Tg Teknikgruppen

This project will investigate and develop software for the prediction of aerodynamic rotor-tower interactions which occur when the rotor-blades of a Horizontal Axis Wind Turbine interact with the disturbed velocity field of the tower. This project will study both upwind and downwind rotor cases. The objectives of the project are: - to quantify the extent of the aerodynamic effect of the tower on the rotor blades, - to develop accurate methods which are suitable for use by the industry to predict the effect, - to study means of alleviating the effect. The project will focus on stall controlled rotors since the major uncertainties occur in or near the stall regime. The technical approach to the study will link fundamental experiments, computational fluid dynamics, engineering models and validation by data obtained from operating HAWTs in the field. It will be carried out by a consortium of partners in five EU countries covering manufacture, operation, government and academic research. Experimental measurements of blade pressures and forces and of the disturbed velocity fields for both both two- and three-dimensional models of the interaction will be obtained at reduced scale from wind tunnel tests, in the latter case using a model twin-bladed turbine, and at full scale by analysis of blade pressure and force data from an instrumented 27m diameter twin-bladed turbine in the field. Existing Navier-Stokes (CFD) codes, (a) using primitive variables, (b) using a vortex basis will be developed to handle the interaction aerodynamics between a moving rotor and the fixed tower, first at model scale and then at full scale. The blade surface pressure and wake velocity data will be used to aid the development and validation of these codes. Engineering codes will be further developed and tuned against the CFD codes to incorporate rotor-tower interaction and then tested against measured loads from operating wind turbines. Two types of machine will be monitored for these tests, a series of similar machines having a 40m diameter upwind rotors and a prototype full scale machine having a highly flexible downwind rotor. An experimental (wind tunnel) study will be carried out into the effect of tower wake suppression or modification devices, such as strakes, fairings and tower porosity, on the strength of the interaction between rotor and tower for both upwind and downwind turbine cases. The achievements of the project, in order of importance, will be: development and dissemination to the wind turbine industry of improved engineering codes able to predict with greater reliability the magnitude and effects of the rotor-tower interaction, adapted CFD codes capable of simulating blade tower interaction, detailed experimental data on blade-tower interaction, including data documenting the effectiveness of devices which by acting on the tower flow or its wake reduce or suppress the interaction, documentation of the ways in which blade-tower interaction can occur together with an improved understanding of the phenomenon, which should feed into future wind turbine designs.

Objectives To examine the total design envelope criteria of existing selected Wind Turbines for complex terrain operation (Stall 100kW-600kW, Pitch 225kW-500kW, Variable Speed 100kW-450kW, and Teeter 1000kW concepts) in relation to the IEC-1400-1 standard, the wind climate and the complex terrain wind structure; and to investigate the potential for increase in WT energy production and/or decrease in loading that can be attained through feasible WT adaptations; i.e. to investigate the potential ranges and means of cost reduction for the wind produced electricity in very high wind speed complex terrain sites. To fully investigate the newest and state of the art rotor designs for selected Stall and Pitch WTs operating on highly complex terrain sites with very high wind speeds and to examine the possibility of control parameters optimization for the Stall, Pitch, Variable Speed and Teeter WTs for the same sites, with the objective to increase WT energy production and/or decrease loading. To implement the findings of the R&TD work on selected operational Stall, Pitch and Variable Speed WTs (construction, installation and operation of the new rotors and possibly optimized controller parameters) operating on highly complex terrain sites exhibiting high wind speeds and to operate the adapted machines for a minimum of one year. To fully quantify and verify the performance of the adapted Stall, Pitch and Variable Speed WTs through detailed wind, load, power and machine condition measurement programs on the adapted WTs and to provide definite conclusions on the kWh cost reductions attainable. Technical approach The project will integrate all relevant information gathered within the previous complex terrain oriented projects where the differences between the complex and flat terrain wind structure were established, i.e. it will use and enhance the scope of the newly developed 3D fully coupled complex terrain wind turbulence model (CTTM). This information will be enriched with the investigation of the total design envelope (wind climate, extremes, transients, grid, etc.) and with the results of the measurements from the application of the new state of the art rotors to the selected Stall and Pitch WTs. Detailed wind, machine power and loading measurements (CRES, RISO, TG) will be used in parallel to the application of advanced parameter identification techniques (PI) to the measurement databases and to the advanced state of the art computational tools and WT models (CRES, NTUA, RISO, TG) in the full design envelope investigation as it relates to the IEC-1400-1, the wind climate and the complex terrain wind, and in the kWh cost reduction assessment. The new state of the art rotors (stall and pitch) will be installed and operated on selected WTs in Greece and Spain (CRES, RISO) on high speed complex terrain sites. The rotors will be redesigned and constructed to match the specific characteristics of the WTs to be installed on and will be monitored for a minimum of a year. Full WT measurement programs (wind, power, condition) will be performed on the adapted WTs in order to produce the full performance map of the new rotors. Finally the findings from the operation of the new rotors will be evaluated against the results of the design envelope investigation and guidelines regarding the adaptation techniques towards WT kWh cost reduction for the different control strategies will be provided. Expected achievements and exploitation Databases for complex terrain wind and wind climate characterization along with databases for WT performance and loading. A methodology for the full design envelope assessment of WTs for complex terrain operation, and guidelines for the inclusion of the relevant to WT design complex terrain characteristics in the design standards developing world-wide. Reduced costs of wind energy production through identification of means and ways of increasing energy production and decreasing loading for WTs operating on very windy complex terrain sites. New rotor designs for stall and pitch WTs and optimization of WT control parameters for very high wind speed operation in complex terrain sites, targeted and expected to reduce the kWh cost of Stall and Pitch WTs by 5%.

OBJECTIVES OF THE PROJECT: The European wind industry uses wind turbine analysis codes for the calculation of dynamic loads and energy yield. These codes consist among others of a wind simulator and an aeroelastic model. The results of these codes are important for the design of wind turbine (components) and for certification purposes. In Europe different codes are used which are developed by several organisations. The level of confidence the industry and the certification institutes may have in these codes is unknown. The objectives of the project are: - To assess the accuracy and reliability of the most widely used European wind turbine design codes for improved support of wind turbine design and certification; - To define recommendations for improvement of the present wind turbine design codes and the required supporting experiments. TECHNICAL APPROACH: An overall verification of the most widely used European wind turbine codes is performed. Eight wind turbine codes from five different countries (Denmark, Greece, Great Britain, Netherlands and Sweden) will be involved. Code predictions of mechanical loads (blade loads, rotor loads and tower loads) will be compared with a reference set of high quality experimental data on modern wind turbines. The measurements are obtained at different conditions (normal operating conditions and special events). The experiments will be performed on three different wind turbines (WindMaster 600, Nordtank 500 and Tacke 500) with three different control strategies (stall regulated, pitch regulated and variable speed in combination with free yaw). The diameter of the turbines range between 37 and 48 m. The turbines are considered to be representative for the present and future generation of wind turbines EXPECTED ACHIEVEMENTS - The present verification project gives insight into the performance of the different state of the art wind turbine codes. On basis of this insight the wind energy industry can make well-founded decisions on the use and the selection of codes for the design process. - The project results form a basis for the determination of more accurate partial load factors, or other safety margins which account for the uncertainty in the results from load calculations. This enables the wind energy industry to design more reliable wind turbines or to reduce weight and costs of wind turbine (components). - From the objected recommendations on code improvements more reliable and accurate codes can bedeveloped for future improvement of industrial products. - The measurements are stored in a data base on CD-ROM and a WWW-site. Then they can be used in future projects to validate new or modified wind turbine codes. - European certification institutes can assess results determined with known and verified codes more efficiently. This yields lower certification costs for the industry and accelerates procedures and the time to market introduction.

Objectives The project aims to contribute to the technical harmonization of the European wind turbine market by two means: - Development of guidelines and recommendations on technical issues on wind energy technology, which are not covered by existing draft tandards, or criteria which are crucial for European harmonization. They will be applicable by standardisation bodies (CEN/CENELEC, IEC), wind turbine designers and certification institutes. - Implementation of a network of measurement and testing institutes in which uniform methods and procedures are used. This EUREC Agency MEASNET organization guarantees high quality measurements and mutual acceptance of measurement results. Tehnical Approach The project is a continuation of the Joule II project CT93-0387, which resulted in recommendations for technical guidelines and measuerement practices for the European wind energy industry. This project cover two technical issues, not covered or not sufficiently covered by existing (draft) standards. In addition it includes the implementation of MEASNET, a co-operative organization of wind turbine test institutes, in which uniform, standardized and mutually agreed upon measuring methods are applied. The technical issues chosen are: - Load spectra and extreme wind conditions; - Quantification of failure probabilities; - Integration of blade tests in design; - Power performance in complex terrain; - Site evaluation techniques. The first measurement procedure to be harmonized within MEASNET is anemometer calibration. Additionaly measurement procedures for power performance, noise production and electrical power quality will be dealt with. Expected Achievements and Exploitation As a result of this project European (CEN/CENELEC) and International (IEC) standardization bodies are guided effectively on the way to uniform standards for the wind turbine industry. An EUREC agency MEASNET organization of the main wind turbine test institutes will be in operation, guaranteeing well defined and mutually agreed upon measurement procedures. Internal assessment of quality control will be defined and maintained. A procedure for admission of organizations other than the founding institutes will be effectuated. Practical guidelines and/or status reports on the selected technical issues will be delivered. Information exchange with all relevant parties will be achieved through continuation of the EWTS bulletins, covering the news on the project and on related subjects such as standards and normalisation procedures relevant for the wind turbine industry.

Objectives The objective is to identify and quantify the influence of the complex terrain environment to the HAWT response (loading and power output), in an attempt to investigate existing and propose new, alternative, design aspects for individual components. It will integrate all relevant previous information with new data, aiming to cover the complete range of the state of the art design concepts and sizes, including stall, pitch, variable speed and soft yaw machines, operating at complex terrain sites in Europe and the USA. Technical Approach Detailed wind and machine loading measurements will be used to validate existing numerical models and identify their scope for predicting the complex-terrain-triggered particularities. A combined macro- and micro-wind characteristics experiment, in the vicinity of an existing instrumented machine, will provide added value to the project and permit a detailed cross-check and adaptation of the available numerical tools for wind and wind turbines in complex terrain. These tools and the large experimental data base will be used for the design aspects investigation to produce design guidelines for complex terrain WT operation. The project involves the following steps: - The complex terrain wind macro- and micro- characteristics, i.e. the full wind fetch (3D wind profile) and its turbulent characteristics (rotor wind structure) will be established through existing data, a large scale wind experiment, and wind modeling. - The complex terrain wind macro- and micro- characteristics, will be correlated to the full WT response through existing data from Stall and Pitch WTs, new measurements on stall, pitch, variable speed, soft yaw and large size WTs (100kW - 1000kW), modeling, and design tools validation. - The major parameters of the system Wind-WT and understood in detail and the sensitivity of the system output (power, loads) to the system design parameters (design envelope of the machine) will be studied and quantified for representative wind conditions at a complex terrain environment. A parameter identification methodology will be used with the evaluation of the machine's performance sensitivity to the Wind-WT parameters. - Synthesis to determine, whether machines designed for flat terrains are suitable for complex terrains as well, and whether the complex terrain features can be faced by just trimming existing design concepts or if new design criteria are necessary for individual machines. Expected Achievements and Exploitation The combination of the measurement results (wind and machines) the application of the macro- wind modeling tools and their experimental verification; the application of the micro- wind modeling tools to establish the complex terrain turbulent wind structure; the application of the design/modeling tools on the machines involved in the project; and the application of the PI methodology to the wind-machine measurements with the guidance of the WT manufacturers, is expected to produce the full macro- and micro- complex terrain wind structure effects on the operation, the production and loading of wind turbines in complex terrains and to show any required machine design changes or adaptations. The project results will be made available to CEN/CENELEC to support the European Standards Work.