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Ground acoustic impedance is important in the prediction of sound propagation. In this paper, a new measurement technique is developed based on the Image Source method. Two set-ups are used. Set-up 1 consists of a speaker at a height of 0.5 m and two microphones at heights of 0.2 m (or 0.3 m) and 0.5 m with a separation distance of 1.75 m between the speaker and microphones. Set-up 2 has a double separation distance and almost double heights of 0.5 m and 1 m. The impedance measurements were performed at grass-ground and soft soil-ground after harvest in two different wind farms in Denmark. The findings are: (1) The Nordtest method works in Set-up 1, but gives inconsistent results in Set-up 2. (2) The new method gives consistent results in both set-ups. (3) The flow resistivity obtained with an impedance model can only be used with that specific impedance model, and it becomes inaccurate when used with other impedance models. (4) The determination procedure of flow resistivity is suggested to work with any impedance model. (5) A relation between the flow resistivity obtained with the one-parameter model of Delany and Bazley and that obtained with the four-parameter model of Attenborough is derived.

Unsuitable wind farm layout design influences wind energy conversion efficiency as well as wind farm noise radiation. In the past, more attentions were paid on high energy efficiency wind farm design, but little progress was achieved on noise constrained wind farm optimization. The present work aims at developing a numerical optimization framework that combines the modelling of wind farm wake and wind farm noise with the annual energy production in an optimization algorithm. Firstly, a wind turbine wake model is implemented in the optimization framework to obtain the detailed flow field of a wind farm. Secondly, the noise radiation around a wind farm is simulated with an advanced method based on solving the parabolic wave equation. Thirdly, the annual energy production of a wind farm is calculated with respect to a prescribed wind speed probability distribution. Finally, wind farm layout optimization is carried out with a cost model built on the levelised cost of energy and an efficient iterative approach. According to the results, the developed optimization framework is capable of seeking a trade-off between maximum energy yield and minimum negative environmental effect.

Most of the k − e closures for modeling stratified surface layer are derived from the classical similarity functions and might fail in complex terrain due to limitations of the classical similarity functions. Despite the classical similarity functions to limit the flux Richardson number R f , we present new similarity functions estimated from field measurement in full range of R f and propose a k − e model using the new similarity functions to improve predictions of stratified surface layer flows in complex terrain. Measurements show that the classical similarity functions are partially valid in complex terrain and the wind shear under strongly stable conditions is constrained at large R f . According to numerical studies in two areas of complex terrain, models using the classical similarity functions and the new similarity functions both present good predictions of convective airflows in complex terrain. The new similarity functions are shown to significantly improve the k − e model in predicting stably stratified airflows in complex terrain by constraining the wind shear at large R f , while the classical similarity functions without limiting the wind shear lead to significantly misestimating the wind speedup factor under stable conditions. Using the proposed model to predict flows in wind farm could benefit wind resource estimation and wind power forecasting.

The tip loss is an important phenomenon in wind turbine aerodynamics and has to be modelled separately in the blade element momentum (BEM) method for predicting the wind turbine aerodynamic performance. Instead of following the conventional trend of thought, the present study for the first time regards the interference factors as a summation of two parts. One is determined by the downwash due to the three-dimensional effect and the other is determined by rotation. Two corresponding factors of FS and FR are proposed to represent the effects of the two parts, respectively. This way of consideration implies a new model for the BEM method, providing appropriate tip loss predictions. The new model is validated in BEM computations of the NREL Phase Ⅵ rotor, the Swedish WG 500 rotor, and the NREL 5 MW reference rotor, with a radius of 2.675 m, 5.029 m and 63 m, respectively. It shows a good accuracy in a wide range of tip speed ratios from 1.58 to 11.3, and presents a good robustness in the cases involving high angles of attack and in the cases involving high axial interference factors. That makes the new model attractive for tip loss correction in BEM.

The power generated by a wind turbine largely depends on the properties of wind resource. In this work, wind characteristics in different regimes occurring throughout the idealized diurnal cycle and its impact on wind turbine's power performance are investigated systematically by means of large-eddy simulation (LES), and blade element momentum method (BEM), respectively. Through a precursor simulation of the atmospheric boundary layer (ABL) over a homogenous surface throughout a day, it is found that the resulting shapes of wind profiles (including wind speed, wind direction and turbulence level) vary significantly at different time periods, induced by distinct stabilities of the atmosphere. The simulated wind field data are then applied to a NREL 5 MW wind turbine for its power evaluation. Due to variabilities in wind shear and turbulence, the equivalent (disk-averaged) wind speed is introduced for power prediction. It is found that the magnitude and fluctuation of turbine's diurnal power are closely related to the atmospheric stability. In general, the average power production is higher under convective conditions during the day than under stable conditions at night, with a difference approaching 24.4%. This indicates that wind energy resource assessment will close to reality and benefit from increased accuracy if atmospheric stability impacts are considered for turbine's power predictions.

A new wind farm during its development phase requires a technical evaluation of its annual power prediction and noise issue in the area in and around the wind farm. In this paper, for the first time, an advanced numerical method for wind farm assessment is developed, which consists of a Reynolds averaged Navier-Stokes - Actuator Disc model for the flow modelling, a semi-engineering model for the noise source modelling, and a parabolic wave equation model for the sound propagation modelling. The developed method can evaluate both annual energy production of wind farm and noise emission at receivers nearby. The wind farm considered in this study is located in a typical mountainous area. The energy production of the wind turbines is simulated and compared with measured data. The flow simulations over the complex terrain are performed using the in-house developed Navier-Stokes solver. A wind farm noise map is created by solving the parabolic wave equation. The obtained flow results are the inputs to the parabolic wave equation solver for sound propagation. The numerical computations are performed on a standard high-performance computer cluster. The developed numerical method provides a reliable assessment method for wind farm about its energy efficiency and noise features.

Promising technology for the conversion of cellulose to aromatics by catalytic fast pyrolysis (CFP) was investigated using five zeolite catalysts, i.e., 5A, SAPO-34, HY, BETA and HZSM-5. The relationship between the porosity and acidity of different zeolites with product selectivity was studied. The results showed that both the acidity and pore size of the zeolite significantly affected the production of aromatics and coke, especially the bio-oil composition. The bio-oils obtained over 5A or SAPO-34 (small pore

In order to effectively improve the quality of bio-oil from catalytic pyrolysis (CFP) of sewage sludge (SS) and to produce aromatic-rich bio-oil, the evolution mechanisms of nitrogen and formation of aromatics during CFP of SS over metal-loaded HZSM-5 (HZ) were investigated in depth. The results show that the presence of metals caused the slight decrease in oil-C (carbon in bio-oil) yield and the increase in gas yield and total carbon yield of aromatics. Ni-loaded HZ has a better performance than Co-loaded one in improving the carbon yield of aromatics, while the maximum yield of 11.2% was obtained over 0.5Ni-HZ. Metal-loaded HZ promoted the formation of monocyclic aromatics rather than polycyclic aromatics and Ni significantly enhanced the selectivity of benzene. With the addition of Ni and Co, more nitrogen was released as NH3 or fixed in solids. NH3 yield increased by raising the metal loading, and the highest NH3 yield of 36.8% was obtained over 3.0Ni-HZ. Ni and Co promoted the cracking reactions during CFP to generate more H radicals, which have advantages to the ring-opening of N-containing heterocycles in SS to produce aromatics and NH3. A possible catalytic mechanism of CFP of SS over metal loaded HZ was proposed in this study.

H5 was developed to mesoporous system via alkali treatment, and sulfated zirconia (SZr) modified hierarchical HZSM-5 (AT0.2/H5) catalysts (named AT0.2/SZxH5) were successfully prepared by a series of post-treated method followed by Zr(NO3)4·5H2O and H2SO4 as active component. The innovative approach really enhanced acidity of AT0.2/H5 support, which results from the interaction of the sulfate groups attached to zirconia that doped on MFI framework with silanol groups. Adding active component can not only compensate for the loss of acid sites caused by NaOH treatment, but also re-develop more active sites owing to the formation of SZr. Meanwhile, NH3-TPD showed higher strong acid sites and weak acid sites in AT0.2/SZ6:1H5 than other prepared catalysts. The catalytic activity in converting lignite pyrolysis volatiles to light aromatics, including benzene, toluene, ethylbenzene, xylene and naphthalene (BTEXN), correlates well with the enhanced acidity. Compared with H5, the yield of light aromatics increased significantly from 15.2 to 19.3 mg/g over AT0.2/SZ6:1H5 at 600 °C. According to the characterization of N2 adsorption–desorption, SEM, and XRD, both the S species as SO42− and Z species as ZrO2 improved the textural properties of the support itself. Besides, the molar ratio of S/Zr was in direct proportion to the yield of BTEXN in a certain range, and 6:1 exhibited the optimal catalytic performance. The prepared solid acid catalyst provides a promising strategy to directional prepare light aromatics during lignite catalytic pyrolysis.

Recently, actuator line model become popular in studying wind-turbine wakes. However, existing models ignore or inaccurately describe nacelle effects, which have been shown to pose significantly impact on wakes. To address the physics underlying here, we develop the actuator line model with large-eddy simulation by introducing a new anisotropic body-force projection model. We validate the new model against a field experiment and the validation indicates that the new anisotropic model can predict the wake more precise than the existing isotropic model. Furthermore, we extend the study to wake characteristics under various yaw conditions. The results show that the thrust component normal to the flow direction creates a skewed wake behind the turbine, which in turn promotes the wake transition from the two-peak profile to the one-peak profile. The wake skew exacerbates the instability of the tip vortex and causes the wake region to narrow. At small yaw angles, the nacelle vortex radially diffuses and blends with the tip vortex in the far wake. At large yaw angles, the nacelle vortex intercepts the tip vortex in the near wake due to the different spatial distribution of thrust. It is concluded that the nacelle significantly affects wind-turbine wakes especially during yaw condition.

In order to develop super-large wind turbines, new concepts, such as downwind load-alignment, are required. Additionally, segmented blade concepts are under investigation. As a simple example, the coned rotor needs be investigated. In this paper, different conning configurations, including special cones with three segments, are simulated and analyzed based on the DTU-10 MW reference rotor. It was found that the different force distributions of upwind and downwind coned configurations agreed well with the distributions of angle of attack, which were affected by the blade tip position and the cone angle. With the upstream coning of the blade tip, the blade sections suffered from stronger axial induction and a lower angle of attack. The downstream coning of the blade tip led to reverse variations. The cone angle determined the velocity and force projecting process from the axial to the normal direction, which also influenced the angle of attack and force, provided that correct inflow velocity decomposition occurred.

Noise generated from wind turbines is a big challenge for the wind energy industry to develop further onshore wind energy. The traditional way of reducing noise is to design low noise wind turbine airfoils and blades. A wind turbine operating under wind shear and in yaw produces periodic changes of blade loading, which intensifies the amplitude modulation (AM) of the generated noise, and thus can give more annoyance to the people living nearby. In this paper, the noise emission from a wind turbine under wind shear and yaw is modelled with an advanced fluid-structure-acoustics framework, and then controlled with a pitch control strategy. The numerical tool used in this study is the coupled Navier&ndash, Stokes/Actuator Line model ElliSys3D/AL, structure model FLEX5, and noise prediction model (Brooks, Pope and Marcolini: BPM) framework. All simulations and tests were made on the NM80 wind turbine equipped with three blades made by LM Wind Power. The coupled code was first validated against field load measurements under wind shear and yaw, and a fairly good agreement was obtained. The coupled code was then used to study the noise source control of the turbine under wind shear and yaw. Results show that in the case of a moderate wind shear with a shear exponent of 0.3, the pitch control strategy can reduce the mean noise emission about 0.4 dB and reduce slightly the modulation depth that mainly occurs in the low-frequency region.

Increasing maintenance costs will hinder the expansion of the wind power industry in the coming decades. Training personnel, field maintenance, and frequent boat or helicopter visits to wind turbines (WTs) is becoming a large cost. One reason for this cost is the routine turbine inspection repair and other stochastic maintenance necessitated by increasingly unbalanced figure loads and unequal turbine fatigue distribution in large-scale offshore wind farms (OWFs). In order to solve the problems of unbalanced fatigue loads and unequal turbine fatigue distribution, thereby cutting the maintenance cost, this study analyzes the disadvantages of conventional turbine fatigue definitions. We propose an improved fatigue definition that simultaneously considers the mean wind speed, wind wake turbulence, and electric power generation. Further, based on timed automata theory, a power dispatch approach is proposed to balance the fatigue loads on turbines in a wind farm. A control topology is constructed to describe the logical states of the wind farm main controller (WFMC) in an offshore wind farm. With this novel power control approach, the WFMC can re-dispatch the reference power to the wind turbines according to their cumulative fatigue value and the real wind conditions around the individual turbines in every power dispatch time interval. A workflow is also designed for the control approach implementation. Finally, to validate this proposed approach, wind data from the Horns Rev offshore wind farm in Denmark are used for a numerical simulation. All the simulation results with 3D and 2D figures illustrate that this approach is feasible to balance the loads on an offshore wind farm. Some significant implications are that this novel approach can cut the maintenance cost and also prolong the service life of OWFs.

This paper evaluates the influence of atmospheric stability and topography on wind turbine performance and wake properties in complex terrain. To assess atmospheric stability effects on wind turbine performance, an equivalent wind speed calculated with the power output and the manufacture power curve is proposed and calibrated with the mast hub-height wind speed. After estimating the thrust coefficient and turbulence dissipation, this paper examines wind turbine performance curves and wake profiles segregated by atmospheric stability. Results show that the equivalent wind speed at a given mast wind speed can increase by 2% under stable conditions and decrease by 5% under unstable conditions as compared with that under neutral conditions, yielding about 16% reductions of power output and thrust coefficient from stable conditions to unstable conditions. Due to the lower thrust coefficient and the enhanced turbulence, the wind turbine wakes are found to recover faster under unstable conditions than under other stability conditions. Differences in wind turbine performance and asymmetric wake profiles due to topographic effects are also observed. Results suggest that atmospheric stability and topography have significant influences on wind turbine performance and wake properties. Considering effects of atmospheric stability and topography will benefit the wind resource assessment in complex terrain.

The diurnal variation of atmospheric conditions over land has a significant effect on the wind and temperature distributions which greatly influence the generation and propagation of wind turbine aerodynamic sound. In this paper, a fully consistent unsteady approach is used to study wind turbine noise such that large eddy simulation with a rotational actuator disk wind turbine model is used to model the wind and temperature around a mega-watt scale wind turbine over a diurnal cycle, and time dependent flow and temperature fields are used as input to the coupled wind turbine noise generation-propagation model. Computations are carried out for four different 10 min datasets selected at certain periods of a day for a same hub height wind speed. It is observed that the time dependent as well as the time averaged sound pressure levels in near field do not show large variations during the day. However, as we move away from the turbine, the propagation effects take over and downwind of the turbine the night time levels exceed the day time levels (at 3600 m the averaged difference reaches 6.5 dBA).

It is known that wind turbines actually operate in the lower part of the atmospheric boundary layer (ABL), the modelling of this ABL flow is an important precondition for the simulations of wind turbine wakes. So, the capabilities of various inlet boundary conditions with related modelling methodologies in constructing equilibrium ABL are assessed firstly through cases of ABL flows over uniformly rough terrain, to ascertain that there are no substantial changes in the prescribed profiles throughout the whole computational domain. In this process, six popular turbulence inflow profiles, including four uniform and two non-uniform ones, are considered and investigated. Then, sensitivity studies on inflow profiles for predicting wind turbine wake development are carried out. Through comparing with the Sexbierum field experimental data, in terms of wake velocity and turbulence intensity along the cross-wind direction at several downstream positions, this study finds out that the shape and magnitude of wake velocity and wake turbulence profiles are significantly affected by different inflow profiles. Possible reasons for this sensibility are discussed, and accordingly, some suggestions are given to improve the accuracy of wind turbine wake simulation.

The present review paper provides a comprehensive overview of the research activities on wind turbine aeroacoustics at DTU over the last 20 years, as well as it gives the state-of-the-art of noise prediction models for wind turbines under complex inflow conditions. Various noise generation models developed at DTU are described and analyzed, including models based on the acoustic analogy, flow-acoustics splitting techniques, Amiet's model, and various engineering models. Some of the models are coupled to existing aero-elastic software and computational fluid mechanics models developed at DTU, and implemented in the simulation platform WindSTAR (Wind turbine Simulation Tool for AeRodynamic noise). This simulation platform consists of WindSTAR-Gen, dealing with models for generation of noise and design of low-noise wind turbines, and WindSTAR-Pro, which is developed to handle the modeling of long distance acoustic propagation. As specific features of the WindSTAR-Pro package, the rotation of the noise sources is modeled, the propagation simulations combine the so-called Parabolic Equations (PE) propagation model with numerical flow simulations to take into account effects from wind turbine wakes, atmospheric turbulence and wind shear.

To upgrade pyrolysis vapors derived from the catalytic fast pyrolysis (CFP) of Baiyinhua lignite (BYHL) in a drop tube reactor, various Co-loading (1, 3, 6 and 10 wt%) zeolites were prepared via wet impregnation. The effect of Co-loading and pyrolysis temperature ranged from 400 to 700 °C on product yields and tar properties were investigated in this work. The results showed that the product yield and the composition of pyrolysis tar were significantly affected by Co-modified HZSM-5 and parent HZSM-5 compared with no catalyst. Incorporation of metal-Co in HZSM-5 had an additional effect on the performance of the parent HZSM-5. The total content of benzene (B), toluene (T), ethylbenzene (E), xylene (X) and naphthalene (N) significantly increased and it reached 24.2 mg/g at Co-loading of 3 wt% (3Co-H-5) at 600 °C. 3Co-H-5 exhibited also a promising performance in lowering the oxygen content from 49.8% without a catalyst to 14.6% by GC–MS analysis. The deoxygenation mechanisms over metal-Co active centers and acid-catalyzed reactions, such as isomerization and cracking, over acid sites of HZSM-5 were speculated in this work. In addition, the temperature of 600 °C is not only appropriate for fast pyrolysis of lignite to obtain a higher pyrolysis tar, but also for catalytic pyrolysis to obtain BTEXN.

The structural evolution of coal during pyrolysis process has been studied for a long time but remains unclear, mainly due to the extraordinary complexity of coal structure. The present study aimed to further identify the chemical structural evolution of different parts in the semi-chars obtained by low-temperature pyrolysis of a Chinese low-rank coal (Shenfu coal). Semi-chars and their solvent extracted materials (oil, resin, asphaltene and preasphaltene) were analyzed by 13C nuclear magnetic resonance (NMR) mass spectrometry, diffuse reflectance Fourier transform-infrared spectroscopy (DRIFTs) and ultraviolet (UV) fluorescence spectroscopy, separately. The results showed that 23.8% weight loss occurred during the whole pyrolysis process at 435 °C and half of the weight loss was achieved in the initial five minutes. By contrast, amount of the extracts in semi-chars (solvent extracted metaplast materials) decreased more dramatically in the initial stage of the pyrolysis, and 51.8% of the extracts disappeared in the initial one minute. Oil and preasphaltene showed higher thermal sensitivity than asphaltene and resin. Considerable content of metaplast materials with 1–2 rings (especially in oil and/or asphaltene) were produced along with the pyrolysis process. Condensed aromatic structures in semi-chars were relatively stable and mainly decomposed in the initial stage of pyrolysis which could be attributed to the dramatically decomposition of some active aromatic structures with ≥ 4 rings (especially the components in extracts such as preasphaltene). The results provided a new insight into the structural evolution of coal during low-temperature pyrolysis process, which specially considered the detailed information of the solvent extractable metaplast materials in semi-chars.

The unsteady nature of wind turbine noise is a major reason for annoyance. The variation of far-field sound pressure levels is not only caused by the continuous change in wind turbine noise source levels but also by the unsteady flow field and the ground characteristics between the turbine and receiver. To take these phenomena into account, a consistent numerical technique that models the sound propagation from the source to receiver is developed. Large eddy simulation with an actuator line technique is employed for the flow modelling and the corresponding flow fields are used to simulate sound generation and propagation. The local blade relative velocity, angle of attack, and turbulence characteristics are input to the sound generation model. Time-dependent blade locations and the velocity between the noise source and receiver are considered within a quasi-3D propagation model. Long-range noise propagation of a 5 MW wind turbine is investigated. Sound pressure level time series evaluated at the source time are studied for varying wind speeds, surface roughness, and ground impedances within a 2000 m radius from the turbine.

Most studies on offshore wind farm design assume a uniform wind farm, which consists of an identical type of wind turbines. In order to further reduce the cost of energy, we investigate the design of non-uniform offshore wind farms, i.e., wind farms with multiple types of wind turbines and hub-heights. Given a set of different types of wind turbines with a different default hub height for each type, we can specify the design of a wind farm by the types of turbines, number of turbines for each type, and turbine locations. We consider the optimization of such design to minimize the levelized cost of energy, which is calculated using a capital cost model that covers the turbine cost and the balance of plant cost. An empirical wind turbine design cost and scaling model is utilized to model the cost of turbines with different sizes. Constraints on wind farm boundary, wind turbine proximity and total capacity are also included. We solve the problem with a newly developed extended random search algorithm and tested it in a realistic design optimization problem based on the Horns Rev 1 offshore wind farm in Denmark. The optimized non-uniform designs are compared with their uniform counterparts. We find that a non-uniform design can achieve a lower levelized cost of energy than its uniform counterparts, when the capital cost per MW is slightly lower for the smaller size turbine. Comparison with the mixed-discrete particle swarm optimization algorithm is also carried out for a non-uniform wind farm design problem with a fixed number of turbines, which shows the effectiveness and superiority of the proposed algorithm. Finally, the advantages and possible disadvantages of non-uniform design are also identified and discussed.

In this paper, we investigate the sound propagation from a wind turbine considering the effects of wake-induced velocity deficit and turbulence. In order to address this issue, an advanced approach was developed in which both scalar and vector parabolic equations in two dimensions are solved. Flow field input was obtained using the actuator line (AL) technique with Large Eddy Simulation (LES) to model the wind turbine and its wake and from an analytical wake model. The effect of incoming wind speed and atmospheric stability was investigated with the analytical wake input using a single point source. Unsteady acoustic simulations were carried out with the AL/LES input for three cases with different incoming turbulence intensity, and a moving source approach to mimic the rotating turbine blades. The results show a non-negligible effect of the wake on far-field noise prediction. Particularly under stable atmospheric conditions, SPL amplification reaches up to 7.5 dB at the wake centre. Furthermore, it was observed that when the turbulence intensity level of the incoming flow is higher, the SPL difference between the moving and the steady source is lower.

The blade element momentum (BEM) theory is widely used in aerodynamic performance calculations and optimization applications for wind turbines. The fixed point iterative method is the most commonly utilized technique to solve the BEM equations. However, this method sometimes does not converge to the physical solution, especially for the locations near the blade tip and root where the failure rate of the iterative method is high. The stability and accuracy of aerodynamic calculations and optimizations are greatly reduced due to this problem. The intrinsic mechanisms leading to convergence problems are addressed through both theoretical analysis and numerical tests. A term from the BEM equations equals to zero at a critical inflow angle is the source of the convergence problems. When the initial inflow angle is set larger than the critical inflow angle and the relaxation methodology is adopted, the convergence ability of the iterative method will be greatly enhanced. Numerical tests have been performed under different combinations of local tip speed ratio, local solidity, local twist and airfoil aerodynamic data. Results show that the simple iterative methods have a good convergence ability which will improve the aerodynamic or structural design of wind turbines. Copyright © 2017 John Wiley & Sons, Ltd.

The improved analytical wake model named as 2D_k Jensen model (which was proposed to overcome some shortcomes in the classical Jensen wake model) is applied and validated in this work for wind turbine multi-wake predictions. Different from the original Jensen model, this newly developed 2D_k Jensen model uses a cosine shape instead of the top-hat shape for the velocity deficit in the wake, and the wake decay rate as a variable that is related to the ambient turbulence as well as the rotor generated turbulence. Coupled with four different multi-wake combination models, the 2D_k Jensen model is assessed through (1) simulating two wakes interaction under full wake and partial wake conditions and (2) predicting the power production in the Horns Rev wind farm for different wake sectors around two different wind directions. Through comparisons with field measurements, results from Large Eddy Simulations (LES) as well as results from other commercial codes, it is found that the predictions obtained with the 2D_k Jensen model exhibit good to excellent agreements with experimental and LES data.

The Actuator Disc/Navier-Stokes (AD/NS) method has played a significant role in wind farm simulations. It is based on the assumption that the flow is azimuthally uniform in the rotor plane, and thus, requires a tip loss correction to take into account the effect of a finite number of blades. All existing tip loss corrections were originally proposed for the Blade-Element Momentum Theory (BEMT), and their implementations have to be changed when transplanted into the AD/NS method. The special focus of the present study is to investigate the performance of tip loss corrections combined in the AD/NS method. The study is conducted by using an axisymmetric AD/NS solver to simulate the flow past the experimental NREL Phase Ⅵ wind turbine and the virtual NREL 5MW wind turbine. Three different implementations of the widely used Glauert tip loss function F are discussed and evaluated. In addition, a newly developed tip loss correction is applied and compared with the above implementations. For both the small and large rotors under investigation, the three different implementations show a certain degree of difference to each other, although the relative difference in blade loads is generally no more than 4%. Their performance is roughly consistent with the standard Glauert correction employed in the BEMT, but they all tend to make the blade tip loads over-predicted. As an alternative method, the new tip loss correction shows superior performance in various flow conditions. A further investigation into the flow around and behind the rotors indicates that tip loss correction has a significant influence on the velocity development in the wake.

The angle of attack (AoA) is the key parameter when extracting the aerodynamic polar from the rotating blade sections of a wind turbine. However, the determination of AoA is not straightforward using computational fluid dynamics (CFD) or measurement. Since the incoming streamlines are bent because of the complex inductions of the rotor, discrepancies exist between various existing determination methods, especially in the tip region. In the present study, flow characteristics in the region near wind turbine blades are analyzed in detail using CFD results of flows past the NREL UAE Phase VI rotor. It is found that the local flow determining AOA changes rapidly in the vicinity of the blade. Based on this finding, the concepts of effective AoA as well as nominal AoA are introduced, leading to a new method of AOA determination. The new method has 5 steps: (1) Find the distributed vortices on the blade surface; (2) select two monitoring points per cross-section close to the aerodynamic center on both pressure and suction sides with an equal distance from the rotor plane; (3) subtract the blade self-induction from the velocity at each monitoring point; (4) average the velocity of the two monitoring points obtained in Step 3; (5) determine the AoA using the velocity obtained in Step 4. Since the monitoring points for the first time can be set very close to the aerodynamic center, leading to an excellent estimation of AoA. The aerodynamic polar extracted through determination of the effective AoA exhibits a consistent regularity for both the mid-board and tip sections, which has never been obtained by the existing determination methods.

Blade element momentum (BEM) theory is widely used in aerodynamic performance predictions and design applications for wind turbines. However, the classic BEM method is not quite accurate which often tends to under-predict the aerodynamic forces near root and over-predict its performance near tip. The reliability of the aerodynamic calculations and design optimizations is greatly reduced due to this problem. To improve the momentum theory, in this paper the influence of pressure drop due to wake rotation and the effect of radial velocity at the rotor disc in the momentum theory are considered. Thus the axial induction factor in far downstream is not simply twice of the induction factor at disc. To calculate the performance of wind turbine rotors, the improved momentum theory is considered together with both Glauert’s tip correction and Shen’s tip correction. Numerical tests have been performed for the MEXICO rotor. Results show that the improved BEM theory gives a better prediction than the classic BEM method, especially in the blade tip region, when comparing to the MEXICO measurements.

A comparative analysis of the RANS-based generalized actuator disc method (AD/RANS) with different turbulence models for simulating single wind & tidal turbine wakes and double wake interactions is performed. The tested turbulence models include the Realizable k-e, SST k-ω, Linear Reynolds-stress (RSM) and two proposed RSM models with modified closure constants. The evaluation is based on comparing their results against five sets of published experimental data for various types of turbines operating under a wide range of inflow conditions. Special emphasis is put on both horizontal and vertical distributions of velocity deficit and turbulence intensity throughout the whole wake region. The results identify that the wake flow prediction is particularly sensitive to the turbulence model implemented, with a maximum difference reaching up to 40%. Overall, the proposed Mod2 RSM model (along with a new derivation of turbulence intensity) is recommended as a robust choice for capturing wake behaviors, in both near and far field from the turbine. Additionally, the weaknesses and strengths of other models are discussed, aiming to give a guideline for choosing the right model for the right job as well as to provide a reference study about the accuracy improvement of wake predictions.

The underground tunnel is of key importance to the ventilation in a pumped storage power station (PSPS). The heat and moisture environment of PSPS directly affects the operation safety of electrical equipment and the health of workers. The present work aims to analyze the influence of industrial dehumidifiers in the traffic tunnel on the ventilation performance. A field test in a PSPS was carried out, and the results showed that the temperature of the overall traffic tunnel decreases no longer in an exponential mode as compared with that without industrial dehumidifiers. A new model to predict the temperature decrease is proposed for tunnels, and the results of the new model are in good agreement with the test results. The industrial dehumidifiers can control the relative humidity to meet the requirements, and the average outlet temperature is found 3.85 °C higher than the historical data. The higher entrance temperature gives the higher stable value of cooling efficiency at the outlet of traffic tunnel, and the higher relative humidity of the entrance gives the higher relative humidity of the outlet. Under the similar entrance temperature in the traffic tunnel, the dehumidification efficiency reaches approximate value at the outlet. Meanwhile, dehumidification efficiency can be enhanced by an average of 7%–9% with TC increased 2 °C.

Layout optimization of wind farms constitutes an important and challenging task in complex terrain. This is especially due to the complex interactions of the boundary layer flows in complex terrain and wind turbine wakes, which renders wake modelling in complex terrain difficult. This study tackles this challenge with a new engineering wake model, which is developed by superposing a Gaussian shape wake model on top of the background flow field, assuming that the centerlines of wind turbine wakes follow the streamlines of the background flow field. The model is found to predict wind turbine wakes in complex terrain with good accuracy and at the same time it is computationally cheap to run for optimization applications. Comparisons with high fidelity simulations and field measurements for a real wind farm with 25 turbines in complex terrain demonstrate its effectiveness. A systematic comparison of eight optimization algorithms, which includes two gradient-based and six gradient-free algorithms, is also carried out for the layout optimization problem in complex terrain. To accelerate the optimization process, a double-stage approach is proposed, which optimizes the objective function first neglecting wake effects and then, in the second stage, including them. While all the tested optimization algorithms can improve the original wind farm layout, random search, local search, and pattern search are found to be the top three algorithms in terms of optimization results and computational cost.

Designing wind farms in complex terrain is an important task, especially for countries with a large portion of complex terrain territory. To tackle this task, an optimization framework is developed in this study, which combines the solution from a wind resource assessment tool, an engineering wake model adapted for complex terrain, and an advanced wind farm layout optimization algorithm. Various realistic constraints are modelled and considered, such as the inclusive and exclusive boundaries, minimal distances between turbines, and specific requirements on wind resource and terrain conditions. The default objective function in this framework is the total net annual energy production (AEP) of the wind farm, and the Random Search algorithm is employed to solve the optimization problem. A new algorithm called Heuristic Fill is also developed in this study to find good initial layouts for optimizing wind farms in complex terrain. The ability of the framework is demonstrated in a case study based on a real wind farm with 25 turbines in complex terrain. Results show that the framework can find a better design, with 2.70% higher net AEP than the original design, while keeping the occupied area and minimal distance between turbines at the same level. Comparison with two popular algorithms (Particle Swarm Optimization and Genetic Algorithm) also shows the superiority of the Random Search algorithm.

This paper focuses on the efficiency improvement of a centrifugal fan used in a vacuum cleaner. In order to check the performance of the centrifugal fan system, computational fluid dynamics (CFD) analysis is used. The numerical simulation with CFD tool is carried out with RNG [Formula: see text] two-equation turbulence model based on Reynolds-averaged Navier–Stokes equations. To perform the coupling between rotating impeller and stationary area, the multiple reference frame (MRF) model is used. The numerical results of the fan are validated against with experimental results and are found to be highly reliable. The design and optimization of diffuser and impeller of a centrifugal fan are realized by using numerical investigations. For reducing the kinetic energy loss inside the fan, a guide baffle is added to optimize diffuser. The optimization results show that overall efficiency of the fan is improved by 5.27% and considering the lower efficiency of impeller caused by blockage at the blade inlet, etc., the design of impeller with long-short blades is proposed. Several cases of affecting factors under different operating conditions are simulated. Relative length (denoted as [Formula: see text]) and circumferential position of short blades are chosen as design variables. It is found that the efficiency of a fan with a relative length of 0.7 can be increased by 9.34%, and the best circumferential position of short blades is between two adjacent long blades.

As part of the AVATAR and Mexnext projects, this study compares several methods used to derive lifting line variables from CFD simulations of the MEXICO rotor in yawed inflow. The results from six partners within the AVATAR/Mexnext consortium using five different methods of extraction were compared. Overall comparison of the induced velocities at the mid and tip parts of blade shows fairly good agreement between the tested methods, where the derived angle of attack differs within 1°, within the linear range this accounts to ˂ 10% uncertainty on the aerodynamic forces. The presented comparison shows inadequate agreement between the methods for application towards the root., peer-reviewed

This paper presents a new variable pitch (VP) approach to increase the peak power coefficient of the straight-bladed vertical-axis wind turbine (VAWT), by widening the azimuthal angle band of the blade with the highest aerodynamic torque, instead of increasing the highest torque. The new VP-approach provides a curve of pitch angle designed for the blade operating at the rated tip speed ratio (TSR) corresponding to the peak power coefficient of the fixed pitch (FP)-VAWT. The effects of the new approach are exploited by using the double multiple stream tubes (DMST) model and Prandtl&rsquo, s mathematics to evaluate the blade tip loss. The research describes the effects from six aspects, including the lift, drag, angle of attack (AoA), resultant velocity, torque, and power output, through a comparison between VP-VAWTs and FP-VAWTs working at four TSRs: 4, 4.5, 5, and 5.5. Compared with the FP-blade, the VP-blade has a wider azimuthal zone with the maximum AoA, lift, drag, and torque in the upwind half-cycle, and yields the two new larger maximum values in the downwind half-cycle. The power distribution in the swept area of the turbine changes from an arched shape of the FP-VAWT into the rectangular shape of the VP-VAWT. The new VP-approach markedly widens the highest-performance zone of the blade in a revolution, and ultimately achieves an 18.9% growth of the peak power coefficient of the VAWT at the optimum TSR. Besides achieving this growth, the new pitching method will enhance the performance at TSRs that are higher than current optimal values, and an increase of torque is also generated.

In the present study, a computational fluid dynamic (CFD)-based blade optimization algorithm is introduced for designing single or multiple wind turbine rotors. It is shown that the CFD methods provide more detailed aerodynamics features during the design process. Because high computational cost limits the conventional CFD applications in particular for rotor optimization purposes, in the current paper, a CFD-based 2D Actuator Disc (AD) model is used to represent turbulent flows over wind turbine rotors. With the ideal case of axisymmetric flows, the simulation time is significantly reduced with the 2D method. The design variables are the shape parameters comprising the chord, twist, and relative thickness of the wind turbine rotor blades as well as the rotational speed. Due to the wake effects, the optimized blade shapes are different for the upstream and downstream turbines. The comparative aerodynamic performance is analyzed between the original and optimized reference wind turbine rotor. The results show that the present numerical optimization algorithm for multiple turbines is efficient and more advanced than conventional methods. The current method achieves the same accuracy as 3D CFD simulations, and the computational efficiency is not significantly higher than the Blade Element Momentum (BEM) theory. The paper shows that CFD for rotor design is possible using a high-performance single personal computer with multiple cores.

In order to investigate the unsteady performance of blunt wind turbine airfoils caused by boundary layer separation and wake eddies, this paper studies the aerodynamic performance by large eddy simulation (LES) and wind tunnel experiment at a Reynolds number of 2.62 × 10ˆ5. The blunt airfoils are obtained by enlarging the trailing edge of the DU 91-W2-250 airfoil to 6% and 10% chords symmetrically on both pressure and suction sides of the airfoil. The simulation was carried out with the incompressible finite-volume Navier-Stokes code EllipSys3D; and, the experiment was done in a wind tunnel with a cross-section of 0.5 m × 0.5 m by measuring the surface pressure and wake velocities using ESP-64HD pressure scanner and TSI hot-wire anemometer. The unsteady wake was captured by hot-wire in the wind tunnel, and LES with EllipSys3D. Both experiment and LES show that the spectrum of aerodynamic forces has a broadband nature which is in coincidence with the wake eddies, implying that the unsteady Karman vortex sheet is the driving mechanism of the force fluctuation. Moreover, the trailing edge size affects the separation bubbles and transition process in the boundary layer. It shows that the boundary layer near the leading edge is unstable in the spanwise direction, which is characterized by low frequency waves.

The propagation of aerodynamic noise from multi-wind turbines is studied. An efficient hybrid method is developed to jointly predict the aerodynamic and aeroacoustics performances of wind turbines, such as blade loading, rotor power, rotor aerodynamic noise sources, and propagation of noise. This numerical method combined the simulations of wind turbine flow, noise source and its propagation which is solved for long propagation path and under complex flow environment. The results from computational fluid dynamics (CFD) calculations not only provide wind turbine power and thrust information, but also provide detailed wake flow. The wake flow is computed with a 2D actuator disc (AD) method that is based on the axisymmetric flow assumption. The relative inflow velocity and angle of attack (AOA) of each blade element form input data to the noise source model. The noise source is also the initial condition for the wave equation that solves long distance noise propagation in frequency domain. Simulations were conducted under different atmospheric conditions which showed that wake flow is an important part that has to be included in wind turbine noise propagation.

The current article describes the conceptual design of a rotor for a 5 MW machine situated at an offshore site in China (OffWindChina). The OffWindChina 5 MW rotor design work was divided into two parts between the Technical University of Denmark (DTU) and the Chong Qing University (CQU). The two parts consist of the aeroelastic and structural design phases. The aeroelastic part determines the optimal outer blade shape in terms of cost of energy (COE), while the structural part determines the internal laminate layup to achieve a minimum blade mass. Each part is performed sequentially using in-house optimization tools developed at DTU and CQU. The designed blade yields a high energy output while maintaining the structural feasibility with respect to international standards.

To enhance the performance of horizontal axis wind turbines, it is proposed to place a cylindrical disc in front of the rotor in order to lead the incoming flow from the inner part to the outer part of the rotor blades. This is expected to increase the power output, as the kinetic energy is mainly captured at the outer part of the blades, where the relative wind speed is high. To assess the impact of this novel design idea, a hybrid numerical technique, based on solving the Reynolds-averaged Navier-Stokes equations, is utilized to determine the aerodynamic performance. The in-house developed EllipSys3D code, which is employed as basic numerical solver, is combined with an actuator disc representation of the wind turbine rotor and an immersed boundary technique for representing the upstream cylindrical disc. The impact of the disc on the rotor performance is assessed by systematically changing the size of the circular disc and its axial distance to the rotor. Based on a numerical study of a Megawatt size commercial wind turbine, it is found that up to 1.5% additional energy can be captured by placing a circular disc with a suitable diameter upstream of the rotor plane.

Wind farms operate often in the changing wind. The wind condition variations in a wide range of time scales lead to the variability of wind farms’ power production. This imposes a major challenge to the power system operators who are facing a higher and higher penetration level of wind power. Thus, wind farm developers/owners need to take the variability into consideration in the designing/planning stage, in addition to the conventional main objective of maximizing the expected power output under a fixed wind distribution. In this study, we first propose a new metric to evaluate the variability of wind power based on the characteristics of the wind farm and its local wind conditions. Then a series of robustness metrics are proposed to quantify wind farm’s ability to produce power with high mean value and low variability under changing wind, considering both short-term and long-term wind condition variations. Based on these metrics, wind farm layout optimization is performed to maximize the robustness of a real offshore wind farm in Denmark. The results demonstrate that the robustness metrics are more flexible and complete than the conventional metrics for characterizing wind farm power production, such as mean power output or wind power variability alone, and it is feasible to design wind farms to produce power with high mean value and low variability.

Variable-pitch (VP) technology is an effective approach to upgrade the aerodynamics of the blade of an H-type vertical-axis wind turbine (VAWT). At present, most of the research efforts are focused on the performance improvement of the azimuth angle owing to the large angle of attack (AoA). On the blade circular path of an H-type VAWT, there are two azimuth positions where torques are negative, and the performance is the poorest. The vicinity zones of the two azimuths also have low performance and greatly weaken the overall productivity of VAWT. In this paper, we propose a new technology that, unlike the traditional VP-technology, focuses mainly on the aerodynamics improvement of the azimuth position with small AoA. The purpose of this novel approach is to widen the band of azimuth positions with high performance and eventually enhance the power efficiency of the overall VAWT. The performance of the new VP-VAWT is predicted using the Double Multiple Streamtubes model and Prandtl's mathematics to evaluate the blade tip loss. Compared with the fixed-pitch (FP) blade, the VP-blade has a wider zone of the max AoA and tangential force in the upwind half-circle and yields the two new larger max values in the downwind half-circle. The new VP-strategy considerably narrows the two low-torque zones near the 0° and 180° azimuths and markedly widens the high-torque azimuth zone; the torque distribution appears in a trapezoidal shape in the upwind region and an M-like shape in the downwind region. The power distribution in the swept area of turbine changes from an arched shape of the FP-VAWT into a rectangular shape of the VP-VAWT. At last, an 18.9% growth in power efficiency is achieved. All of the above results confirm that the new VP-technology can effectively improve VAWT performance and also widens the highest performance tip speed ratio zone which makes the turbines capable of running with high efficiency in wider zones.

Vortex generators (VGs) are commonly placed on wind turbine blades to delay flow separation in the boundary layer. VGs can be parametrically modeled in computational fluid dynamics for effective and efficient simulations of wind blade flow fields. Many researchers have studied the vortex circulation created by VGs and created various parametric models used with the Navier-Stokes equations, but most of them are based on a single winglet of VGs and do not include the inter-effects between the winglets. This paper proposes a parameterized VG array model based on counter-rotating VGs, which properly takes into account the inter-effects between winglets. Two cases, i.e., a plate with a pair of VGs and a DU-W2-250 blade segment with five pairs of VGs, are investigated to validate this model; the array type parametric model is in closer agreement with experimental data than traditional models. Compared to the solid VG model, the array type model has similar streamlines and surface pressure coefficients on the suction surface. The array type VG model can effectively reduce the number of grid points and yield highly accurate predictions of wind turbine blade aerodynamic characteristics.

Aerodynamic and structural dynamic performance analysis of modern wind turbines are routinely estimated in the wind energy field using computational tools known as aeroelastic codes. Most aeroelastic codes use the blade element momentum (BEM) technique to model the rotor aerodynamics and a modal, multi-body or the finite-element approach to model the turbine structural dynamics. The present work describes the development of a novel aeroelastic code that combines a three-dimensional viscous–inviscid interactive method, method for interactive rotor aerodynamic simulations (MIRAS), with the structural dynamics model used in the aeroelastic code FLEX5. The new code, called MIRAS-FLEX, is an improvement on standard aeroelastic codes because it uses a more advanced aerodynamic model than BEM. With the new aeroelastic code, more physical aerodynamic predictions than BEM can be obtained as BEM uses empirical relations, such as tip loss corrections, to determine the flow around a rotor. Although more costly than BEM, a small cluster is sufficient to run MIRAS-FLEX in a fast and easy way. MIRAS-FLEX is compared against the widely used FLEX5 and FAST, as well as the participant codes from the Offshore Code Comparison Collaboration Project. Simulation tests consist of steady wind inflow conditions with different combinations of yaw error, wind shear, tower shadow and turbine-elastic modeling. Turbulent inflow created by using a Mann box is also considered. MIRAS-FLEX results, such as blade tip deflections and root-bending moments, are generally in good agreement with the other codes. Copyright © 2017 John Wiley & Sons, Ltd.

The authors would like to thank Niels N. Sørensen from DTU for providing the CFD simulations. This project has received partly funding from the European Union 7th framework program for research, technological development and demonstration under the grant agreement No FP7- ENERGY-2013-1/no 608396 (AVATAR project). This work has also partly supported by the Energy Technology Development and Demonstration Program (EUDP-2014, J. nr. 64014-0543) under the Danish Energy Agency., This work presents an investigation on different methods for the calculation of the angle of attack and the underlying induced velocity on wind turbine blades using data obtained from three dimensional computational fluid dynamics. Several methods were examined and their advantages as well as shortcomings were presented. The investigations were performed for flows past two 10MW reference wind turbines under axial inflow conditions, namely the 10MW turbines designed in the EU AVATAR and INNWIND.EU projects. The results shown that the evaluated methods are in good agreement with each other at the mid-span, though some deviations were observed at the root and tip regions of the blades. Using any of the proposed methods, it is possible to obtain airfoil characteristics for lift and drag coefficients as a function of the angle of attack. Furthermore, by using the extracted data new correction models can be derived for blade element momentum calculations., non peer-reviewed

Experimental data acquired in the New MEXICO experiment on a yawed 4.5m diameter rotor model turbine are used here to validate the actuator line (AL) and actuator disc (AD) models implemented in the Large Eddy Simulation code EllipSys3D in terms of loadingand velocity field. Even without modelling the geometry of the hub and nacelle, the AL and AD models produce similar results that are generally in good agreement with the experimental data under the various configurations considered. As expected, the AL model does better at capturing the induction effects from the individual blade tip vortices, while the AD model can reproduce the averaged features of the flow. The importance of using high quality airfoil data (including 3D corrections) as well as a fine grid resolution is highlighted by the results obtained. Overall, it is found that both models can satisfactorily predict the 3D velocity field and blade loading of the New MEXICO rotor under yawed inflow. This work was also supported by the Energy Technology Development and Demonstration Program (EUDP2014, J. nr. 64014-0543) under the Danish Energy Agency.

In this paper, a computational model for predicting the aerodynamic behavior of wind turbine wakes and blades subjected to unsteady motions and viscous effects is presented. The model is based on a three-dimensional panel method using a surface distribution of quadrilateral sources and doublets, which is coupled to a viscous boundary layer solver. Unlike Navier-Stokes codes that need to solve the entire flow domain, the panel method solves the flow around a complex geometry by distributing singularity elements on the body surface, obtaining a faster solution and making this type of codes suitable for the design of wind turbines. A free-wake model has been employed to simulate the wake behind a wind turbine by using vortex filaments that carry the vorticity shed by the trailing edge of the blades. Viscous and rotational effects inside the boundary layer are taken into account via the transpiration velocity concept, applied using strip theory with the cross sectional angle of attack as coupling parameter. The transpiration velocity is obtained from the solution of the integral boundary layer equations with extension for rotational effects. It is found that viscosity plays a very important role in the predictions of blade aerodynamics and wake dynamics, especially at high angles of attack just before and after boundary layer separation takes place. The present code is validated in detail against the well-known MEXICO experiment and a set of non-rotating cases. Copyright © 2014 John Wiley & Sons, Ltd.

Monin&ndash, Obukhov similarity theory (MOST) overestimates the mean vertical velocity gradient in some atmospheric stable conditions, i.e., Richardson number R f &lt, 0 . 25 . To obtain a given hub-height inflow velocity for a certain roughness length, this overestimated velocity gradient underpredicts the friction wind speed and the turbulence intensity, potentially influencing wake modeling of a wind turbine. This work investigates the side effects of the breakdown of MOST on wake modeling under stable conditions and makes some modifications to the flow similarity functions to eliminate these side effects. Based on a field measurement in a wind farm, we first show that MOST predicts a larger velocity gradient for the atmospheric stability parameter &zeta, &gt, 0 . 1 and proposes new flow similarity functions without constraining R f to limit the overestimated velocity gradient. Next, different turbulence models based on MOST and a modified one based on the new similarity functions are investigated through numerical simulations. These turbulence models are combined with the actuator disk model (AD) and Reynolds-averaged Navier&ndash, Stokes equations (RANS) to model wind turbine wakes under stable conditions. As compared to measurements, numerical results show that turbulence models based on MOST result in a larger wake deficit and a slower wake recovery rate with a root-mean-squared error (RSME) of wake deficit in the range of 0.07 to 0.20. This overestimated wake effect is improved by applying the new similarity functions, and the RSME of wake deficit is reduced by 0.05 on average.

In this article, airfoil trailing edge bluntness noise is investigated using both computational aero-acoustic and semi-empirical approach. For engineering purposes, one of the most commonly used prediction tools for trailing edge noise are based on semi-empirical approaches, for example, the Brooks, Pope, and Marcolini airfoil noise prediction model developed by Brooks, Pope, and Marcolini (NASA Reference Publication 1218, 1989). It was found in previous study that the Brooks, Pope, and Marcolini model tends to over-predict noise at high frequencies. Furthermore, it was observed that this was caused by a lack in the model to predict accurately noise from blunt trailing edges. For more physical understanding of bluntness noise generation, in this study, we also use an advanced in-house developed high-order computational aero-acoustic technique to investigate the details associated with trailing edge bluntness noise. The results from the numerical model form the basis for an improved Brooks, Pope, and Marcolini trailing edge bluntness noise model.

Despite the advances in computing resources in the recent years, the majority oflarge wind-turbine rotor design problems still rely on aero-elastic codes that use blade element momentum (BEM) approaches to model the rotor aerodynamics. The present work describes an approach to wind-turbine rotor design by incorporating a higher- delity free-wake panel aero-elastic coupling code called MIRAS-FLEX. The optimization procedure includes a series of design load cases and a simple structural design code. Due to the heavy MIRAS-FLEX computations, a surrogate-modeling approach is applied to mitigate the overall computational cost of the optimization. Improvements in cost of energy, annual energy production, maximum ap-wise root bending moment, and blade mass were obtained for the NREL 5MW baseline wind turbine.

Actuator line and disc techniques are employed to analyse the wake obtained in the New MEXICO wind turbine experiment. The New MEXICO measurement campaign done in 2014 is a follow-up to the MEXICO campaign, which was completed in 2006. Three flow configurations in axial flow condition are simulated and both computed loads and velocity fields around the rotor are compared with detailed PIV measurements. The comparisons show that the computed loadings are generally in agreement with the measurements under the rotor's design condition. Both actuator approaches under-predicted the loading in the inboard part of blade in stall condition as only 2D airfoil data were used in the simulations. The predicted wake velocities generally agree well with the PIV measurements. In the experiment, PIV measurements are also provided close to the hub and nacelle. To study the effect of hub and nacelle, numerical simulations are performed both in the presence and absence of the hub geometry. This study shows that the large hub used in the experiment has only small effects on overall wake behaviour.