bluuebunny/crossref_metadata_2025 huggingface dataset:
Aero-structural Design of Composite Wings for Airborne Wind Energy Applications
Authors: Candade Ashwin A. , Ranneberg Maximillian , Schmehl Roland
Published: September 2020

In this work we explore the initial design space for composite kites, focusing on the configuration of the bridle line system and its effect on the aeroelastic behaviour of the wing. The computational model utilises a 2D cross sectional model in conjunction with a 1D beam model (2+1D structural model) that captures the complex composite coupling effects exhibited by slender, multi-layered composite structures, while still being computationally efficient for the use at the initial iterative design stage. This structural model is coupled with a non-linear vortex lattice method (VLM) to determine the aerodynamic loading on the wing. In conjunction with the aerodynamic model, a bridle model is utilised to determine the force transfer path between the wing and the bridles connected with the tethers leading to the ground station. The structural model is coupled to the aerodynamic and bridle models in order to obtain the equilibrium aero-structural-bridle state of the kite. This computational model is utilised to perform a design space exploration to assess the effects of varied load introduction to the structure and resulting effects on the kite.
Simulative investigation of the load propagation in a wind turbine drive train during a power converter fault
Authors: Röder Julian , Jacobs Georg , Duda Tobias , Bosse Dennis
Published: September 2020

Highly dynamic load situations in the drive train of wind turbines can occur during operation as a result of faults in the electrical grid or damage in electrical components. The dynamic loads can lead to damage or increased wear in the drive train components. At the Center for Wind Power Drives a wind turbine research nacelle has been set up in the course of a national project. Extensive experiments with this research nacelle have been conducted with the corresponding 4 MW test rig. Furthermore multi body simulation (MBS) models of the nacelle and the test rig have been developed and validated by experiments with load cases defined in the IEC 61400. Among other experiments, a test with a highly dynamic load situation in case of a power converter fault has been conducted. For that particular load case a power converter short-circuit has been emulated. This test’s results show significant high torque reversals inside the drivetrain. This paper focuses on the implementation of the measured dynamic torque excitation in the existing MBS model in order to investigate the calculated torque load propagation from the high speed side to the low speed side of the drive train. The MBS model delivers further insight into the torque load propagation by providing the torque on the intermediate speed shaft (IMS) which could not be measured on the test bench. It is shown that the highly dynamic torque ripple is filtered out mainly in the spur gear stage from the HSS to the IMS.
Why is the measured maximum lift in wind tunnels dependent on the measurement method?
Authors: Olsen A S , Sørensen N N , Bak C , Gaunaa M , Mikkelsen R , Fischer A , Beckerlee J , Ildvedsen S
Published: September 2020

The present study investigates the differences in the predicted lift for a wind tunnel model from either surface pressures or side wall pressures. The investigated model is the NACA63-418 tested in the Poul la Cour tunnel. The measurements are compared with previous conducted wind tunnel campaigns for a Reynolds number of 3E6. The 3D CFD model of the wind tunnel will be used for investigating details of the flow mechanisms, and to validate assumptions and findings from the experimental data. The CFD simulations show that when the flow is attached the lift based on the side wall pressures results in almost the same lift as calculated from the surface pressures. Around the maximum lift and in the stalled region the flow is not anymore 2D. For the NACA63-418 airfoil the lift based on the side wall pressures are generally highest. The CFD simulations confirm that the method used to predict the lift from the limited side wall pressure strips in the wind tunnel is applicable.
Implementation and Experimental Validation of a Dynamic Model of a 10 MW Nacelle Test Bench Load Application System
Authors: Siddiqui Muhammad Omer , Eich Norbert , Eustorgi Karin , Feja Paul
Published: September 2020

The 10 MW Dynamic Nacelle Testing Laboratory of Fraunhofer IWES provides a controlled environment for performing electrical and mechanical tests on a wind turbine nacelle. Apart from physical testing, system level simulations are another paradigm in the framework of nacelle testing. In this contribution, the development of a dynamic model of the load application system for the 10 MW nacelle test bench is presented. The test bench load application system controls are integrated in the model via co-simulation in Simulink. The model is evaluated using experimental results. By utilizing the modal strain recovery method, a direct comparison of the strain results of the model with the experimental results is achieved. Moreover, it is shown that the actual applied loads on the device under test can be estimated by analysing the strain readings. The developed model provides a platform for developing a high fidelity virtual nacelle test bench.
How much flow information can a turbine-mounted lidar capture?
Authors: Sekar Anantha Padmanabhan Kidambi , Rott Andreas , van Dooren Marijn Floris , Kühn Martin
Published: September 2020

Turbine-integrated lidar systems are capable of scanning the wind fields upstream of the turbine, opening up an opportunity to incorporate these measurements into the turbine itself. However, lidar measurements are always subject to uncertainties which are a result of the operating principle of the lidar. In this paper, we investigate and quantify the uncertainties associated with a turbine mounted “SpinnerLidar” in a high fidelity simulation framework. A sensitivity study is performed in order to investigate the effects of the spatio-temporal resolution, probe volume averaging and directional bias and recommendations are given for different lidar applications, e.g. turbulence research, load verification and control. It is seen that the SpinnerLidar in its current state is sufficient as a control input and for load verification studies especially capturing the rotational wind spectra very well. For estimating turbulence, it is better to operate the lidar at a much faster temporal sampling rate.
Impact of relative spacing of two adjacent vertical axis wind turbines on their aerodynamics
Authors: Sahebzadeh Sadra , Rezaeiha Abdolrahim , Montazeri Hamid
Published: September 2020

The impact of relative spacing on the individual and overall performance of two adjacent co-rotating Darrieus H-type VAWTs is investigated through high-fidelity URANS simulations, validated with experimental data. The simulations cover relative distances of 1.25d ≤ R ≤ 10d (d: turbine diameter) and relative angles of 0° ≤ Φ ≤ 90°. The relative angles of 30° ≤ Φ ≤ 75 with relative distance range of 1.25d ≤ R ≤ 5d are identified as the optimal regime with the highest overall power performance for the array. In this regime, the downstream turbine has a maximum increase of 5.1% in CP (R = 1.5d and Φ = 45°) with respect to an isolated solo rotor with similar characteristics. Local flow characteristics including wake length, wake expansion, vorticity and velocity fields are also investigated. It is found that for azimuthal angles of 90° ≤ θ ≤ 160° in the optimal regime, regions of accelerated flow are created due to the contraction of the flow between the turbines which benefit the downstream turbine CP and thus the overall power performance of the array. This provides an opportunity for a compact placement of turbines within a vertical-axis wind turbine farm and consequently increasing the farm power density.
Aerodynamic performance and blockage investigation of a cambered multi-bladed windmill
Authors: John Itoje H , Vaz Jerson R P , Wood David
Published: September 2020

Windmills for water pumping typically operate at low speed and high torque owing to their multi-bladed nature. This, however, complicates the rotor aerodynamic behavior due to the mutual interaction between adjacent blades and low Reynolds number, Re, operation. While studies on their aerodynamic performance indicate that increasing blade number, N, and airfoil type are critical analysis and design parameters, its low Re behavior with cambered airfoils appears complicated and is still poorly understood. Accordingly, the performance of a windmill model of diameter 0.68 m with 3 ≤ N ≤ 24 identical blades was investigated in two open jet wind tunnels, with different test section sizes: one with high blockage of 36.3 % and the other with a negligible blockage of 4.5 %, for comparison with Blade Element Theory (BET) predictions of thrust, torque, and power. It was found that BET is accurate except at low tip speed ratios, λ where it under-predicts the torque primarily because of the high solidity at high N. Furthermore, the study reveals that high blockage impacts significantly on rotor performance and is a function of N. Overall, the experiment gave a better performance, highlighting the importance of accounting for solidity in aerodynamic performance prediction.
Assessment of sensitivity and accuracy of BEM-based aeroelastic models on wind turbine load predictions
Authors: Caboni M. , Carrion M. , Rodriguez C. , Schepers G. , Boorsma K. , Sanderse B.
Published: September 2020

The general goal of the work reported in this paper is to gain more confidence when performing blade element momentum (BEM)-based aeroelastic simulations, especially when setting-up sub-models and their parameters. Due to limited or no information, the set-up of these methods is often highly uncertain. To achieve this objective, we have developed and used methodologies to perform the analysis of model uncertainty in wind turbine aeroelastic simulations, while assessing their accuracy. This paper presents an example where these methodologies have been applied to a) the different aerodynamic models used in BEM-based aeroelastic tools to account for unsteady airfoil aerodynamics (UAA) and b) key parameters used in one of these models (Beddoes-Leishman). The accuracy of the simulations is assessed by comparing the simulated unsteady loads with measurements from the DAN-AERO MW experiments. One of the main achievements of this work is the ability to assess the uncertainty in load predictions that derives from the uncertainty related to the UAA models and their constants. The study on the sensitivity of the parameters was performed using Sobol indices and showed that for the case under study the normal force standard deviation at outboard blade locations is mostly sensitive to the Beddoes-Leishman model’s vortex shedding time constant.
Simplified design criteria for drivetrains in direct-drive wind turbines
Authors: Lüdecke F D , Cheng P W
Published: September 2020

Nominal power of wind turbines constantly increases. This goes along with an increase of the generator size, usually accompanied with an increase in mass. To limit at the same time the tower top mass, the mass increase of the generator needs to be restricted. Changing the design concept of the generator to reduce mass, influences its modal behavior and thereby possibly the dynamics of the whole drivetrain. This work identifies simplified criteria for the parameter space restrictions of drivetrain designs, while taking into account the interaction of the generator electromagnetic and structural characteristics. The drivetrain is analysed as an integrated system using a simplified two mass model to evaluate the dependency of system parameters and system stability. For two degrees of freedom an analytical solution is determined. Increasing the number of degrees of freedom to four, the parameter study is carried out using a full factorial analysis and a numerical solution approach. The results point out the necessity to take into account magnetic stiffness when designing the drivetrain to ensure system stability.
Piecewise linear aeroelastic rotor-tower models for efficient wind turbine simulations
Authors: Macquart T , Scott S , Weaver P M , Pirrera A
Published: September 2020

The development of software and methodologies able to efficiently and accurately predict the aeroelastic performance of wind turbines at low computational cost — enabling the rapid turnaround of novel concepts — is key to further reducing the levelised cost of energy. However, even the conventional low fidelity methods used for preliminary blade and rotor design are computationally expensive. The authors propose to improve the computational efficiency of dynamic aeroelastic time domain simulations by substituting conventional models with a piecewise linear aeroelastic rotor-tower model. This novel piecewise linear model is described and compared against standard modelling tools in this paper. Results suggest that piecewise linear rotor-tower models can be used to accurately capture the aeroelastic dynamic of wind turbine blades, with a significant (5 – 20×) reduction in computational costs.
Feasibility study for the use of hydrodynamic plain bearings with balancing support characteristics as main bearing in wind turbines
Authors: Rolink Amadeus , Schröder Tim , Jacobs Georg , Bosse Dennis , Hölzl Johannes , Bergmann Philipp
Published: September 2020

The failure of a wind turbine’s main bearing leads to high maintenance costs which affects the economic competitiveness of wind energy as renewable energy source. Therefore, research is conducted to replace today’s used roller bearings by plain bearings. These can be designed segmented so that in case of a failure the segments can easily be exchanged on tower. As part of a former research project a 1 MW plain bearing with conical sliding surfaces was developed and tested on a full-scale system test bench. This contribution presents a methodology how this concept can be developed further and optimized to design a bearing in 3-point suspension or a moment bearing for high power classes.
Leading edge erosion of wind turbine blades: Effects of blade surface curvature on rain droplet impingement kinematics
Authors: Verma Amrit S. , Castro Saullo G.P. , Jiang Zhiyu , Hu Weifei , Teuwen Julie J.E.
Published: September 2020

The issue of leading edge erosion (LEE) of wind turbine blades (WTBs) is a complex problem that reduces the aerodynamic efficiency of blades, and affects the overall cost of energy. Several research efforts are being made at the moment to counter erosion of WTBs such as-testing of advanced coating materials together with development of high-fidelity computational models. However, the majority of these studies assume the coated surfaces as flat, while the surface curvature and the shape of the aerofoil at the blade’s leading-edge exposed to such rain fields is neglected. The present study questions the assumption of a flat surface, in the context of LEE of WTBs, and provides guidelines for erosion modelling. The critical parameters associated with rain droplet impingement kinematics on leading edge are compared for blade impact with (a) flat surface assumptions together with (b) the effects of the blade’s surface curvature. A parametric study is performed which includes WTBs of varying sizes and power ratings ranging from 750 KW to 10 MW, different positions along the blade length, and different rain droplet radii ranging from 0.1 mm to 5 mm for a land based wind turbine operating at rated wind speed. It is found in the study that droplet impingement kinematics are influenced by the surface curvature at the leading edge, the effect of which is significant for representing erosion at the blade tip for smaller blades, and for exposure to rainfall intensity with larger rain droplet size. A master curve describing the threshold level along the blade length is established for various WTBs and rainfall conditions, where flat surface approximation of the surface yields noticeable error and violates the impingement process. The results of the study are expected to aid the modeller in developing advanced numerical models for LEE for WTBs.
On Down-Scaled Modelling of Wind Turbine Drivetrains
Authors: Rebouças Geraldo F. de S. , Nejad Amir R.
Published: September 2020

Gearbox testing is an important and complex task that will become even more challenging as the wind industry moves towards ever-growing turbines. The burden of this task can be decreased by using reduced-scale models with similar characteristics as its industrial-scale equivalent. This work presents a step-by-step procedure to down-scale a gearbox to different fractions of its rated power while preserving its core properties: structural safety and frequency distribution. The parameters to be scaled are sub-divided according to their relation to the system’s integrity and dynamic behavior. After performing an overall scaling, it is possible to fine-tune the scaling factors, according to the user precision requirements. Simulations show that it is possible to down-scale a gearbox to 0.01 % of its rated power while having less than 10 % relative deviation on its pitting safety factor. These preliminary results show that wind turbine drivetrain testing can become more affordable by using down-scaled models in a structured manner.
Design of direct-drive wind turbine electrical generator structures using topology optimization techniques
Authors: Jaen-Sola P , Donald A S Mc , Oterkus E
Published: September 2020

Reducing the structural mass of low speed multi-MW electrical machines for renewable energy purposes have become an important object of study as with the drop in mass a substantial decrease in the machine capital cost can be achieved. Direct-drive wind turbine electrical generators need very robust and heavy supporting structures able to cope with the demanding requirements imposed by the environment and the forces and moments transmitted by the wind turbine rotor in order to maintain the air-gap clearance open and stable. It is estimated that at least 2/3 of the total machine mass corresponds to the supporting structure. The main aim of this investigation is to minimize the structural mass of a 3 MW direct-drive wind turbine permanent magnet electrical generator, which dimensions have been previously optimized, making use of topology optimization techniques. Easy to manufacture structures made of cast iron capable of complying with the requirements were generated for both rotor and stator.
Cross-comparative analysis of loads and power of pitching floating offshore wind turbine rotors using frequency-domain Navier-Stokes CFD and blade element momentum theory
Authors: Ortolani A. , Persico G. , Drofelnik J. , Jackson A. , Campobasso M.S.
Published: September 2020

Reliable predictions of the aero-and hydrodynamic loads acting on floating offshore wind turbines are paramount for assessing fatigue life, designing load and power control systems, and ensuring the overall system stability at all operating conditions. However, significant uncertainty affecting both predictions still exists. This study presents a cross-comparative analysis of the predictions of the aerodynamic loads and power of floating wind turbine rotors using a validated frequency-domain Navier-Stokes Computational Fluid Dynamics solver, and a state-of-the-art Blade Element Momentum theory code. The considered test case is the National Renewable Energy Laboratory 5 MW turbine, assumed to be mounted on a semi-submersible platform. The rotor load and power response at different pitching regimes is assessed and compared using both the high-and low-fidelity methods. The overall qualitative agreement of the two prediction sets is found to be excellent in all cases. At a quantitative level, the high-and low-fidelity predictions of both the mean rotor thrust and the blade out-of-plane bending moments differ by about 1 percent, whereas those of the mean rotor power differ by about 6 percent. Part of these differences at high pitching amplitude appear to depend on differences in dynamic stall predictions of the approaches.
Modelling of a wind-wave floating and semi-submersible power plant
Authors: Voltá Laura , Roqueta I , Thomas Sarah , Schmidt Paulsen Uwe
Published: September 2020

This paper exposes a method of modelling and analysis to help verifying design iterations of non-cylindrical shaped floating wind technologies. In order to do so, the Morison based quadratic hydrodynamic drag forcing contribution within the HAWC2-WAMIT coupled model, is modified to account for a panel-based input geometry. The implementation is applied to the P80 platform, and a verification of the hydrodynamic responses is performed. A reduced load case analysis is carried out, in which floating wind technologies can be assessed efficiently during early stage design iterations. The final platform assessment includes the wind and wave coupled effect using three load cases from IEC 61400-3 standards. The results of the simulations show that the chosen cases provide significant information relating to the platform motions and the tower top acceleration, in order to provide feedback for later design iterations of the platform.
A Comparison of Soil Structure Interaction Models for Dynamic Analysis of Offshore Wind Turbines
Authors: Fitzgerald Breiffni , Igoe David , Sarkar Saptarshi
Published: September 2020

This paper compares the dynamic response of an OWT structure where the below ground pile-soil behaviour is modelled using (i) the conventional API ‘p-y’ approach and (ii) the ‘PISA’ approach. A nonlinear aero-elastic code is used to model the structural dynamics of the OWT and coupled to the geotechnical model. The dynamic behaviour (natural frequencies) and fatigue loads of the turbine tower and monopile are estimated and compared using both the API and PISA approaches. A limited number of load cases were considered in the dynamic analysis with varied met-ocean conditions. It was found that the stiffer springs estimated by the PISA approach reduce the mean displacement of the tower in both the fore-aft and side-to-side directions. However, the increased monopile stiffness leads to a slightly increased amplitude of oscillations, particularly in the lightly damped side-to-side direction.
Predicting the occurrence of the vortex ring state for floating offshore wind turbines
Authors: Dong Jing , Viré Axelle
Published: September 2020

The local aerodynamic loading on floating offshore wind turbines (FOWTs) is more complex than on bottom-fixed wind turbines due to the platform motions. In particular, the FOWT rotor may start to interact with its own wake and enter a so-called vortex ring state (VRS). However, it is still unclear when, and to what extent, the VRS may happen to floating offshore wind turbines. In this paper, we quantitatively predict the VRS using Wolkovitch’s criterion during the operating conditions of different FOWTs simulated by FAST. The results show that the type of floating foundation has a significant influence on the aerodynamic performance of the rotor. Also, the probability of occurrence of VRS is bigger for the floating platforms that are more sensitive to wave excitations.
Wind turbine stability: Comparison of state-of-the-art aeroelastic simulation tools
Authors: Hach O , Verdonck H , Polman J D , Balzani C , Müller S , Rieke J , Hennings H
Published: September 2020

As rotor diameters and blade flexibility are increasing, current and future generation wind turbines are more susceptible to aeroelastic instabilities. It is thus important to know the prediction capabilities of state-of-the-art simulation tools in regards of the onset of aeroelastic instability. This article presents results of a code-to-code comparison of five different simulation codes using a representative wind turbine model. It is shown that the models are in good agreement in terms of isolated structural dynamics and steady state aeroelastics. The more complex the test cases become, the more significant are the differences in the results. In the final step of comparison, the aeroelastic stability limit is determined through a run-away analysis. The instability onset is predicted at different wind speeds and the underlying mechanisms differ between the tools. A Campbell diagram is used to correlate the findings of time domain simulation tools with those of a linear analysis in the frequency domain.
Validation of blade-resolved computational fluid dynamics for a MW-scale turbine rotor in atmospheric flow
Authors: Grinderslev Christian , Vijayakumar Ganesh , Ananthan Shreyas , Sørensen Niels N. , Zahle Frederik , Sprague Michael A.
Published: September 2020

In this study, simulation results of two different computational fluid dynamics codes, Nalu-Wind and EllipSys3D, are presented for a wind turbine rotor in complex yawed and sheared inflow. The results are compared to measurements from the DanAero experiments, to validate computed pressures and azimuthal trends. Despite different code methodologies and grid setups, the codes agree well in computed pressures and integrated forces along the blade for all blade azimuthal positions, however with some discrepancy in the very yawed case. Additionally, both codes capture well the azimuthal trends and force levels seen in measurements. Investigation into discrepancies shows that expanding grids before the rotor, lead to smearing of the wind profiles, which is likely the main cause of the differences in the results between the codes. Additionally, omission of the ground constraint cause discrepancies in relative velocity seen by the passing blade, due to an over speeding beneath the rotor.
The influence of leading edge roughness, rotor control and wind climate on the loss in energy production
Authors: Bak Christian , Forsting Alexander M. , Sorensen Niels N.
Published: September 2020

This study investigates how losses in energy production from wind turbines are influenced by leading edge roughness, rotor control and wind climates using computations. The performance of a NACA633-418 airfoil with five different damage types was predicted using Computational Fluid Dynamics (CFD) with bumps at the leading edge and grooves into the leading edge. Also, one type corresponding to a repair of a leading edge with an “overbite” was investigated. These airfoil characteristics were used in rotor computations where three different wind climates and five different maximum tip speeds were investigated. The rotor computations reflected that the Annual Energy Production (AEP) increased significantly with the average wind speed on the site. They also reflected that the relative AEP losses due to leading edge damages reduced with increasing average wind speed on sites. For the low wind speed site the losses were between 1% and 4% depending on the extent and the type of the blade damage. For the high wind speed site the losses were between 0.5% and 3%. Furthermore, the bigger the extent of the damages were the bigger the losses were. Finally, it was shown that increasing the maximum tip speed increased AEP and decreased the losses.
An experimental and numerical analysis of the dynamic variation of the angle of attack in a vertical-axis wind turbine
Authors: Melani P F , Balduzzi F , Brandetti L , Ferreira CJ Simão , Bianchini A
Published: September 2020

Simulation methods ensuring a level of fidelity higher than that of the ubiquitous Blade Element Momentum theory are increasingly applied to VAWTs, ranging from Lifting-Line methods, to Actuator Line or Computational Fluid Dynamics (CFD). The inherent complexity of these machines, characterised by a continuous variation of the angle of attack during the cycloidal motion of the airfoils and the onset of many related unsteady phenomena, makes nonetheless a correct estimation of the actual aerodynamics extremely difficult. In particular, a better understanding of the actual angle of attack during the motion of a VAWT is pivotal to select the correct airfoil and functioning design conditions. Moving from this background, a high-fidelity unsteady CFD model of a 2-blade H-Darrieus rotor was developed and validated against unique experimental data collected using Particle Image Velocimetry (PIV). In order to reconstruct the AoA variation during one rotor revolution, three different methods-detailed in the study-were then applied to the computed CFD flow fields. The resulting AoA trends were combined with available blade forces data to assess the corresponding lift and drag coefficients over one rotor revolution and correlate them with the most evident flow macro-structures and with the onset of dynamic stall.
Evaluating planetary boundary-layer schemes and large-eddy simulations with measurements from a 250-m meteorological mast
Authors: Peña Alfredo , Hahmann Andrea N.
Published: September 2020

We evaluate the performance of six planetary boundary layer (PBL) schemes and a large-eddy simulation (LES) for the characterization of the neutral PBL through idealized simulations using the Weather Research and Forecasting model. The evaluation is performed by comparison with sonic anemometer measurements from a 250-m tall meteorological tower that observes close-to-homogeneous winds under the predominant westerlies. All simulations show similar behavior for the vertical temperature profile except for one that uses a non-local PBL scheme, which is known to produce excessive vertical mixing. Within the range of measurements of the tower and except for a PBL scheme that produces a too low jet, the simulations using PBL schemes, which were developed to simulate the nighttime atmosphere, generally show the largest deviations from the observed wind speeds. As expected within the surface layer, the LES shows excessive vertical shear. More importantly, we find that two PBL schemes that use their own surface-layer scheme are effectively reducing the surface roughness. When looking at the vertical profile of momentum exchange coefficient, we find very good agreement between a local and a non-local PBL scheme within the bulk of the PBL, the highest values for the simulation with the PBL scheme showing excessive vertical mixing and the lowest values for that most suitable for nighttime conditions. The comparison with the observed turbulent kinetic energy reveals a good match between the LES and a simulation using a local PBL scheme and a general underestimation (overestimation) of turbulence within the range of measurements by the PBL schemes (LES).
Calibration of a super-Gaussian wake model with a focus on near-wake characteristics
Authors: Cathelain M. , Blondel F. , Joulin P.A. , Bozonnet P.
Published: September 2020

Offshore wind turbine near wakes can extend downstream up to 5D due to low atmospheric turbulence intensities. They are characterised by strong velocity deficits, a transitioning Gaussian shape, and strong added turbulence intensities. Classical analytical wake models are still used due to their low computational costs, but they mainly focus on far-wake characteristics. A super-Gaussian wake model valid in near-and far-wake regions has recently been developed at IFP Energies nouvelles. This wake model requires calibration and validation. To this end, large-eddy simulations of the large DTU-10MW reference wind turbine under different neutrally stratified atmospheric flows are carried out with the LES Meso-NH model. A database is generated based on these results and used to calibrate and validate the super-Gaussian model.
Analysing momentum balance over a large wind farm using a numerical weather prediction model
Authors: Lun Ma. , Dunstan Thomas D. , Nishino Takafumi
Published: September 2020

This study attempts to better understand the mechanisms of wind farm blockage effect by analysing momentum balance in realistic atmospheric flow over an idealised large offshore wind farm. The analysis is performed following the two-scale momentum theory, which predicts the importance of three different terms in the farm-scale momentum balance, namely the streamwise pressure gradient, Coriolis force and acceleration/deceleration terms. A numerical weather prediction (NWP) model is used as a realistic farm-scale flow model in this study to investigate how these three terms tend to change in time. Initial results suggest that the streamwise pressure gradient may be enhanced substantially by the resistance caused by the wind farm, whereas its influence on the other two terms appears to be relatively minor. These results suggest the importance of modelling the farm-induced pressure gradient accurately for various weather conditions in future studies of wind farm blockage.
Microscale CFD Simulations of a Wind Energy Test Site in the Swabian Alps with Mesoscale Based Inflow Data
Authors: Letzgus Patrick , Bahlouli Asmae El , Leukauf Daniel , Hofsäß Martin , Lutz Thorsten , Krämer Ewald
Published: September 2020

The current study describes analyses of the WINSENT wind energy test site located in complex terrain in Southern Germany by highly resolved numerical simulations. The resolved atmospheric turbulence is simulated with Delayed Detached Eddy Simulations by the flow solver FLOWer without consideration of the research wind turbines.

The mean inflow and wind direction of the analysed time period is provided by precursor simulations of project partners. The simulation model chain consists of three codes with different time scales and resolutions. The model chain provides a data transfer from mesoscale WRF simulations to OpenFOAM. As a next step OpenFOAM provides inflow data in the valley of the terrain site for the present FLOWer simulations, the code with the highest resolution in space and time. The mean velocity field provided by OpenFOAM is superimposed with fluctuations that are based on measurements to obtain the small turbulent scales within the FLOWer simulations, which the previous tools of the model chain can not resolve. Comparisons with the two already installed met masts clarify that the current FLOWer simulations provide an adequate agreement with measured data. The results are verified with the application of a second simulation, in which a homogeneous velocity profile is superimposed with turbulence. Thus, comparisons with measured data showed that the benefit of using the inflow data of this model chain is especially evident near the ground.
Non-deterministic wind observation from wind turbine loads
Authors: Bertelè M. , Bottasso C.L.
Published: September 2020

In this work, the wind sensing technology that exploits the turbine rotor as an anemometer is further developed into a non-deterministic formulation. First, an inflow-turbine response map is identified, which relates out and in-plane blade root bending moments to both vertical and horizontal shears and misalignments. Then, this linear model is used with and without a Kalman filter to estimate online the wind field at the rotor disk once blade loads are measured. A comprehensive simulation study, including different wind speeds and turbulence intensity levels, was performed to evaluate the accuracy of the new non-deterministic formulation. The results show that introducing a Kalman filter in the estimation process allows for a significant improvement in the angle estimates with respect to the deterministic formulation, with no considerable additional computational cost.
An adaptation of the super-Gaussian wake model for yawed wind turbines
Authors: Blondel Frèdèric , Cathelain Marie , Joulin Pierre-Antoine , Bozonnet Pauline
Published: September 2020

The wake of a yawed wind turbine tends to be deflected and does not follow the incoming wind direction. This phenomenon, often referred to as “wake deflection”, has recently received a lot of attention from the wind energy research community: it is possible to dynamically optimize a wind farm power production by yawing some turbines to deflect their wakes, thus minimizing wake losses over the whole wind farm. In the present work, an analytical model for estimating the deflection of a yawed wind turbine wake is proposed. This new model is based on a super-Gaussian shape assumption for the velocity profile, enabling the estimation of the wake deflection in both near and far wake regions. First, the super-Gaussian model will be briefly introduced. Then, the new wake deflection model will be presented, as well as an updated version of the well known Jimenez model. This revised model allows a proper comparison with the proposed super-Gaussian model, since it is based on a similar definition of the wake width. Finally, results will be compared with experimental data from the literature.
A Graph Neural Network Surrogate Model for the Prediction of Turbine Interaction Loss
Authors: Bleeg James
Published: September 2020

The current generation of wind farm flow models lacks an option that can efficiently and reliably account for both wake and blockage effects when calculating turbine interaction loss. Traditional wake models are fast but ignore blockage effects. High-fidelity flow models are more complete, but turnaround times can be relatively long. The objective of this study is a model that combines the speed of traditional models with the accuracy of higher-fidelity approaches. To this end, we use a graph neural network (GNN) as a surrogate model for a steady-state Reynolds Averaged Navier-Stokes (RANS) model. Comparisons reveal good agreement between the GNN and RANS results for the atmospheric conditions considered.
Large eddy simulation of wind turbine wakes using adaptative mesh refinement
Authors: Zeoli S. , Balarac G. , Bénard P. , Georis G. , Houtin-Mongrolle F. , Bricteux L.
Published: September 2020

The development of turbulent vortical wakes released downstream of wind turbines is a key physical phenomenon as it presents many technological implications for windfarm design and exploitation. The numerical prediction of these wakes constitutes a challenging problem as they involve the shedding of fine vortical structures, their instabilities, and interactions with an ambient turbulent flow. The capture of these complex, three dimensional, unsteady flow phenomena calls for a Large Eddy Simulation (LES) approach. Yet, the computational cost of a scale resolved LES can be huge and the mesh generation process is not obvious when the zones of interest are not known a-priori. Adaptive mesh refinement (AMR) allows generating Eulerian elements only in the regions of interest of the flow, where an action takes place. The AMR strategy proposed here uses the MMG3D library coupled with the YALES2 unstructured finite volume solver. The method is successfully demonstrated on two test cases, the NTNU blind test case for which experimental data exist and the reference NREL 5MW under dynamic yaw conditions.
Influence of turbulence anisotropy on RANS predictions of wind-turbine wakes
Authors: Luan Yuyang , Dwight Richard P.
Published: September 2020

Simulating wind-turbines in Reynolds-averaged Navier-Stokes (RANS) codes is highly challenging, at least partly due to the importance of turbulence anisotropy in the evolution of the wake. We present a preliminary investigation into the role of anisotropy in RANS simulations of vertical-axis turbines, by comparison with LES. Firstly an LES data-set serving as our ground-truth is generated, and verified against previously published works. This data-set provides raw turbulence anisotropy fields for several turbine configurations. This anisotropy is injected into RANS simulations of identical configurations to determine the extent to which it influences (i) the production of turbulence kinetic energy, (ii) the turbulence momentum forcing, and finally (iii) the mean-flow. In all these quantities we observe the anisotropy has a surprisingly limited effect, and is certainly not the leading-order error in Boussinesq RANS for these cases. Nevertheless we go on to show that it is feasible to predict anisotropy fields for unseen configurations based only on the mean-flow, by using a tensorized version of random-forest regression.
Dependence of wind turbine loads on inlet flow field
Authors: Hanssen-Bauer Ø. W. , de Vaal J. B. , Tutkun M. , Asmuth H. , Ivanell S. , Stenbro R.
Published: September 2020

In wind farm simulations, the inflow wind field plays a crucial role in the accuracy of both power production, structural load predictions and the turbulent wake development behind wind turbines. Three different inflow wind field generation techniques, namely the Mann model, a reduced order based model described herein and LES data, are used in this study to characterise the relation between the inflow and the structural response of the wind turbine. In addition, the wake development under different inflow conditions are studied. The turbulence statistics of the reduced-order model and the LES data are similar to each other while the Mann turbulence has different turbulence profiles and spectral characteristics. An in-house developed aeroelastic code, 3Dfloat, is used for structural response analysis. The differences between the inflow fields are mainly attributed to the turbulence intensity profiles, and differences in their spectral characteristics.
Modelling cluster wakes and wind farm blockage
Authors: Nygaard Nicolai Gayle , Steen Søren Trads , Poulsen Lina , Pedersen Jesper Grønnegaard
Published: September 2020

We present two new models for wind turbine interaction effects and a recipe for combining them. The first model is an extension of the Park model, which explicitly incorporates turbulence, both the ambient atmospheric turbulence and the turbulence generated in the wake itself. This Turbulence Optimized Park model is better equipped to describe wake recovery over long distances such as between wind farms, where the wake expansion slows down as the turbine-generated turbulence decays. The second model is a first version of a full engineering wind farm blockage model. In the same vein as the wake model it adds blockage contributions from the individual wind turbines to form an aggregated wind farm scale blockage effect that can be incorporated directly into the park power curve and annual energy calculations. The wake model and the blockage model describe downstream and upstream turbine interaction effects, respectively. They are coupled as the outputs of one model are the inputs to the other model and vice versa. We describe how this coupling is achieved through an iterative process. We give early stage examples of the validation of the two models and discuss how they might be further validated and improved in the future.
Participatory mapping of hydro-meteorological hazard-prone locations
Authors: Sumadio W , Hidayat A , Zubair A , Tampi D M , Lisanyoto L , Fitrinitia I S
Published: September 2020

Community concepts and terms often appear in policies and programs related to environmental issues and community participation. During this time, the concept of community uses the location of residence as the basis for its determination. The assumption is that those who live in these locations are the most familiar with their surroundings. The high displacement of urban residents causes some of them do not always know the place of their residence. This condition can affect the success of development programs that involve the community. To help implementing the program successfully, training on community participation-based map development is needed. The objective of this paper is to offers a way to find out people’s perceptions of where they live, so that they have a collective awareness of their environment through map development. Researchers conducted training of 15 residents who were members of the Kancil community. Kancil community located in a settlement on the edge of Ci Liwung, Depok City, West Java. Data of the environment is collected by mapping the location of a settlement area by several methods. The results of the mapping with the theme of hydro-meteorological disaster sensitivity were integrated subsequently into the form collaborative mapping. This participatory mapping produced a map showing the boundaries of flooded areas, areas prone to clean water scarcity, and locations prone to landslides. Community participation-based map development shows the people’s perception of their environment. Individu with high travel pattern shows knowledge and awareness on their environment. The mental map has a positive influence to their knowledge.
Detection of deforestation and analysis land conversion from high resolution satellite imageries in Bintulu District, Serawak, Malaysia
Authors: Aik D H J , Ismail M H
Published: September 2020

Primary forests are continuously threatened day to day by urbanisation and the conversion to agricultural plantation such as palm oil production and other land uses being one of the major reasons. In South-East Asia, the widespread of oil palm has boomed over the last two decades, resulting in the downfall of tropical forest land. This change has been particularly prevalent in Borneo with protected lands increasingly developed for palm oil and already deforested lands are being converted into industrial plantations. The primary concerns relating to this pattern of land use change are the short and long-term impacts of logging on our natural environments and ecosystems and how patterns of deforestation are contributing to global environment issues such as climate change. By detecting and mapping logging activities, forestry departments are better able to predict land cover changes in a particular region as a result of development and deforestation. In this study, land cover assessment based on remote sensing techniques was used to analyse changes in the Bintulu district, Borneo especially oil palm growth and its influence on the decline of forest areas between 2016 and 2018. High resolution satellite imageries (3 m spatial resolution) from PlanetScope were used due to the benefits in helping to differentiate several land cover classes over a higher spatial resolution. Results showed that a decline of primary forests in Bintulu is about 26.5% over the past 2 years. With that decline, comes a rise of oil palm growth by 17.6% just within 2 years. An increased in logged areas (36.1%) for conversion to other land-covers with a steady decline of other land cover classes by at least 20% each year was detected. The accuracy of results proved a reasonable accuracy with 90.0% confidence with satellite imagery. Thus, with the result a necessary step can be considered to monitor and prevent deforestation and various encroachment in the forest. With high-resolution satellite data, monitoring at local scales has become possible to resource managers as a way to create timely and reliable assessments.
The attractiveness of malls for millennial consumer (Case study: Malls in BSD City)
Authors: Tadiarus N D , Setiadi H , Rizqihandari N
Published: September 2020

Property development, especially malls, continues to make shopping malls in BSD City becoming more diverse. The diversity of these malls is tailored to the needs of various millennial consumers as well. However, the variety of needs based on the diversity of ages and socio-economic status are influenced by motivation and intensity of millennial consumer visits to all malls in BSD. This makes the malls must have attraction to bring millennial consumers to visit. This research aimed to analyze the attractiveness of malls in BSD and the pattern of visits of millennial consumers influenced by the attractiveness of the mall. The variables of this study include location characteristics, concept of the mall and community experience as well as millennial consumer characteristics, motivation to visit the mall and sources of information. The method used in this study is descriptive analysis. The results of the study show that different characteristics of Malls in BSD City make each of them has a different attraction. The difference in attractiveness can influence the pattern of millennial consumer visits related to motivational factors, socio-economic status and sources of information owned by each consumer.