsteady) needed for the analysis. All of the investigations were conducted using a new set of aerodynamic performance data of six aerofoils (NACA0012, SG6043, SD7062, DU06-W-200, S1223, and S1223B). All of the data were obtained at flow conditions that small wind turbine blades have to operate with during the startup - low Reynolds number (from 65000 to 150000), high angle of attack (through 360◦), and high reduced frequency (from 0.05 to 0.20). In order to obtain accurate aerodynamic data at high incidences, a series of CFD simulations were undertaken to illustrate effects of wall proximity and to determine test section sizes that offer minimum proximity effects. A study was carried out on the entire horizontal-axis wind turbine generation system to understand its starting characteristics and to estimate potential benefits of improved starting. Comparisons of three different blade configurations reveal that the use of mixed-aerofoil blades leads to a significant increase in starting capability. The improved starting capability effectively reduces the time that the turbine takes to reach its power-extraction period and, hence, an increase in overall energy yield. The increase can be as high as 40%. Investigations into H-Darriues turbine self-starting capability were made through the analogy between the aerofoil in Darrieus motion and flapping-wing flow mechanisms. The investigations reveal that the unsteadiness associated with the rotor is key to predicting its starting behaviour and the accurate prediction can be made when this transient aerofoil behaviour is correctly modelled. The investigations based upon the analogy also indicate that the unsteadiness can be exploited to promote the turbine ability to self-start. Aerodynamically, this exploitation is related to the rotor geometry itself.
11
Campo, Gatell Vanessa del. "Experimenal study of the aerodynamics of a horizontal axis wind turbine." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/116325.
Full textAbstract:
One of the challenges of the wind energy community today is to improve the existing background on the aerodynamic phenomena of a Horizontal Axis Wind Turbine (HAWT), the prediction of the wind speed distribution on the rotor plane, and the estimation of the design loads. This dissertation aims at contributing to the fulfillment of these objectives.
In this way, this study assessed the feasibility of measuring the loads exerted on a HAWT blade by means of Stereoscopic Particle Image Velocimetry (SPIV), which is a non intrusive technique that provides with the whole 3D velocity field in a plane. Thus, with this PIV-Loads method, the velocity and pressure fields, as well as the resultant aerodynamic forces around a section of the blade, would be available simultaneously, without the need of modifying the model or disturbing the flow.
In order to achieve this goal progressively, the PIV-Loads method, based in a Momentum Equation contour-based approach, was firstly validated using DNS data, both for a laminar unsteady flow case, as for a velocity averaged turbulent flow. Secondly, the method was tested in the wind tunnel with a bidimensional problem, measuring forces in a stationary flat plate, for different angles of attack (with laminar and turbulent flow conditions). The force estimation results were compared with those provided by a high sensitive balance. Finally, the PIV-Loads method was applied to a HAWT model working both in axial and yaw flow conditions, measuring forces on a rotating blade for steady and unsteady cases. Final load calculations were compared with those resulting from a numerical simulation based in the Panel method approach. Bringing the project to completion, the near vortex wake of a HAWT was characterized by means of Time Resolved PIV.
Regarding the PIV-Loads methodology, load predictions are more reliable if the integration path does not cross a shear layer or a boundary layer. In addition, it is neither recommended to neglect the third velocity component when measuring forces on a rotating HAWT blade, nor to eliminate the velocity fluctuation terms when dealing with turbulent flows.
All implemented codes and experimental results were validated or compared with numerical or experimental alternative data showing good consistency. The conclusion is that the PIV-Loads method provides with precise results if the available velocity data is sufficiently accurate. However, any PIV errors such as lack of resolution, velocity gradients inside the interrogation window or laser reflections, may lead to uncertainties in the load measurements. Any future improvement in this sense will certainly lead to better results.
12
Tang, Xinzi. "Aerodynamic design and analysis of small horizontal axis wind turbine blades." Thesis, University of Central Lancashire, 2012. http://clok.uclan.ac.uk/7127/.
Full textAbstract:
The exploitation of small horizontal axis wind turbines provides a clean, prospective and viable option for energy supply. Although great progress has been achieved in the wind energy sector, there is still potential space to reduce the cost and improve the performance of small wind turbines. An enhanced understanding of how small wind turbines interact with the wind turns out to be essential. This work investigates the aerodynamic design and analysis of small horizontal axis wind turbine blades via the blade element momentum (BEM) based approach and the computational fluid dynamics (CFD) based approach. From this research, it is possible to draw a series of detailed guidelines on small wind turbine blade design and analysis. The research also provides a platform for further comprehensive study using these two approaches. The wake induction corrections and stall corrections of the BEM method were examined through a case study of the NREL/NASA Phase VI wind turbine. A hybrid stall correction model was proposed to analyse wind turbine power performance. The proposed model shows improvement in power prediction for the validation case, compared with the existing stall correction models. The effects of the key rotor parameters of a small wind turbine as well as the blade chord and twist angle distributions on power performance were investigated through two typical wind turbines, i.e. a fixed-pitch variable-speed (FPVS) wind turbine and a fixed-pitch fixed-speed (FPFS) wind turbine. An engineering blade design and analysis code was developed in MATLAB to accommodate aerodynamic design and analysis of the blades. The linearisation for radial profiles of blade chord and twist angle for the FPFS wind turbine blade design was discussed. Results show that, the proposed linearisation approach leads to reduced manufacturing cost and higher annual energy production (AEP), with minimal effects on the low wind speed performance. Comparative studies of mesh and turbulence models in 2D and 3D CFD modelling were conducted. The CFD predicted lift and drag coefficients of the airfoil S809 were compared with wind tunnel test data and the 3D CFD modelling method of the NREL/NASA Phase VI wind turbine were validated against measurements. Airfoil aerodynamic characterisation and wind turbine power performance as well as 3D flow details were studied. The detailed flow characteristics from the CFD modelling are quantitatively comparable to the measurements, such as blade surface pressure distribution and integrated forces and moments. It is confirmed that the CFD approach is able to provide a more detailed qualitative and quantitative analysis for wind turbine airfoils and rotors. With more advanced turbulence model and more powerful computing capability, it is prospective to improve the BEM method considering 3D flow effects.
13
Wimshurst, Aidan. "Tip flow corrections for horizontal axis wind and tidal turbine rotors." Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:a91acd6f-dc86-4cad-bf5e-b042e81840dc.
Full textAbstract:
On the outboard sections of horizontal axis rotor blades (that are not enclosed within a duct or shroud), vorticity is shed into the wake of the rotor. The shed vorticity induces a downwash at the rotor plane and span- wise flow accelerations along the blade, which causes the blade loading to drop off as the tip is approached. These tip flow effects are currently not adequately accounted for by reduced order rotor models (such as the blade element momentum and actuator line methods) which are frequently used to represent wind and tidal turbine rotors in large simulations. Hence, the rotor thrust and torque may be considerably over-predicted by these models if they are not corrected appropriately for tip flow effects. In this thesis, the tip loss mechanism experienced by both wind and tidal turbine rotor blades is examined directly in a series of simulations, using computational fluid dynamics. Two different correction methods that can account for tip flow effects are then presented and critically evaluated. Both methods are shown to lead to a significant improvement in the accuracy of the computed blade loading, which is principally achieved by allowing the sectional force vector to reduce in magnitude and rotate towards the streamwise direction as the tip of the blade is approached. Tip flow effects also reduce the strength of the suction peak developed on the suction surface of the blade. This reduction has considerable implications for the operation of tidal turbine rotors, since tidal turbine operation may be limited by cavitation inception and cavitation inception is most likely to initiate on the outboard sections of the rotor blade (where the static pressure reaches a minimum). In this thesis, a cavitation analysis of two different tidal turbine rotors is carried out. When tip flow effects are properly accounted for, cavitation inception is shown to be less likely at a given operating condition (tip-speed-ratio and submersion depth). Hence, industry standard cavitation analyses that are based on the blade element momentum method (and do not adequately account for tip flow effects) are shown to be currently overly-conservative. In a separate study, tidal power extraction is examined in a computational domain where the sea bed slopes in the streamwise direction. When the sea bed slopes downwards in the streamwise direction, the velocity shear across the swept area of the rotor increases, increasing the power available for extraction. However, the increased velocity shear also increases the strength of the suction peak developed on the blade at top dead centre, so the device is more likely to cavitate at a given tip-speed-ratio. Conversely, when the sea bed slopes upwards in the streamwise direction, the incident velocity profile is more uniform, so the device is less likely to cavitate at a given tip-speed-ratio. Power extraction is also found to be more efficient on the upwards facing slope, as the flow through the swept area of the rotor is accelerated by the downstream flow passage constriction. At higher blockage ratios, the strength of the suction peak is further increased by the acceleration of the flow through the swept area of the rotor, so the device is even more likely to cavitate at a given tip-speed-ratio.
14
Khamlaj, Tariq A. "Analysis and Optimization of Shrouded Horizontal Axis Wind Turbines." University of Dayton / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1543845571758119.
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15
Xu, Guanpeng. "Computational studies of horizontal axis wind turbines." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/12081.
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16
Feitosa, Evaraldo Alencar Do Nacimento. "Parametric resonance in horizontal axis wind turbines." Thesis, University of Southampton, 1989. https://eprints.soton.ac.uk/52253/.
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Regions of parametric resonance are predicted for the flexible blades of Horizontal Axis Wind Turbines subjected to periodic parametric loading due to gravity. The mathematical model consists of rigid blade flapping, rigid blade lagging and shaft torsion degrees of freedom. A hypothetical hinge offset, flapping and lagging stiffnesses, and aerodynamic loading are considered in the model. Also, hinge inclination which induces stiffness coupling is included in the analysis. The equations of motion (Mathieu/Hill's equations) are investigated using the Harmonic Balance Method for the determination of the main parametric resonance. The analysis has been carried out with the support of the computer algebra system REDUCE. Particular attention is given to: the importance of aerodynamic terms; the influence of coning angle; the influence of the flapping and lagging stiffnesses and the influence of the hinge inclination. The size and position of these regions of instability are significantly affected by these factors. Experimental results are presented from wind tunnel tests in which a Horizontal Axis Wind Turbine model of 1.82m diameter with flexible blades was investigated. The experimental results show clearly some regions of parametric resonance
17
Yucel, Burak. "Performance Prediction Of Horizontal Axis Wind Turbines Using Vortex Theory." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605715/index.pdf.
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iv
Performance prediction of HAWTs is important because it gives an idea
about the power production of a HAWT in out of design conditions without making
any experiments. Since the experiments of fluid mechanics are difficult to afford,
developing some models is very beneficial.
There are some models developed about this subject using miscellaneous
methods. In this study, one can find &ldquoVortex Theory&rdquo
among one of these theories. Some basic 3D aerodynamics was discussed in order to make the reader to understand the main subject of this study. Just after that, performance prediction of constant speed, stall controlled HAWTs was discussed. In order to understand the closeness of this theory to experiments, as a sample, NREL &ldquo
Combined Experiment Rotor&rdquo
was considered. Performances obtained by AEROPOWER, written in Visual Basic 6.0 and Excel combination, and experimental results were compared for different wind velocities. Acceptable results were obtained for wind speeds not much different than the design wind speed. For relatively lower wind speeds, due to &ldquo
turbulence&rdquo
, and for relatively higher wind speeds, due to &ldquo
stall&rdquo
, the program did not give good results. In the first case it has not given any numerical result. Power curves were obtained by only changing the settling angle, and only changing the rotor angular speed using AEROPOWER. It was seen that, both settling angle and rotor rpm values influence the turbine power output significantly.
18
Pratumnopharat, Panu. "Novel methods for fatigue data editing for horizontal axis wind turbine blades." Thesis, Northumbria University, 2012. http://nrl.northumbria.ac.uk/10458/.
Full textAbstract:
Wind turbine blades are the most critical components of wind turbines. Full-scale blade fatigue testing is required to verify that the blades possess the strength and service life specified in the design. Unfortunately, the test must be run for a long time period. This problem led the blade testing laboratories to accelerate fatigue testing time. To achieve the objective, this thesis proposes two novel methods called STFT- and WT-based fatigue damage part extracting methods which are based on short-time Fourier transform (STFT) and wavelet transform (WT), respectively. For WT, different wavelet functions which are Morl, Meyr, Dmey, Mexh and DB30 are studied. An aerodynamic computer code, HAWTsimulator, based on blade element momentum theory has been developed. This code is used to generate the sets of aerodynamic loads acting along the span of a ‘SERI-8 wind turbine blade’ in the range of wind speed from cut-in to cut-out. SERI-8 blades are installed on 65 kW wind turbines. Each set of aerodynamic loads is applied on the finite element model of the SERI-8 blade in structural software (ANSYS) to generate a plot of von Mises stress at the critical point on the blade versus wind speed. By relating this relationship to the wind speed data, the stress-time history at the critical point on the SERI-8 blade can be generated. It has the same sampling rate and length as the wind speed data. A concept of applying accumulative power spectral density (AccPSD) distribution with time to identify fatigue damage events contained in the stress-time history has been introduced in this thesis. For STFT, AccPSD is the sum of power spectral density (PSD) of each frequency band at each time interval in the spectrogram. For WT, AccPSD is the sum of PSD of wavelet coefficients of each scale at each time interval in the scalogram. It has been found that the locations of AccPSD spikes imply where the fatigue damage events are. Based on an appropriate AccPSD level called a cutoff level, the fatigue damage events can be identified at time location of the stress-time history. A fatigue computer code, HAWTfatigue, based on stress-life approach and Miner’s linear cumulative damage rule has been developed. Basically, the code is used for evaluating the fatigue damage and service lifetime of horizontal axis wind turbine blade. In addition, the author has implemented STFT- and WT-based fatigue damage part extracting methods into the code. Fatigue damage parts are extracted from the stress time history and they are concatenated to form the edited stress-time history. The effectiveness of STFT- and WTbased algorithms is performed by comparing the reduction in length and the difference in fatigue damage per repetition of the edited stress-time histories generated by STFT and WT to those of the edited stress-time history generated by an existing method, Time Correlated Fatigue Damage (TCFD) used by commercial software. The findings of this research project are as follows: 1. The comparison of the reduction in length of the edited stress-time histories generated by TCFD, STFT and WT indicates that WT with the Mexh wavelet has the maximum reduction of 20.77% in length with respect to the original length, followed by Meyr (20.24%), Dmey (19.70%), Morl (19.66%), DB30 (19.19%), STFT (15.38%), and TCFD (10.18%), respectively. 2. The comparison of the retained fatigue damage per repetition in the edited stress-time histories generated by TCFD, STFT and WT indicates that TCFD has the retained fatigue damage per repetition less than the original fatigue damage per repetition by 0.076%, followed by Mexh (0.068%), DB30 (0.063%), STFT (0.045%), Meyr (0.032%), Dmey (0.014%), and Morl (0.013%), respectively. 3. Both comparison of reduction in length and comparison in the retained fatigue damage per repetition of the edited stress-time histories suggest that WT is the best method for extracting fatigue damage parts from the given stress-time history. It has also been indicated that not only do STFT and WT improve accuracy of fatigue damage per repetition retained in the edited stress-time histories, but also they provide the length of the edited stress-time histories shorter than TCFD does. Thus, STFT and WT are useful methods for performing accelerated fatigue tests. 4. It has been found that STFT is controlled by two main factors which are window size and cutoff level. Also, WT is controlled by three main factors which are wavelet decomposition level, cutoff level and wavelet type. To conclude, the edited stress-time history can be used by blade testing laboratories to accelerate fatigue testing time. STFT- and WT-based fatigue damage part extracting methods proposed in this thesis are suggested as alternative methods in accelerating fatigue testing time, especially for the field of wind turbine engineering.
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Vimalakanthan, Kisorthman. "Passive flow control devices for a multi megawatt horizontal axis wind turbine." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/12132.
Full textAbstract:
Renewable energy is an environmentally friendly alternative to the use of fossil fuels. In
response to reducing the dependency on fossil fuels, the European Wind Energy Association
(EWEA) has made a policy to increase the overall renewable energy consumption by three
times the current amount by the year 2020. Critical to achieving this target will be the use of
wind turbines. There is a scope to increase the performance of wind turbines by utilising the
existing techniques from the aeronautical industry. One of these techniques is the use of
passive flow control which involves no moving parts that has a reduced complexity
compared to active flow control techniques.
Initially eleven flow control devices applicable for a wind turbine were identified. Out of the
eleven devices four possible flow control devices were selected for this research project
(vortex generator, vortex trapping, passive ventilation and sinusoidal leading edge wing).
These four concepts have been evaluated for their applicability for a wind turbine. A novel
CFD work was conducted for a wedge type vortex generator for wind turbine blade. A
number of different configurations as well as its performance over different operating
conditions were assessed. The wedge type vortex generator (VG) showed the most benefit
for a wind turbine blade and it is recommended for wind turbine application, specifically for
the root part of the blade. It was found that up to 0.2% increase in AEP is possible with
integration of this VG at the blade root, which corresponds to about €30,000 worth of
additional energy production of a 5MWturbine per annum.
A series of theoretical studies using Blade Element Momentum (BEM) theory was conducted
to establish the requirements for an optimum wind turbine blade. Based on this
investigation it was found that the current root geometry is unable to attain the optimum
lift force and in fact it produces negative torque.
One of the interests of this project was to identify ways to reduce the blade loads. This
simple BEM based investigation was conducted to quantify potential the chord reduction
available with the use of conventional vane and passive air-jet vortex generators (PAJVG).
Findings from this exercise showed that large chord reductions are possible with the use of
these devices. Only the PAJVGs were able to attain chord reduction up to 10% while
allowing the blade to operate within a safe stall margin.
Extensive number of 2D CFD simulations was conducted to validate the current 2D CFD
methods. Baseline 2D CFD methods have been successfully validated for the pre-stall angle
of attack. The effect of modelling transition for a 2D and 3D wind turbine simulation has
been established using the Menter’s SST γ-θ transition model.
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Poole, Sean. "The development of a segmented variable pitch small horizontal axis wind turbine with active pitch control." Thesis, Nelson Mandela Metropolitan University, 2013. http://hdl.handle.net/10948/d1020583.
Full textAbstract:
Small scale wind turbines operating in an urban environment produce dismal amounts of power when compared to their expected output [1-4]. This is largely due to the gusty wind conditions found in an urban environment, coupled with the fact that the wind turbines are not designed for these conditions. A new concept of a Segmented Variable Pitch (SVP) wind turbine has been proposed, which has a strong possibility to perform well in gusty and variable wind conditions. This dissertation explains the concept of a SVP wind turbine in more detail and shows analytical and experimental results relating to this concept. Also, the potential benefits of the proposed concept are mentioned. The results from this dissertation show that this concept has potential with promising results on possible turbine blade aerofoil configurations. Scaled model tests were completed and although further design optimisation is required, the tests showed good potential for the SVP concept. Lastly a proof-of-concept full scale model was manufactured and tested to prove scalability to full size from concept models. Along with the proof-of-concept full scale model, a wireless control system (to control the blade segments) was developed and tested.
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Taylor, D. "The design and testing of a horizontal axis wind turbine with sailfoil blades." Thesis, Open University, 1985. http://oro.open.ac.uk/54193/.
Full textAbstract:
The work contained in this thesis covers the design, development and testing of a horizontal axis wind turbine (HAWT) with Sailfoil blades. Included is a brief history of wind turbine technology, its revival, a review of current wind energy developments and a literature survey of previous work on wind turbines with sail type blades. The Sailfoil blade consists of a framework of a leading edge D spar and a rigid trailing edge spar over which is stretched a fabric sock, forming a wing-like surface. The aerodynamic performance theories of HAWTs are described, as is the aerodynamic, structural and mechanical design of a 4 metre diameter, 3 bladed HAWT with Sailfoil blades. A wind turbine test facility was designed and developed for free air testing of wind turbines and is described. Free air tests were carried out on the Sailfoil wind turbine on the test facility to obtain power coefficient versus tip speed ratio curves and power versus wind speed curves for the wind turbine. These are presented and compared to predicted values.
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Shawler, James R. "Engineering aerodynamics of horizontal axis wind turbines (HAWTs)." Thesis, Loughborough University, 2004. https://dspace.lboro.ac.uk/2134/7629.
Full textAbstract:
This thesis comprises two main original contributions. The first concerns the aeroelastic modelling of a large-scale prototype wind turbine undertaken specifically to explain experimentally observed mechanical instabilities. The second explores the aerodynamic aspect of turbine modelling in greater detail since this is the main identified technical challenge, this process makes use of detailed largescale wind tunnel test data from NREL for model validation purposes. The MS4 prototype wind turbine was modelled using ADAMS/WT software, the aerodynamic model was provided by the NREL AERODYN subroutines. The drivetrain instability of the machine of 0.75Hz was reproduced by the computer simulation. The causes of the instability were found to be negative aerodynamic damping, complex blade bending modes caused by the blade design and rapid yawing and tilting inducing Coriolis forces in the rotor structure. Accurate analysis of the aerodynamic forces acting on the MS4 was not possible because of the lack of detailed data available and the complicated aeroelastic response of its flexible structure. Theoretical comparisons with the results from the NREL wind tunnel tests were made using several different engineering aerodynamic models (including those used with AERODYN). It was found that blade element aerofoil data had a controlling influence on the blade forces predicted through theory. The effect of inflow models was found to be marginal at lower tip speed ratios and to decrease with decreasing tip speed ratio. Experimental blade forces at low tip speed ratios were found to be defined by gross 3 dimensional effects and the use of 2 dimensional aerofoil data led to inaccurate prediction of blade forces. The use of a stall delay model improved results but was not convincing. Yawed flow predictions were again controlled by the blade element aerofoil data used, use of a stall delay model again improved results in a steady state fashion. A dynamic stall model also improved results but the phasing of results towards the blade root was questionable and may be caused by unsuitable time constants or the influence of the delayed stall effect.
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Simoes, Francisco Jose. "A steady inviscid flow model for horizontal axis wind turbine rotors under high loading." Thesis, Imperial College London, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261843.
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Poole, Sean Nichola. "Optimisation of a mini horizontal axis wind turbine to increase energy yield during short duration wind variations." Thesis, Nelson Mandela Metropolitan University, 2017. http://hdl.handle.net/10948/7036.
Full textAbstract:
The typical methodology for analytically designing a wind turbine blade is by means of blade element momentum (BEM) theory, whereby the aerofoil angle of attack is optimized to achieve a maximum lift-to-drag ratio. This research aims to show that an alternative optimisation methodology could yield better results, especially in gusty and turbulent wind conditions. This alternative method looks at increasing the aerofoil Reynolds number by increasing the aerofoil chord length. The increased Reynolds number generally increases the e_ectiveness of the aerofoil which would result in a higher or similar lift-to-drag ratio (even at the decreased angle of attacked require to maintain the turbine thrust coe_cient). The bene_t of this design is a atter power curve which causes the turbine to be less sensitive to uctuating winds. Also, the turbine has more torque at startup, allowing for operatation in lower wind speeds. This research is assumed to only be applicable to small wind turbines which operated in a low Reynolds number regime (<500 000), where Reynolds number manipulation is most advantageous.
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Al-Hadad, Mohammed. "Vibration Fault Detection for Horizontal Axis Wind Turbines (HAWT)." Thesis, Curtin University, 2019. http://hdl.handle.net/20.500.11937/77966.
Full textAbstract:
This research has investigated novel vibration condition monitoring methods for horizontal-axis wind turbines for a range of case studies simulating various failure modes of the blades and tower, including the effect of coupling of rotating and non-rotating components of the system. A small scale experimental test rig has been created and developed to monitor vibration behaviour under different transient loads as a function of rotor phase, including the measurement of blade, driveshaft, and tower vibrations.
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Perry, Dylan R. "AERODYNAMIC DESIGN AND STRUCTURAL ANALYSIS PROCEDURE FOR SMALL HORIZONTAL-AXIS WIND TURBINE ROTOR BLADE." DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1375.
Full textAbstract:
This project accomplished two correlated goals of designing a new rotor blade to be used with the Cal Poly Wind Power Research Center, as well as defining the methodology required for the aerodynamic analysis of an optimized blade, the procedure required for generation of an accurate CAD model for the new blade geometry, and structural integrity verification procedure for the new blade via finite element analysis under several operating scenarios. The new rotor blades were designed to perform at peak efficiency at a much lower wind speed than the current CPWPRC rotor blades and incorporated a FEA verification process which was not performed on the earlier rotor blade design.
Since the wind characteristics relative to the location of the CPWPRC are essentially unchanging the most viable option, in regards to generating power for longer periods of time, is to redesign the HAWT rotor to capture more of the wind energy available. To achieve this, the swept area of the rotor was increased, suitable airfoils were utilized, and the new rotor blades were optimized to maximize their performance under the CPWPRC location’s wind conditions.
With an increased magnitude of wind energy being captured the aerodynamic loading on the rotor blades simultaneously increased which necessitated a structural analysis step to be implemented, both with classical hand calculations and with the assistance of an adequate FEA program, to ensure the new rotor blades did not fail under normal or extreme wind conditions. With the completion of this project the new rotor blade designed and analyzed in this report may be finalized and refined in order to be incorporated into the CPWPRC system in the future or the methodology defined throughout this project may be used to design an entirely different aerodynamically optimized rotor blade, including a CAD model and FEA structural integrity verification, as well.
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Farhan, Ali M. "Numerical study of the effect of winglets on a horizontal axis wind turbine performance." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/22493/.
Full textAbstract:
With increasing demand for producing clean and pollution free energy, special attention has been paid to wind turbines and improving their performance. Reducing the effect of wingtip vortices on the wind turbine performance can be achieved by using winglets which work to weaken the impact of wingtip vortices by diffusing them away from the blade tips. The general trend of the literature has considered winglets as diffusers of the wingtip vortices. However, extending the span of the turbine rotor by attaching winglet could improve the potential of a rotor to capture more kinetic energy from moving air. Accordingly, the winglet planform and airfoil play vital roles in wind turbines performance. The present work reports on the study of the effect of winglet planform and winglet airfoil on the wind turbine performance using Computational Fluid Dynamics (CFD) tools. The National Renewable Energy Laboratory (NREL) phase VI rotor is used as a baseline rotor and the CFD results are validated with the experimental data in terms of torque, pressure and normal force coefficients for different wind speeds. In this study, two turbulence models are used, which are the SST k-ω and the Spalart-Allmaras models, which can be used to predict the properties of the fluid flow in the computational domain. Both of the models show a good match of the numerical results when compared to the experimental data, at a range of low wind speeds from 5m/s to 8m/s, due to the absence of stalled flow. At higher wind speeds of 10m/s, the SST k-ω model shows a better match between the calculated torque and the experimental measurements. Consequentially, the SST k-ω model is implemented to predict the behaviour of fluid flow in all the CFD calculations in the present study. The aerodynamic behaviour of two winglet planforms is investigated. These are rectangular and elliptical winglets to increase the NREL phase VI rotor performance. The performances of four winglet configurations are assessed when compared to the baseline power, at the range of wind speeds from 5m/s to 25m/s. The configurations are obtained by changing the winglet planforms and airfoils using the S809 and PSU 94-097 airfoils. In this regard, the elliptical planform causes a minimizing of the wingtip vortices, more than the rectangular planform, due to the reduction of the elliptical tip by 75% when compared to the rectangular tip. A rectangular planform shows a better performance than the elliptical planform in percentages of power increase. The highest percentage in the power increase is achieved by attaching the rectangular planform that tilted by a cant angle of 45o and extended by 15cm. This improvement is slightly more than 9%, at the range of low wind speeds from 5m/s to 10m/s, since the flow is almost attached. Considering the effect of winglet airfoil, the study reports that, choosing a suitable winglet airfoil is mainly dependent on the aerodynamic coefficients of the selected airfoil, such as lift coefficient (Cl), drag coefficient (Cd) and moment coefficient (Cm). For this purpose, a preliminary analysis is conducted using the Xfoil code to predict the aerodynamic coefficients of selected airfoils (S801, S803, S805A and S806A airfoils). The S806A and S805A airfoils are chosen to create two different configurations. The 3D calculations show more increase in the NREL phase VI power is achieved by attaching the configuration that created using the S806A airfoil since this airfoil has less drag coefficient.
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Sagol, Ece. "Site Specific Design Optimization Of A Horizontal Axis Wind Turbine Based On Minimum Cost Of Energy." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12611604/index.pdf.
Full textAbstract:
This thesis introduces a design optimization methodology that is based on minimizing the Cost of Energy (COE) of a Horizontal Axis Wind Turbine (HAWT) that is to be operated at a specific wind site. In the design methodology for the calculation of the Cost of Energy, the Annual Energy Production (AEP) model to calculate the total energy generated by a unit wind turbine throughout a year and
the total cost of that turbine are used. The AEP is calculated using the Blade Element Momentum (BEM) theory for wind turbine power and the Weibull
distribution for the wind speed characteristics of selected wind sites. For the blade profile sections, either the S809 airfoil profile for all spanwise locations is used or NREL S-series airfoil families, which have different airfoil profiles for different spanwise sections, are used,. Lift and drag coefficients of these airfoils are obtained by performing computational fluid dynamics analyses. In sample
design optimization studies, three different wind sites that have different wind speed characteristics are selected. Three scenarios are generated to present the effect of the airfoil shape as well as the turbine power. For each scenario, design optimizations of the reference wind turbines for the selected wind sites are performed the Cost of Energy and Annual Energy Production values are
compared.
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Pesmajoglou, Stelianos. "Three-dimensional wake computations applied to horizontal axis wind turbines." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367829.
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Kazacoks, Romans. "A generic evaluation of loads in horizontal axis wind turbines." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=28479.
Full textAbstract:
Thousands of load calculations for wind turbine design have been calculated by manufactures, consultants and certification bodies. These have been done as required to develop and validate specific designs. However, there has not been a general systematic study of trends in loads related to key wind turbine design parameters and external operating conditions. The aim of this thesis is parameterise and quantify trends of extreme and fatigue loads based on systematic modifications of wind turbine characteristics. This thesis is in two main parts. The first part provides an overview of loads calculation methods, flow modelling and approach adopted also considering scaling rules, comparing scaling with similarity and the scaling evident in from commercial world turbines data. The second part presents and evaluates loading trends for extreme and fatigue loads related to systematic alterations of key wind turbine parameters. Three chapters of results investigate the load impacts of blade structural properties, rotor solidity and up-scaling respectively. The chapter on blade structural properties demonstrates that the self-weight of blades is a major component influencing loads of the blade root and hub. The chapter on rotor solidity shows that significant load reduction can result for blade root, shaft and yaw bearing in reducing the solidity of rotor. However, the aerodynamic damping reduces with reducing solidity, which is crucial for tower base fore-aft loads; therefore the reducing rotor solidity has an adverse impact on the tower base fore-aft loads. The chapter on up-scale demonstrates that up-scaling with similarity method can give good prediction of loads with an error of ±10% and ±15% for extreme and fatigue loads of large wind turbines (up to 10MW) at the mean wind speed within power production range. Additional, the chapter of up-scaling showed that the up-scaled wind turbines reduce the sensitivity to turbulence with the size of rotor.
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Elfarra, Monier A. K. "Horizontal Axis Wind Turbine Rotor Blade: Winglet And Twist Aerodynamic Design And Optimization Using Cfd." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12612987/index.pdf.
Full textAbstract:
The main purpose of this study is to aerodynamically design and optimize winglet, twist angle distribution and pitch angle for a wind turbine blade using CFD to produce more power. The RANS solver of Numeca Fine/Turbo was validated by two test cases, the NREL II and NREL VI blades. The results have shown a
considerable agreement with measurements for both cases. Two different preconditioners have been implemented for the low Mach number flow. The results have shown the superiority of Merkle preconditioner over Hakimi one and Merkle
was selected for further simulations. In addition to that, different turbulence models have been compared and the Launder &ndashSharma has shown the best agreement with measurements. Launder &ndash
Sharma was chosen for further simulations and for the design process. Before starting the design and optimization, different winglet configurations were studied. The winglets pointing towards the suction side of the blade have yielded higher power output. Genetic algorithm and artificial neural network were implemented in the design and optimization process. The optimized winglet has shown an increase in power of about 9.5 % where the optimized twist has yielded to an increase of 4%. Then the stall regulated blade has been converted into pitch regulated blade to yield more power output. The final design was produced by a combination of the optimized winglet, optimized twist andbest pitch angle for every wind speed. The final design has shown an increase in power output of about 38%.
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Chen, Hao. "Numerical study of trailing edge flow control for horizontal axis wind turbines." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/13354/.
Full textAbstract:
Wind turbines have been developed for more than a century and nowadays wind turbines are still facing some challenges such as efficiency and maintenance problems. Load control is considered to be one of the most important parts for future horizontal axis wind turbine (HAWT) designs. Deploying effective flow control devices on the blades could either increase loads at off-design wind speed conditions or reduce the extreme loads, leading to either higher energy output or a more stable energy output from the wind turbine. This study reports a research into the performance of trailing edge flow control devices of HAWT by solving the Reynolds averaged Navier-Stokes equations. The validation case selected for this work is the NREL Phase VI blade with experimental data. The trailing edge flow control devices studied include microtabs and microjets installed near the trailing edge of the rotating blade. The divergent trailing edge is also included in the study as a passive flow control device due to its practical interest. These trailing edge devices are implemented on the fixed-pitch NREL Phase VI blade, using the original performance and flow characteristics as a benchmark. Both 2D and 3D simulations are carried out in order to investigate the suitability of the 2D blade sectional design analysis and control for the actual 3D rotating framework. Moreover, the study is extended to an active pitch-regulated offshore wind turbine, NREW 5MW wind turbine. Firstly the code to code comparison is carried out for validation purpose. Then the trailing edge flow control devices are also deployed on this wind turbine to find out their effectiveness. The results show there are significant differences when compared to the conclusions from the CFD study on the NREL Phase VI blade.
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Newey, Kerryn Brett. "The development of an optimised rotor software design tool to improve performance of small horizontal axis wind turbines." Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1009431.
Full textAbstract:
Horizontal axis wind turbines are by far the most common and well understood forms of wind turbine. Typically a large amount of research and development has been invested in the technology of large scale wind turbines. Unfortunately, development of small machines (rotor diameter smaller than 10 metres) has not been as forthcoming. The advantages of small turbines are that they are accessible to the individual consumer and they are a very attractive project for the home builder. The disadvantage of small turbines is that due to the negative influence of economies of scale, they tend to be costly in relation to their power output and suffer from a long-term return on investment. Furthermore, trends in the wind industry have shown that smaller machines tend to be relatively simple devices that have been developed with very little research and development. As a result, small turbines can be inefficient, unreliable and expensive to maintain. In many cases rotor design is less than optimal, with very little blade refinement. This is especially critical for small rotors due to low Reynolds Number operation. Further exacerbating the problem is that the rotors are typically not well matched to the generator. In many cases the machines are not suited to the wind speed range in which they are designed to operate, reducing the financial viability due to poor performance. It is envisaged that by applying optimising techniques and automating some of the design complexities into a software design tool, more cost-effective and viable machines can be developed that will deliver improved performance and therefore become more financially viable.
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Pietrangeli, Sven. "Comparison of fixed diameter and variable diameter wind turbines driving a permanent magnet hub motor." Thesis, Cape Peninsula University of Technology, 2012. http://hdl.handle.net/20.500.11838/1283.
Full textAbstract:
Thesis submitted in fulfilment of the requirements for the degree
MAGISTER TECHNOLOGIAE: Mechanical Engineering
in the
FACULTY OF ENGINEERING
at the
CAPE PENINSULA UNIVERSITY OF TECHNOLOGY, 2012The amount of power a horizontal axis wind turbine (HAWT) can produce is determined by two main factors, wind velocity and rotor swept area. Theory dictates that the power production of a horizontal wind turbine is related to the cube of wind velocity and the square of the turbine diameter (or radius). The power produced at any given time is thus dependent on of the wind velocity and the rotor swept area of the turbine. Wind is variable in availability and consistency. Very little can be done to effect the wind velocity passing through the turbine rotor area and its effect is minimal. Thus understandably if more power is required, from the same wind velocity, the rotor diameter must be increased. A variable length blade can adapt lengthwise to accommodate low wind velocities and similarly high wind velocities during extreme conditions, thus increasing the operational time and power production of the turbine. The work undertaken in this thesis is a comparative study between standard design, fixed length blades to that of a modified design, variable length blade. The project entailed the design and development of small diameter HAWT blades and experimental testing. The turbine blades were designed using applicable theory and manufactured from available materials. For the experiments, the turbine was mounted on a vehicle and driven at various speeds. Due to size limitations, no dynamic adaption was done during testing. The variable length design blade was obtained by cutting increments off. The results obtained from each test were compared at corresponding points and conditions. Final interpretation of results lead to the conclusion that by increasing or decreasing the turbine blade length the area of turbine energy capture can be adjusted to affect the amount of power produced. Additional benefits included, force reduction during extreme operating conditions, extended production period for the turbine and a mechanical start up method during low wind speeds. The financial feasibility did not form part of the scope of this thesis and the technical feasibility of the concept can be thoroughly addressed in future research.
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Benjanirat, Sarun. "Computational studies of the horizontal axis wind turbines in high wind speed condition using advanced turbulence models." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-08222006-145334/.
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Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2007.Samual V. Shelton, Committee Member ; P.K. Yeung, Committee Member ; Lakshmi N. Sankar, Committee Chair ; Stephen Ruffin, Committee Member ; Marilyn Smith, Committee Member.
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Gomez, Gonzalez Alejandro [Verfasser]. "Aerodynamic and Aeroelastic Rotor-Tower Interaction in Horizontal Axis Wind Turbines / Alejandro Gomez Gonzalez." München : Verlag Dr. Hut, 2010. http://d-nb.info/1009972812/34.
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Alexeev, Timur. "Computational aeroelasticity study of horizontal axis wind turbines with coupled bending - torsion blade dynamics." Thesis, University of California, Davis, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3614169.
Full textAbstract:
With the increasing size of wind turbines and the use of flexible and light materials in aerodynamic applications, aeroelastic tailoring for power generation and blade stability has become an important subject in the study of wind turbine dynamics. To this day, coupling of bending and torsion in wind turbine rotor blades has been studied primarily as an elastic mechanism due to a coupling laminate construction. In this report, inertial coupling of bending and torsion, due to offset of axis of elasticity and axis of center of mass, is investigated and numerical simulations are performed to test the validity of the constructed model using an in-house developed aeroelastic numerical tool. A computationally efficient aeroelastic numerical tool, based on Goldstein's helicoidal vortex model with a prescribed wake model and modal coupling of bending and torsion in the blades, is developed for 2-bladed horizontal axis wind turbines and a conceptual study is performed in order to argue the validity of the proposed formulation and numerical construction. The aeroelastic numerical tool, without bending-torsion coupling, was validated (Chattot 2007) using NREL Phase VI wind turbine data, which has become the baseline model in the wind turbine community. Due to novelty of the proposed inertial bending-torsion coupling in the aeroelastic model of the rotor and lack of field data, as well as, other numerical tools available for code to code comparison studies, a thorough numerical investigation of the proposed formulation is performed in order to validate the aeroelastic numerical tool Finally, formulations of geometrically nonlinear beams, elastically nonlinear plates and shells, and a piecewise linear, two degree of freedom, quasi steady, aerodynamic model are presented as an extension for nonlinear wind turbine aeroelastic simulations. Preliminary results of nonlinear beams, plates, shells, and 2 DOF NACA0012 aeroelastic model are presented.
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Korobenko, Artem. "Advanced Fluid--Structure Interaction Techniques in Application to Horizontal and Vertical Axis Wind Turbines." Thesis, University of California, San Diego, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3670451.
Full textAbstract:
During the last several decades engineers and scientists put significant effort into developing reliable and efficient wind turbines. As a wind power production demands grow, the wind energy research and development need to be enhanced with high-precision methods and tools. These include time-dependent, full-scale, complex-geometry advanced computational simulations at large-scale. Those, computational analysis of wind turbines, including fluid-structure interaction simulations (FSI) at full scale is important for accurate and reliable modeling, as well as blade failure prediction and design optimization.
In current dissertation the FSI framework is applied to most challenging class of problems, such as large scale horizontal axis wind turbines and vertical axis wind turbines. The governing equations for aerodynamics and structural mechanics together with coupled formulation are explained in details. The simulations are performed for different wind turbine designs, operational conditions and validated against field-test and wind tunnel experimental data.
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Khan, Muhammad Mohsin K. "Reliability analysis and condition monitoring or a horizontal axis wind turbine /." 2005.
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Wu, Pei-Rong, and 吳培榕. "Development Of Wind Direction Tracking System For Horizontal Axis Wind Turbine." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/49226959949173197007.
Full textAbstract:
碩士聖約翰科技大學
電機產業研發碩士專班
100
Due to the increase of the atmospheric carbon dioxide (CO2) concentration, the renewable energy, also called “green energy”, without any emission of CO2 has attracted much attention to replace the traditional combustion of fossil fuel. To date, the horizontal axis wind power generator is one of the most efficient renewable energy sources. However, its efficacy is highly dependent on the wind direction. In this work, a control system allowing the horizontal axis wind power generator to automatically track wind direction changes is developed and adopted PIC16F73 microprocessor designed by Microchip Tec. Inc.as a core component. Through practical tests, this control system is applicable for the horizontal axis wind power generator to take the best advantage of wind by tracking the wind direction.
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"COMPUTER-AIDED DESIGN OF HORIZONTAL-AXIS WIND TURBINE BLADES." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12605790/index.pdf.
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Tsai, Shan-Han, and 蔡深翰. "The Study of Horizontal-Axis Wind Turbine with Diffusers." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/81268659039267109587.
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碩士淡江大學
航空太空工程學系碩士班
101
This study used the computational fluid dynamics software, Fluent, and computer aided design softwares, Pro/Engineer, Gambit, and Tecplot to study the flow field of horizontal-axis wind turbine, HAWT, with diffusers. This study was divided into two parts. The first part studied the effects of various parameters on the acceleration performance of a diffuser. These parameters included diffuser body length, expansion angle, flange, and inlet shroud. The second part investigated the effects of combining the blades and diffuser. We calculated the torque generated by the blades and the corresponding power coefficient. The results of this study show that the addition of diffuser can improve the efficiency of small HAWTs. We also found that the flow field of small HAWTs is laminar flow. When a turbulent flow was assumed in Fluent, the calculated torque became too small, because the friction drag on the blades was too large. The flow in the diffusers which provide better acceleration is turbulent, but the flow in small HAWTs is laminar. How to combine these two flow fields together needs further study.
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Lee, Hu Chia, and 李胡嘉. "Design of 10kW Horizontal Axis Wind Turbine Assembled Blades." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/5aw6b6.
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碩士長庚大學
機械工程學系
105
The size and weight of a wind turbine blade increase with the output power of the wind turbine. The increase of blade mass represents the increase of rotor inertia that increases the cut-in wind speed and reduces the energy efficiency of the wind turbine. To reduce the mass of the blades, composit materials are often used to build hollow blades but the manpower and time are costly. In this study, the blades of a 10 kW horizontal axis wind turbine are analized and optimally designed with material mechanics, aerodynamics, and Taguchi method in order to produce hollow blades assembled by injection molding parts using fiberglass reinforced Nylon, which is suitable for mass production and effectively reduces the weight and cost. The blade has seven parts, three parts and four parts on the windward side and leeward side, respectively. To strengthen the assembly, each part on the windward side has ribs and bumps on the ribs, which are fit to the notches on the leeward side. The geometric parameters of the ribs and the bumps are optimized with Taguchi method for minimizing stress and blade tip displacement under normal operation. To evaluate the stress and blade tip displacement, ANSYS® is used with the boundary conditions of the axial and tangential forces predicted by the blade element momentum theory. The results show that the solid blade weights 36.3 kg and has a maximum stress of 28.3 MPa and a blade tip displacement of 67 mm. The opimized blade assembly weights only 14.7 kg and has a maximum stress of 80.4 MPa and a blade tip displacement of 98 mm. Even though the maximum stress of the later is more than twice that of the former, it is still less than the 122 MPa yielding strength of the material. The blade tip displacement of the optimized blade is acceptable (< 100 mm). Most important of all, the mass of the optimized blade is 60% less than that of the solid blade. If the content of the fiberglass to Nylon is reduced, the mass and the maximum stress of the blade will reduce. However, the blade tip displacement increases greatly that the blade tip may hit the mast and cause damage to the blade and mast. Therefore, the 50% content of fiberglass is recomanded.
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Yi-ChenKuo and 郭奕甄. "The Performance Analysis of Rotor Blades for Horizontal-Axis Wind Turbine (HAWT) and Vertical-Axis Wind Turbine (VAWT)." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/50081116018964036703.
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碩士國立成功大學
航空太空工程學系碩博士班
100
This thesis employs the modified blade element momentum theory, computational simulation, and wind tunnel experiment to analyze and compare respectively the performance rotor blades used in Horizontal-Axis wind turbine (HAWT) and Vertical-Axis wind turbine (VAWT). The Blade element momentum theory is used to predict the rotor performance of HAWT and the adopted double-multiple streamtube model to calculate that of VAWT. For computational simulation, it uses the same turbulent model to simulate the rotors. Furthermore, the performance of the rotor is obtained through the experiments rotor rotation speed, output torque and current and voltage from the generator in terms of the wind speed at various tip speed ratio. It can identify the optimum operation regions of both wind turbines via experiment. Results indicate that the torque output of both wind turbines obtained has almost the same range between 0.3 to 0.4 N-m in experiment under the wind speed of 8 m/s. The maximum torque of VAWT is at TSR of 0.5 while that of HAWT is at TSR of 3.5. The maximum power of HAWT is about 30 watt, which is 6 times larger than VAWT. In addition, the power coefficient of HAWT is about 5 times larger than VAWT, which means that the HAWT has much higher ability to extract the energy in wind than the VAWT. These results are also verified by the modified BEM theory and CFD simulation.
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Lee, Nian-Ze, and 李念澤. "Aerodynamic and Aeroacoustic Prediction of a Horizontal-Axis Wind Turbine." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/08361964798117224115.
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碩士國立臺灣科技大學
機械工程系
103
In this study, the full-scale numerical simulations are performed at rated wind velocity (11.4 m/s) and rated rotor speed (12.1 rpm). The aerodynamic and aeroacoustic prediction of a NREL 5MW offshore wind turbine is performed via a Fluid-Structure Interaction (FSI) approach. The Navier–Stokes equations are used to describe the incompressible and viscous flow around the wind turbine. A k- model is adopted to take the turbulence effects of wind into account. This study used a finite volume method to discretize the governing equations. The FWH model is employed to convert the velocity and pressure change of the flow field into the sound pressure level to determine the noise characteristics. In the simulation, Abaqus is used to calculate the structure deformation of blades, whereas STAR-CCM+ is employed to simulate the flow field. With the calculation switching between Abaqus and STAR-CCM+, the stable position of deformed blades can be obtained. The power decreases about 2.35% for flexible blades when compared with that of rigid blades. The change of total sound level is not obvious between flexible and rigid blades when the detecting point is 15m behind the wind turbine. The total sound level of the flexible blade is about 10% higher than that of the rigid blade when the detecting point is 125m behind the wind turbine.
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Kendall, David Arthur. "Hinged blade model dynamics for a horizontal axis wind turbine." 2003. https://scholarworks.umass.edu/dissertations/AAI3110510.
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This dissertation describes fundamental extensions to the hinge-spring model used to simulate the first mode of blade vibration in wind turbine dynamics. Complete equations of motion are developed while allowing for both bending of the blade perpendicular to its chord and overall motion of the rotor in azimuth and yaw. The model examines the relationship between the natural rotation frequency of the rotor ω and the fundamental natural bending frequency of the blades without including the bending frequency of the tower. In the case of no yaw motion, perturbation analysis and iteration lead to analytical solutions for the bending and azimuth equations of motion that involve as little simplification of these equations as possible. The natural bending frequency is “stiffened” by the rotor rotation and is expressed as a multiple of the rotor rotation, ω∗ ω. While the bending frequency is used in models using the hinged blade, the solutions found in this work contain more detail than can be found in prior investigations. These analytical solutions reveal that the harmonics with frequencies Nω∗ω (ω ∗ + 1)ω and (ω∗ − 1)ω are involved with the coupling between bending motion and azimuth motion with N = 1, 2, 3,…. Subsequent derivation of the power output for the condition of a relatively large amplitude of blade vibration predicts a noticeable contribution to power generation for the ω∗ ω response, which is verified in the data. Glauret's momentum transfer theory as extended by Wilson and Lissaman [1974] and de Vries [1979] is modified to allow for blade bending, variations of wind speed with time and position, and variations in wind direction with time. No vertical wind is considered. It is concluded that: (1) the bending frequency and linear combinations with the rotor rotation frequency provide an important contribution under at least some of the expected operating conditions of the turbine, (2) the dynamic mass imbalance produced by the effects of blade bending is not important for an otherwise balanced rotor, and (3) modest non-symmetric effects to the dynamics such as basic wind shear or changing wind speed and direction enhance the Nω frequencies much more readily than the Nω∗ω frequencies.
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Jian, Ming-Yan, and 簡名硯. "Research and Development of Small Horizontal-axis Wind Turbine System." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/28077900731736239826.
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碩士淡江大學
航空太空工程學系碩士班
99
This thesis is concerned with the research and development of a small horizontal-axis wind turbine system for moving vehicles. Specifically, this study investigates the characteristics matching problems between the rotor blade and generator, and develops a generator output control system using a micro-controller. The characteristics of some available generators are tested using a generator test bench. These generators are combined with the existing rotor blades to evaluate the matching availability. The controller designed of this system uses a microchip PIC16F917 to control the core through the planning and controlling software, with the boost and buck converter module circuit, to achieve objectives of maximum power tracking, charging control and generator overload protection. The design of the controller system from the study, applying to constant voltage of 13V for providing lead-acid battery to charge and provides 12V and 5V USB-type connector for DC electricity outputs, by using experiment and implementation to test and verify feasibility. When installing the wind turbine in vehicles, the wind turbine starts generating electricity with vehicle moving, and providing battery charge ability is able to extend the endurance of electrical vehicles. The 12V electricity output can be used to electronics, while the 5V USB-type electricity output can be used for charging the cell phone, led light, and so on. These enhance the usefulness and convenience of small wind turbines to achieve the goal of green energy saving.
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Gao, Shi-Han, and 高詩涵. "Canard for horizontal axis wind turbine application and Taguchi method analysis." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/65p25w.
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McWilliam, Michael Kenneth. "Development of a Wind Tunnel Test Apparatus for Horizontal Axis Wind Turbine Rotor Testing." Thesis, 2008. http://hdl.handle.net/10012/4075.
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Currently, wind energy presents an excellent opportunity to satisfy the growing demand without the supply and environmental problems associated with conventional energy. The engineering in wind turbines is not fully mature. There are still phenomenon, particularly dynamic stall, that cannot accurately be modeled or controlled. Dynamic stall contributes to fatigue stress and premature failure in many turbine components. The three dimensionality of dynamic stall makes these structures unique for wind turbines. Currently, flow visualization of dynamic stall on a wind turbine rotor has not been achieved. These visualizations can reveal a lot about the structures that contribute to dynamic stall.
Particle Image Velocimetry (PIV) is a powerful experimental technique that can take multiple non-intrusive flow measurements simultaneously of planar flow. Using high-speed cameras time resolved PIV can reveal the transient development of a given flow field. This technique is ideally suited to gain a better understanding of dynamic stall. A custom wind turbine is being built at the University of Waterloo to allow such measurements on the blade. A high speed camera is mounted on the hub and will take measurements within the rotating domain. Mirrors are used so that laser illumination rotates with the blade. The wind turbine will operate in controlled conditions provided by a large wind tunnel. High speed pressure data acquisition will be used in conjunction with PIV to get an understanding of the forces associated with the flow structures. Computational fluid dynamics was used to size the rotor within the wind tunnel. Laser based measurements required special considerations for stiffness.
Many revealing experiments will be made possible by this apparatus. First, the flow structures responsible for the various forces can be identified. Quantitative measurements of the flow field will identify the development of the stall vortex. The quantified flow structures can be used verify and improve models. The high spatial resolution of PIV can map the three dimensional flow structure in great detail. The experimental apparatus is independent of the blade geometry, as such multiple blades can be used to identify the effect of blade geometry. Finally flow control research in the field of aviation can be applied to control dynamic stall.
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周克剛. "Numerical Performance Analysis of a Horizontal-Axis Wind Turbine with Different Wind-Lens Design." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/v3qap6.
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碩士逢甲大學
智能製造與工程管理碩士在職學位學程
107
Taiwan has an excellent wind field that is not inferior to Europe. Taking the Miaoli wind field as an example, its average wind speed is about 8~10 m/s, so it is quite suitable for the development of wind power. According to the theory proposed by Betz in 1919, the maximum operating efficiency of a horizontal-axis wind turbine is 59.3%, so how to increase the output power of wind turbines in the same environment is a subject worthy of investigation. In view of this, Ohya & Karasudani of Kyushu University in Japan proposed wind-lens technology in 2010, using the low-pressure zone of the vortex generated by the introduction of the win-lens to accelerate the airflow through the wind-lens turbine, thereby achieving the goal of increasing output power of a horizontal-axis wind turbine. Since the turbine blades account for 15%~20% of the cost of the wind turbine, this study attempts to employ a low-cost two-blade horizontal-axis wind turbine applied with the wind-lens technology, and numerically analyzes the influence of different configurations of wind-lens on the flow field of the wind-lens turbine and their corresponding output power by using commercial software Ansys CFX. The design parameters discussed include the ratio of the length of the wind-lens to the inner diameter of the wind-lens (Lt/D), the ratio of the height of the wind-lens brim to the length of the wind-lens (h/Lt), the angle of the wind- lens brim (φ), the number of blades and the tip speed ratio (λ), etc. Comparing the numerical simulation results of the bare and the wind-lens turbine, it was found that the more severe the airflow velocity difference inside the wind-lens, the greater the pressure difference downstream of the wind-lens and the greater the vortex intensity generated downstream of the wind-lens, can create the stronger airflow speed, and then the higher output power of the wind-lens turbine can be achieved. This study also attempts to simultaneously adopt five parameters (Lt/D = 0.07, r = 1.42, φ = 0°, Blade = 3, λ = 4.12) that have a positive impact on the wind-lens turbine output power to analyze its performance. It shows that the output power of the wind-lens turbine can be improved by 78.27% compared with the two-blade bare wind turbine. At the same time, this study also found that when the ratio of the free-stream speed to the wind speed downstream of the win-lens turbine (z=-0.19 m) is closest to Betz’s theory U/U1=1/3, the turbine performance is the best. If U/U1 is too high or too low, it will reduce its performance.