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Due to the increase of rotor size in horizontal axis wind turbine (HAWT) during the past 25 years in order to achieve higher power output, all wind turbine components and blades in particular, have to withstand higher structural loads. This upscalingproblem could be solved by applying technologies capable of reducing aerodynamic loads the rotor has to withstand, either with passive or active control solutions. These control devices and techniques can reduce the fatigue load upon the blades up to 40% and therefore less maintenance is needed, resulting in an important money savings for the wind farm manager. This project consists in a study of load control techniques for offshore wind turbines from an aerodynamic and aeroelastic point ofview, with the aim to assess a cost effective, robust and reliable solution which could operate maintenance free in quite hostile environments. The first part of this study involves 2D and 3D aerodynamic and aeroelastic simulations to validate the computational model with experimental data and to analyze the interaction between the fluid and the structure. The second part of this study is an assessment of the unsteady aerodynamic loads produced by a wind gust over the blades and to verify how a trailing edge flap would influence the aerodynamic control parameters for the selected wind turbine blade., På grund av ökningen av rotorstorleken hos horisontella vindturbiner (HAWT) under de senaste 25 åren, en design som har uppstod för att uppnå högre effekt, måste alla vindkraftkomponenter och blad stå emot högre strukturella belastningar. Detta uppskalningsproblem kan lösas genom att använda metoder som kan minska aerodynamiska belastningar som rotorn måste tåla, antingen med passiva eller aktiva styrlösningar. Dessa kontrollanordningar och tekniker kan minska utmattningsbelastningen på bladen med upp till 40 % och därför behövs mindre underhåll, vilket resulterar i viktiga besparingar för vindkraftsägaren. Detta projekt består av en studie av lastkontrolltekniker för havsbaserade vindkraftverk ur en aerodynamisk och aeroelastisk synvinkel, i syfte att bedöma en kostnadseffektiv, robust och pålitlig lösning som kan fungera underhållsfri i tuffa miljöer. Den första delen av denna studie involverar 2D- och 3D-aerodynamiska och aeroelastiska simuleringar för att validera beräkningsmodellen med experimentella data och för att analysera interaktionen mellan fluiden och strukturen. Den andra delen av denna studie är en bedömning av de ojämna aerodynamiska belastningarna som produceras av ett vindkast över bladen och för att verifiera hur en bakkantklaff skulle påverka de aerodynamiska styrparametrarna för det valda vindturbinbladet.

Due to the increase of rotor size in horizontal axis wind turbine (HAWT) during the past 25 years in order to achieve higher power output, all wind turbine components and blades in particular, have to withstand higher structural loads. This upscalingproblem could be solved by applying technologies capable of reducing aerodynamic loads the rotor has to withstand, either with passive or active control solutions. These control devices and techniques can reduce the fatigue load upon the blades up to 40% and therefore less maintenance is needed, resulting in an important money savings for the wind farm manager. This project consists in a study of load control techniques for offshore wind turbines from an aerodynamic and aeroelastic point ofview, with the aim to assess a cost effective, robust and reliable solution which could operate maintenance free in quite hostile environments. The first part of this study involves 2D and 3D aerodynamic and aeroelastic simulations to validate the computational model with experimental data and to analyze the interaction between the fluid and the structure. The second part of this study is an assessment of the unsteady aerodynamic loads produced by a wind gust over the blades and to verify how a trailing edge flap would influence the aerodynamic control parameters for the selected wind turbine blade., På grund av ökningen av rotorstorleken hos horisontella vindturbiner (HAWT) under de senaste 25 åren, en design som har uppstod för att uppnå högre effekt, måste alla vindkraftkomponenter och blad stå emot högre strukturella belastningar. Detta uppskalningsproblem kan lösas genom att använda metoder som kan minska aerodynamiska belastningar som rotorn måste tåla, antingen med passiva eller aktiva styrlösningar. Dessa kontrollanordningar och tekniker kan minska utmattningsbelastningen på bladen med upp till 40 % och därför behövs mindre underhåll, vilket resulterar i viktiga besparingar för vindkraftsägaren. Detta projekt består av en studie av lastkontrolltekniker för havsbaserade vindkraftverk ur en aerodynamisk och aeroelastisk synvinkel, i syfte att bedöma en kostnadseffektiv, robust och pålitlig lösning som kan fungera underhållsfri i tuffa miljöer. Den första delen av denna studie involverar 2D- och 3D-aerodynamiska och aeroelastiska simuleringar för att validera beräkningsmodellen med experimentella data och för att analysera interaktionen mellan fluiden och strukturen. Den andra delen av denna studie är en bedömning av de ojämna aerodynamiska belastningarna som produceras av ett vindkast över bladen och för att verifiera hur en bakkantklaff skulle påverka de aerodynamiska styrparametrarna för det valda vindturbinbladet.

[ES] Esta investigación se centra en el estudio numérico de los efectos no estacionarios de ráfagas de viento sobre el comportamiento aerodinámico de alas de micro-drones. Se estudiaron la estructura del flujo, así como la evolución de la sustentación no estacionaria con respecto a la sustentación cuasi-estacionaria a bajos número de Reynolds y frecuencias reducidas. Se evaluaron la aplicabilidad y las limitaciones de la Teoría de Greenberg para los casos mencionados en 2D. Para ello, se realizaron una serie de Direct Numerical Simulations no estacionarias. Esto mostró que los efectos viscosos predominan a los bajos números de Reynolds que fueron posibles estudiar debido a las limitaciones de la DNS. Así pues, se concluyó que los efectos no estacionarios observados en las simulaciones no se pueden extrapolar a casos reales y experimentales a mayor número de Reynolds., [EN] This research project focuses on the numerical study of the unsteady effects of longitudinal wind gusts on the aerodynamic performance of micro-drone wings. The flow structure and the unsteady-to-quasi-steady lift ratio evolution were studied at low Reynolds numbers and reduced frequencies. The applicability and limitations of Greenberg s Theory were assessed in such 2D cases. A series of unsteady Direct Numerical Simulations were performed in order to do so. This showed that viscosity effects are too dominant at the low Reynolds numbers which were possible to simulate through DNS and thus that the unsteady effects observed in the simulations cannot be extrapolated to the experimental high Reynolds number case.

[ES] Esta investigación se centra en el estudio numérico de los efectos no estacionarios de ráfagas de viento sobre el comportamiento aerodinámico de alas de micro-drones. Se estudiaron la estructura del flujo, así como la evolución de la sustentación no estacionaria con respecto a la sustentación cuasi-estacionaria a bajos número de Reynolds y frecuencias reducidas. Se evaluaron la aplicabilidad y las limitaciones de la Teoría de Greenberg para los casos mencionados en 2D. Para ello, se realizaron una serie de Direct Numerical Simulations no estacionarias. Esto mostró que los efectos viscosos predominan a los bajos números de Reynolds que fueron posibles estudiar debido a las limitaciones de la DNS. Así pues, se concluyó que los efectos no estacionarios observados en las simulaciones no se pueden extrapolar a casos reales y experimentales a mayor número de Reynolds., [EN] This research project focuses on the numerical study of the unsteady effects of longitudinal wind gusts on the aerodynamic performance of micro-drone wings. The flow structure and the unsteady-to-quasi-steady lift ratio evolution were studied at low Reynolds numbers and reduced frequencies. The applicability and limitations of Greenberg s Theory were assessed in such 2D cases. A series of unsteady Direct Numerical Simulations were performed in order to do so. This showed that viscosity effects are too dominant at the low Reynolds numbers which were possible to simulate through DNS and thus that the unsteady effects observed in the simulations cannot be extrapolated to the experimental high Reynolds number case.

[ES] Esta investigación se centra en el estudio numérico de los efectos no estacionarios de ráfagas de viento sobre el comportamiento aerodinámico de alas de micro-drones. Se estudiaron la estructura del flujo, así como la evolución de la sustentación no estacionaria con respecto a la sustentación cuasi-estacionaria a bajos número de Reynolds y frecuencias reducidas. Se evaluaron la aplicabilidad y las limitaciones de la Teoría de Greenberg para los casos mencionados en 2D. Para ello, se realizaron una serie de Direct Numerical Simulations no estacionarias. Esto mostró que los efectos viscosos predominan a los bajos números de Reynolds que fueron posibles estudiar debido a las limitaciones de la DNS. Así pues, se concluyó que los efectos no estacionarios observados en las simulaciones no se pueden extrapolar a casos reales y experimentales a mayor número de Reynolds., [EN] This research project focuses on the numerical study of the unsteady effects of longitudinal wind gusts on the aerodynamic performance of micro-drone wings. The flow structure and the unsteady-to-quasi-steady lift ratio evolution were studied at low Reynolds numbers and reduced frequencies. The applicability and limitations of Greenberg s Theory were assessed in such 2D cases. A series of unsteady Direct Numerical Simulations were performed in order to do so. This showed that viscosity effects are too dominant at the low Reynolds numbers which were possible to simulate through DNS and thus that the unsteady effects observed in the simulations cannot be extrapolated to the experimental high Reynolds number case.

A new methodology is proposed for scaling Doppler lidar observations of wind gusts to make them comparable with those observed at a meteorological mast. Doppler lidars can then be used to measure wind gusts in regions and heights where traditional meteorological mast measurements are not available. This novel method also provides estimates for wind gusts at arbitrary gust durations, including those shorter than the temporal resolution of the Doppler lidar measurements. The input parameters for the scaling method are the measured wind-gust speed as well as the mean and standard deviation of the horizontal wind speed. The method was tested using WindCube V2 Doppler lidar measurements taken next to a 100 m high meteorological mast. It is shown that the method can provide realistic Doppler lidar estimates of the gust factor, i.e. the ratio of the wind-gust speed to the mean wind speed. The method reduced the bias in the Doppler lidar gust factors from 0.07 to 0.03 and can be improved further to reduce the bias by using a realistic estimate of turbulence. Wind gust measurements are often prone to outliers in the time series, because they represent the maximum of a (moving-averaged) horizontal wind speed. To assure the data quality in this study, we applied a filtering technique based on spike detection to remove possible outliers in the Doppler lidar data. We found that the spike detection-removal method clearly improved the wind-gust measurements, both with and without the scaling method. Spike detection also outperformed the traditional Doppler lidar quality assurance method based on carrier-to-noise ratio, by removing additional unrealistic outliers present in the time series.

An extensive study of the mesh requirements when simulating unsteady crosswind aerodynamics for industrial applications is conducted and reported in this article. Detached-Eddy Simulations (DES) of a simple car geometry under headwind, steady crosswind and time-dependent wind gust are analysed for different meshes and flow cases using a commercial software, STAR-CD. The typical Reynolds number of the cases studied is 2.0x106 based on the vehicle length. Mesh requirements for capturing the time development of the flow structures during a gust is provided. While respecting these requirements, the aerodynamic coefficients can be reliably calculated. Using turbulence methods like DES in order to resolve the flow scales provides a significant insight for designing a ground vehicle and, due to the reasonable computational times involved, can be incorporated in a design process in a near future., QC 20101012 Updated from submitted to published., ECO2 crosswind stability and unsteady aerodynamics