Offshore wind power production is an attractive clean energy option, but the difficulty of access can lead to expensive and rare opportunities for maintenance. Smart loads management (controls) are investigated for their potential to increase the fatigue life of damaged offshore wind turbine rotor blades. This study will consider two commonly encountered damage types for wind turbine blades, the trailing edge disbond (bond line failure) and shear web disbond, and show how 3D finite element modeling can be used to quantify the effect of operations and control strategies designed to extend the fatigue life of damaged blades. Modern wind turbine blades are advanced composite structures, and blade optimization problems can be complex with many structural design variables and a wide variety of aeroelastic design requirements. The multi-level design method is an aeroelastic structural design technique for beam-like structures in which the general design problem is divided into a 1D beam optimization and a 2D section optimization. As a demonstration of aeroelastic design, the multi-level design method is demonstrated for the internal structural design of a modern composite rotor blade. Aeroelastic design involves optimization of system geometry features as well as internal features, and this is demonstrated in the design of a flying wing aircraft. Control methods such as feedback control also have the capability alleviate aeroelastic design requirements and this is also demonstrated in the flying wing aircraft example. In the case of damaged wind turbine blades, load mitigation control strategies have the potential to mitigate the effects of damage, and allow partial operation to avoid shutdown. The load mitigation strategies will be demonstrated for a representative state-of-the-art wind turbine (126m rotor diameter). An economic incentive will be provided for the proposed operations strategies, in terms of weighing the cost and risk of implementation against the benefits of increased revenue due to operation of damaged turbines. The industry trend in wind turbine design is moving towards very large blades, causing the basic design criterion to change as aeroelastic effects become more important. An ongoing 100 m blade (205 m rotor diameter) design effort intends to investigate these design challenges. As a part of that effort, this thesis will investigate damage tolerant design strategies to ensure next-generation blades are more reliable.

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 inputs / power 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.

Wind energy, one of the most promising sources of clean energy, has developed rapidly over the last two decades. Wind turbines (WT) are arguably clean during operation, offering minimal pollution and zero CO2 emissions, but significant amounts of energy are used and CO2 emitted during their manufacture, and, furthermore, the turbines are environmentally problematic at end-of-life (EoL), especially the blades. WT blades are mainly made with composite materials comprising thermosetting resin and glass fibre. They are lightweight and strong but problematic to recycle. Large volumes of waste will be generated when these WT blades are decommissioned and environmental concerns have been raised. The main aim of this study is to understand the environmental impact of wind turbine blades and to find solutions to reduce it. A quantitative method is adopted, first evaluating the WT blade waste inventory then calculating its environmental impact, and finally analysing the differences between all possible EoL options in terms of environmental and financial performance. The results firstly identify the global wind turbine blade waste inventory with detailed generation time and location which could help policy makers to gain an understanding of the size and severity of this problem. Secondly, the outputs indicate where most impact is generated and identify what to prioritise to reduce waste and reduce environmental impact, which is of value to blade manufacturers and other stakeholders. Moreover, this work highlights previous incorrect assumptions and provides findings to build on for future work. Thirdly, ‘optimal’ EoL options for the WT blade waste have been characterized: the current ‘optimal’ EoL option is life extension; mechanical recycling is the current ‘optimal’ recycling option; chemical recycling will be the ‘optimal’ option for the future. Future research is suggested as aiming to improve the performance of recycled fibre or to reduce the energy consumption of recycling processes.

The Wind Turbine industry continues to drive towards high market penetrationand profitability. In order to keep Wind Turbines in field for as long as possiblecomputational analysis tools are required. The open source tool QBlade[38] softwarewas extended to now contain routines to analyse the structural properties of WindTurbine blades. This was achieved using 2D integration methods and a Tapered Euler-Bernoulli beam element in order to find the mode shapes and 2D sectional properties.This was a key step towards integrating the National Renewable Energy LaboratoriesFAST package[32] which has the ability to analyse Aeroelastic Responses. The QFEMmodule performed well for the test cases including: hollow isotropic blade, rotatingbeam and tapered beam. Some improvements can be made to the torsion estimationof the 2D sections but this has no effect on the mode shapes required for the FASTsimulations.

No description available.

During the operation of a gas turbine, ingested contaminants present in the air form deposits on the surfaces of the turbine blades. These deposits grow over time, resulting in an increasingly rough surface. This gradual increase in roughness results in several negative consequences, among which is an increase in the rate of heat transfer to the blade which shortens blade life. This thesis presents research in which deposits were evolved on three different turbine blade coupons and their evolution was studied. A trend in roughness change over time was discovered. Also, an attempt was made to find the effect of the deposits on the heat transfer characteristics of a coupon surface. The deposits were formed using the BYU Turbine Accelerated Deposition Facility (TADF), which was used to simulate three months of deposition within a two hour test time. All three coupons underwent four cycles in the TADF: eight total hours of combustor testing—or one simulated year of deposition—with topological measurements being made on the coupon surface after every two hours (three simulated months) of testing. The data produced by the topological measurements were used with a CNC mill to machine scaled-up plastic models of the rough surfaces: four surfaces per model representing three, six, nine, and twelve simulated months of deposition. The models were placed in a wind tunnel where, following a period of thermal soaking at room temperature, they were suddenly exposed to a heated air stream. The thermal histories of the model were recorded with an infrared camera and were used to derive the heat transfer coefficient of each surface using the method developed by Shultz and Jones. The heat transfer coefficients are reported in the form of Stanton numbers to allow for the difference in thermal properties between the conditions and properties of the wind tunnel and its components and those of a real gas turbine. The Stanton numbers for the various surfaces were plotted versus the simulated gas turbine operational time. Additionally, several roughness correlations were used to predict the Stanton number for each surface, producing a probable Stanton number history for the coupon. The measured nondimensional heat transfer coefficients did not reach the magnitudes predicted by the correlations. This is most likely due to unexpected flow conditions inside the wind tunnel. Recommendations for future research are presented.

No description available.

Large wind turbine blades, manufactured from fibre reinforced laminated composite materials, are key structural components of wind turbine systems. The demands for efficient and accurate modelling techniques of these composite blades have significantly increased. Over past decades, although complex computational models have been widely developed, more analytically based models are still very much desired to drive the design and optimization of these composite blades forward to be lighter, stronger, efficient and durable. The research work in this thesis aims to develop such more analytically based aerodynamic, structural and aero-elasticity models for large wind turbine blades manufactured from fibre reinforced laminated composite materials. Firstly, an improved blade element momentum (BEM) model has been developed by collectively integrating the individual corrections with the classic BEM model. Compared to other existing models, present BEM model accounts for blade tip and root losses more accurately. For laminar flow, the 3-D cross-flow is negligibly small. In this case, present BEM model with statically measured 2-D aerodynamic coefficients agrees closely to experimental measurements. However, stall delay correction is required for a 3-D rotating blade in stall. A new stall delay model is developed based on Snel s stall delay model. Verifications are performed and discussed for the extensively studied NREL UAE phase-VI test. The predictions of distributive and collective factors, e.g. normalised force coefficients, shaft torque and etc. have been compared to experimental measurements. The present BEM model and stall delay model are original and more accurate than existing models. Secondly, significant deficiency is discovered in the analytical thin-walled closed-section composite beam (TWCSCB) model proposed by Librescu and Vo, which is widely used by others for structural modelling of wind turbine blades. To correct such deficiency, an improved TWCSCB model is developed in a novel manner that is applicable to both single-cell and multi-cell closed sections made of arbitrary composite laminates. The present TWCSCB model has been validated for a variety of geometries and arbitrary laminate layups. The numerical verifications are also performed on a realistic wind turbine blade (NPS-100) for structural analysis. Consistently accurate correlations are found between present TWCSCB model and the ABAQUS finite element (FE) shell model. Finally, the static aero-elasticity model is developed by combining the developed BEM model and TWCSCB model. The interactions are accounted through an iterative process. The numerical applications are carried out on NPS-100 wind turbine. The numerical results show some significant corrections by modelling wind turbine blades with elastic coupling.

Methods of determining natural frequencies of the D76D88, B76D88, A86E93, C86G90, C86L90 and C125L89 turbine wheel designs for various environmental conditions were investigated by application of Finite Element Analysis and beam theory. Modelling and simulation methods were developed ; the first method composed of 15 finite element simulations ; the second composed of 15 finite element simulations and a set of experimental frequency survey results; the third composed of 5 simulations , an incorporated mathematical model and a set of experimental frequency survey results. Each of these methods was designed to allow prediction of resonant frequency changes across a range of exhaust gas temperature and shaft rotational speed. For the new modelling and simulation methods, an analysis template and a plotting tool were developed using Microsoft Excel and MATLAB software. A graph showing a frequency-temperature-speed variations and a Campbell Diagram that incorporates material stiffening and softening effects across a range of rotational speeds was designed, and applied to the D76D88, B76D88, A86E93, C86G90, C86L90 and C125L89 turbine wheel designs. New design methodologies for turbine wheels were formulated and validated, showing a good agreement with a range of data points from frequency survey, strain-gauge telemetry and laser tip-timing test results. The results from the new design method were compared with existing single compensation factor methodology, and showed a great improvement in accuracy of prediction of modal vibration. A new nomenclature for the mode shapes of a turbocharger’s blade was proposed, designed and demonstrated to allow direct identification of associated mode shape. It is concluded that Finite Element Analysis combined with the frequency survey is capable of predicting changes in turbine natural frequencies and, when incorporated into the existing turbine design methodology, resulted in a major improvement in the accuracy of the predictions of vibration frequency.

Bakgrunden till projektet är problem med kanterosion av turbinblad inom vindkraftverks- industrin. Det är ett fenomen som uppstår när turbinblad roterar i höga hastigheter och träffar partiklar, främst vattendroppar i regn. Denna erosion skadar turbinbladen, vilket både minskar vindkraftverkens effektivitet och sprider partiklar i den lokala miljön. För att både undersöka detta fenomen och ge möjlighet att utvärdera olika materials motståndskraft mot erosion ska en testrigg tas fram. Utöver detta ska testriggen även möjliggöra uppsamling av partiklar för vidare forskning kring deras effekt på miljön. Som utgångspunkt används en tribometer med rotationsmekanism från ett föregående maskinkonstruktionsprojekt på KTH. Ombyggnationen av denna avgränsas till att endast genomföras digitalt med hjälp av CAD för att hålla mängden arbete till en rimlig nivå. Förutom CAD har arbetet även inkluderat kravspecifikationer, beräkningar i MATLAB, FEA-analyser och kostnadskalkyler. Resultatet är en digitalt styrd testrigg med tillhörande komponentlista och instruktioner för tillverkning och genomförande. Inköpskostnad för ombyggnationen uppskattas till 28 000 kr. Riggen för en cylindrisk provbit genom ett artificiellt regn i hög hastighet, vilket resulterar i en accelererad nötningsprocess. Under testets gång dokumenteras erosionen visuellt med hjälp av en kamera och efter testet kan mängden förlorat material mätas i vikt och partiklar samlas upp. Flera andra parametrar dokumenteras automatiskt under testets gång för att ge en mer detaljerad bild av processen och data för undersökningar av repeterbarhet. Slutligen konstateras att testriggen uppnår alla krav ställda på den förutom att den inte har en nödbroms. Avsaknaden av nödbroms diskuteras och det leder till slutsatsen att testriggen, även utan nödbroms, är fullt fungerande, enkel och säker att använda. / The background for this project is a problem in the wind turbine industry, namely leading edge erosion of turbine blades. This occurs when wind turbine blades rotate at high speeds and collide with particles, mainly water drops in rain. This erosion damages the turbine blades, reducing the efficiency of the wind turbines and releasing particles into the local environment. To investigate this phenomenon and evaluate the durability of different materials, a test rig is to be developed. In addition, the test rig will enable the collection of particles to facilitate further research into their environmental impact. A tribometer with a rotation mechanism from a previous project at KTH serves as the starting point. The reconstruction of this tribometer is limited to a digital implementation using CAD to keep the amount of work at an appropriate level. In addition to CAD, the work has also included requirements specifications, calculations in MATLAB, FEA, and cost estimates. The result is a digitally controlled test rig with an accompanying component list and instructions for manufacturing and implementation. The estimated purchase cost for the reconstruction is 28,000 SEK. The rig tests a cylindrical sample by propelling it at high speed through artificial rain, resulting in an accelerated wear process. The erosion is visually documented using a camera during the test. Afterwards the amount of lost material can be measured by weight and the particles collected. Several other parameters are automatically recorded during the test to provide a more detailed picture of the process and data for investigations into repeatability. Finally, it is concluded that the test rig meets all its requirements except for the absence of an emergency brake. The absence of an emergency brake is discussed, leading to the conclusion that despite missing an emergency brake, the test rig is fully functional, easy to use, and safe.