Full-scale Wind Research Articles

A finite difference approach to despiking in-stationary velocity data - tested on a triple-lidar

A novel despiking method is presented for in-stationary wind lidar velocity measurements. A finite difference approach yields the upper and lower bounds for a valid velocity reading. The sole input to the algorithm is the velocity series and optionally a far- field reference to the temporal variation in the velocity. The new algorithm is benchmarked against common despiking algorithms using a dataset acquired by three synchronised lidars in the upstream area of a full-scale wind turbine rotor and an artificially created space-time series with controlled spike contamination. By accounting for variations in space and time, this approach yields improvements in spike detection for in-stationary lidar measurements of about 25% over other more established stationary methods. Furthermore it proofs to be robust even for large numbers of spikes.

Speed Sensorless Control For Full-Scale Converter Of Wind Turbine With Induction Generator

This paper presents a speed sensorless control strategy for full-scale converter of wind turbine with the squirrel-cage induction generator (SCIG) based on a Model Reference Adaptive System (MRAS) method. The full-scale converter wind turbine has many advantages, such as simple structure, high reliability, low maintenance cost. However, there are still some drawbacks in its traditional control strategy, such as control stability, system performance, efficiency and reliability. The project implementation about generator speed estimation based on MRAS method is studied, and DC bias suppression is described completely based on the characteristics of SCIG. The Simulation experimental results show a consistency that is mainly in the correctness of flux observer design, the effectiveness of speed sensorless implementation strategy and good static and dynamic properties in the system.

Partial turbulence simulation method for predicting peak wind loads on small structures and building appurtenances

Large-scale wind tunnel testing is preferred for small structures and building appurtenances for maintaining modeling accuracy and minimizing Reynolds number effects. In these circumstances the ability to obtain a large enough turbulence integral scale is usually compromised by the limited dimensions of the wind tunnel. So, it is not normally possible to fully simulate the low frequency end of the turbulence spectrum. In this paper the approach is taken of dividing the turbulence into two distinct statistical processes, one at high frequencies which can be simulated in the wind tunnel, and one at low frequencies which can be treated in post-test analysis using the assumptions of quasi-steady theory. In this Partial Turbulence Simulation (PTS) method the contribution of both the high and low frequency turbulence on the wind loads on structures is included by using the probability of load from each of the two processes, with one part coming from the wind tunnel data representing the high frequency component and the remainder from the assumed probability distribution (taken in this paper as Gaussian for generic boundary layer flow) of the missing low frequency component. The two processes are approximated as independent of each other. The efficacy and validity of the method and its various assumptions are assessed by comparing predicted local peak pressure coefficients from tests on large scale models of the Silsoe cube and Texas Tech University (TTU) building in the Wall of Wind facility at Florida International University (FIU) with the corresponding full-scale data. Generally good agreement was found between the model results and full scale, particularly when comparing the highest overall peak pressure coefficients. These results, although limited to peak local pressures on the two test buildings for which good full scale data are available, are encouraging and invite further experiments to explore the range of applicability of the PTS method. This method, although developed in the Wall of Wind facility at FIU, can be equally used in conventional boundary layer wind tunnels and has the potential to enhance the ability of existing boundary layer wind tunnel facilities to predict full scale wind loads.

Parameter Estimation of Unmanned Flight Vehicle Using Wind Tunnel Testing and Real Flight Data

AbstractThe work presented in this paper addresses the longitudinal parameter estimation of an unmanned configuration using wind tunnel testing and flight data. For this purpose, an unmanned aerial vehicle has been designed with a cropped delta planform and rectangular cross-section. Exhaustive full-scale wind tunnel tests were carried out on the designed unmanned flight vehicle to capture the linear and nonlinear variation of aerodynamic force and moment coefficients. The measured wind tunnel test data, in the form of signals, have been processed to forces and moments about the desired reference point of the designed unmanned platform. A comprehensive discussion on the obtained results from wind tunnel testing has been presented. In order to enhance the confidence in the generated aerodynamic database from wind tunnel testing and also to estimate the dynamic derivatives, two sets of real flight data pertaining to longitudinal dynamics (acquired during the flight tests) have been used. The parameter estim...

Wind effects on a cable-suspended roof: Full-scale measurements and wind tunnel based predictions

Full-scale measurements of wind effects on a long-span cable-suspended roof were carried out. The wind-induced response data were analyzed in the time-frequency domain based on the wavelet transformation, and modal frequencies and amplitude-dependent damping ratios were identified with the random decrement technique. The damping ratios were noted larger with increasing response amplitude especially in the fundamental mode. The identified modal frequencies from the full-scale measurements were lower than those from the original finite element model (FE model). The identified modal parameters were then used to update the FE model with an artificial neural networks (ANNs) based scheme. The dynamic response from the roof was computed from the updated FE model of the structure where the wind loads input was obtained from simultaneous pressure measurement in wind tunnel tests. In view of the uncertainties surrounding both full scale measurements and wind tunnel based predictions, these comparisons show good agreements at least at two locations. Both the dynamic response from full-scale measurements and numerically predicted analyses demonstrated significant contributions from multi-mode effects. The computed response spectra at selected locations were similar to those from the full-scale measurements, suggesting a validation of the predictions.

Assessment and Enhancement of a Full-Scale PMSG-Based Wind Power Generator Performance Under Faults

A full-scale permanent-magnet synchronous generator (PMSG)-based wind turbine with dc-link voltage control via the machine-side converter has the potential to provide inherent low-voltage ride-through (LVRT) performance without additional hardware components. However, several important performance aspects related to this topology are not addressed in this literature. This paper investigates the impacts of the LVRT control on the stability and risk of resonance, successful operation, and fatigue in a full-scale PMSG-based wind power generation system. An analytical model, considering the double-mass nature of the turbine/generator and typical LVRT requirements, is developed, validated, and used to characterize the dynamic performance of the wind generation system under LVRT control and practical generator characteristics. To enhance the operation and reduce the fatigue under LVRT control, two solutions, based on active damping control and dc-link voltage bandwidth retuning, are proposed, analyzed, and compared. The detailed nonlinear time-domain simulation results validate the accuracy of the developed model and analytical results.

Impact vibration test of monopile foundation model in dry sand

Measurements on full-scale offshore wind turbines have shown that the horizontal foundation stiffness for monopiles is underpredicted by current design methods. This paper presents a 1:20 model scale test of a monopile foundation for offshore wind turbines, installed in dry laboratory sand. The test is performed under fully controlled laboratory conditions, with low-stress soil effects minimised by overburden pressures applied by a vacuum system. Soil–pile interaction stiffness is indirectly measured by eigenfrequencies in a free vibration test, with vibration initiated by a horizontal impact load to the top of the pile. The purpose of the test is to provide a benchmark for evaluation of calculation methods for laterally loaded monopile foundations. Results for system eigenfrequency and system damping are presented along with measurements of small-strain stiffness for the laboratory sand. Pile displacement profiles are derived for different oscillation amplitudes, on the basis of a numerical beam model, accelerometer and strain gauge measurements. A relationship between small-strain soil stiffness and eigenfrequency is identified. The measured system eigenfrequencies and system damping are found to depend on the applied surcharge pressure and the displacement amplitude.

Initiation of trailing edge failure in full-scale wind turbine blade test

The reliability and accuracy of a numerical shell model simulation and its predictive capabilities with existing failure criteria are compared to experiments of a 34m long blade tested to ultimate failure. Strengths and weaknesses of in-plane failure criteria are highlighted and the geometrical non-linear buckling effect of the trailing edge under combined loading, and how it affects the ultimate strength of a blade in a trailing-edge failure dominated load direction were investigated. The study details the interaction between trailing edge buckling on damage onset and sandwich panel failure. The numerically applied fracture mechanics approaches showed good agreement with the experimental results.

Experiments on the Performance of Small Horizontal Axis Wind Turbine with Passive Pitch Control by Disk Pulley

The present work is to design a passive pitch-control mechanism for small horizontal axis wind turbine (HAWT) to generate stable power at high wind speeds. The mechanism uses a disk pulley as an actuator to passively adjust the pitch angle of blades by centrifugal force. For this design, aerodynamic braking is caused by the adjustment of pitch angles at high wind speeds. As a marked advantage, this does not require mechanical brakes that would incur electrical burn-out and structural failure under high speed rotation. This can ensure the survival of blades and generator in sever operation environments. In this paper, the analysis uses blade element momentum theory (BEMT) to develop graphical user interface software to facilitate the performance assessment of the small-scale HAWT using passive pitch control (PPC). For verification, the HAWT system was tested in a full-scale wind tunnel for its aerodynamic performance. At low wind speeds, this system performed the same as usual, yet at high wind speeds, the equipped PPC system can effectively reduce the rotational speed to generate stable power.

Energy efficiency tests in a full scale wind turbine gearbox

A 850kW wind turbine gearbox, widely used in wind farms, was used to perform efficiency tests of different wind turbine gear oil formulations.One mineral and three polyalpholephin commercially available lubricants were chosen, all them are ISO VG 320 wind turbine gear oils.Study the influence of different gear oil technologies in the overall gearbox transmission efficiency is the main objective of this work.The results show that different energetic efficiency and different oil particle counting were obtained even when the same base oil is used.

Full-field assessment of wind turbine near-wake deviation in relation to yaw misalignment

Abstract. Presently there is a lack of data revealing the behaviour of the path followed by the near wake of full scale wind turbines and its dependence on yaw misalignment. Here we present an experimental analysis of the horizontal wake deviation of a 5 MW offshore wind turbine between 0.6 and 1.4 diameters downstream. The wake field has been scanned with a short-range lidar and the wake path has been reconstructed by means of two-dimensional Gaussian tracking. We analysed the measurements for rotor yaw misalignments arising in normal operation and during partial load, representing high thrust coefficient conditions. We classified distinctive wake paths with reference to yaw misalignment, based on the nacelle wind vane, in steps of 3° in a range of ±10.5°. All paths observed in the nacelle frame of reference showed a consistent convergence towards 0.9 rotor diameters downstream, suggesting a kind of wake deviation shift. This contrasts with published results from wind tunnels which in general report a convergence towards the rotor. The discrepancy is evidenced in particular in a comparison which we performed against published paths obtained by means of tip vortex tracking.

A time-dependent Eulerian model of droplet diffusion in turbulent flow

Industrial sprays are common in many operations where liquid application to surfaces is required. Maximization of the spray process efficacy depends on accurate simulation of spray characteristics and surrounding flow conditions. Traditionally, droplet modeling has been performed using a Lagrangian approach which requires tracking a sufficient number of droplets to form statistical estimates of droplet deposition. Alternatively for this study, an Eulerian-based flow and droplet transport model using the Direct Quadrature Method of Moments (DQMOM) is applied to spray modeling and is coupled with the Reynolds Averaged Navier Stokes (RANS) equations and Shear Stress Transport (SST) turbulence model. A new turbulent diffusion model is developed for droplet transport which accounts for inertia and time-limit effects and covers a wide range of operational parameters associated with aerial spraying. The model is based on a full parametric study using Lagrangian particle tracking in a uniform, homogeneous and isotropic turbulent flow field and is subsequently implemented within the Eulerian DQMOM framework and compared to: 1) Lagrangian tracking predictions of a log-normal particle size distribution injected into a homogeneous, isotropic turbulent flow field, and 2) full-scale experimental wind tunnel measurements in the anisotropic, non-homogeneous wake of a hollow cone hydraulic nozzle.

Circulating current control strategy for parallel full‐scale wind power converters

Converter parallel techniques can increase the power rating, but there is a circulating current problem. Therefore, this study focuses on the circulating current problem in parallel full-scale wind power converter systems. The general definition of circulating currents is first introduced. The concept of circulating current percentage is then defined to quantitatively analyse the relatively serious situation of circulating currents for parallel converter systems. Then, the generation mechanisms of circulating currents are analysed based on the mathematical model of circulating currents. Actually, circulating currents can be regarded as a kind of disturbance to the load currents of a parallel system. Thereby, a novel control strategy, based on circulating current feed-forward compensation for parallel converter systems, is proposed and a feed-forward controller is designed. Finally, simulations based on MATLAB/Simulink and hardware-in-loop experiments based on RT-LAB are carried out. Both simulation and experimental results validate the proposed circulating current control method.

Unsteady aerodynamics simulation of a full-scale horizontal axis wind turbine using CFD methodology

The aerodynamic performance of wind turbines is significantly influenced by the unsteady flow around the rotor blades. The research on unsteady aerodynamics for Horizontal Axis Wind Turbines (HAWTs) is still poorly understood because of the complex flow physics. In this study, the unsteady aerodynamic configuration of a full-scale HAWT is simulated with consideration of wind shear, tower shadow and yaw motion. The calculated wind turbine which contains tapered tower, rotor overhang and tilted rotor shaft is constructed by making reference of successfully commercial operated wind turbine designed by NEG Micon and Vestas. A validated CFD method is utilized to analyze unsteady aerodynamic characteristics which affect the performance on such a full-scale HAWT. The approach of sliding mesh is used to carefully deal with the interface between static and moving parts in the flow field. The annual average wind velocity and wind profile in the atmospheric border are applied as boundary conditions. Considering the effects of wind shear and tower shadow, the simulation results show that the each blade reaches its maximum and minimum aerodynamic loads almost at the same time during the rotation circle. The blade–tower interaction imposes great impact on the power output performance. The wind turbine produces yaw moment during the whole revolution and the maximum aerodynamic loads appear at the upwind azimuth in the yaw computation case.

Turbulent airflow above a full-scale macroporous material: Boundary layer characterization and conditional statistical analysis

Convective drying of macroporous materials is governed by the complex interaction between airflow above and into the material, the roughness of the air–material interface and the characteristics of the material pore system. In this study, we experimentally investigate this interplay in detail and at full-scale, using porous asphalt (PA) as a model material. The characteristics of the turbulent flow in the immediate vicinity of the material surface are studied with full-scale wind tunnel experiments at three flow speeds over two types of PA with different surface porosities and surface pore sizes, and are compared to similar measurements over a smooth and impermeable reference material. It is shown that, above a certain wall-normal distance, turbulence profiles can be scaled to make them independent of the flow speed. However, at low speed, the scaling breaks down due to a combination of organized turbulent structures of high intensity and a low turbulence background. No generally valid scaling applicable at all tested air speeds is found close to the surface, where drying occurs. Hence, realistic drying experiments must be performed at full scale and for the entire range of velocities of interest.

Monitoring of Wind Turbine Gearbox Condition through Oil and Wear Debris Analysis: A Full-Scale Testing Perspective

ABSTRACTDespite the wind industry's dramatic development during the past decade, it is still challenged by premature turbine subsystem/component failures, especially for turbines rated above 1 MW. Because a crane is needed for each replacement, gearboxes have been a focal point for improvement in reliability and availability. Condition monitoring (CM) is a technique that can help improve these factors, leading to reduced turbine operation and maintenance costs and, subsequently, lower cost of energy for wind power. Although technical benefits of CM for the wind industry are normally recognized, there is a lack of published information on the advantages and limitations of each CM technique confirmed by objective data from full-scale tests. This article presents first-hand oil and wear debris analysis results obtained through tests that were based on full-scale wind turbine gearboxes rated at 750 kW. The tests were conducted at the 2.5-MW dynamometer test facility at the National Wind Technology Center at the National Renewable Energy Laboratory. The gearboxes were tested in three conditions: run-in, healthy, and damaged. The investigated CM techniques include real-time oil condition and wear debris monitoring, both inline and online sensors, and offline oil sample and wear debris analysis, both onsite and offsite laboratories. The reported results and observations help increase wind industry awareness of the benefits and limitations of oil and debris analysis technologies and highlight the challenges in these technologies and other tribological fields for the Society of Tribologists and Lubrication Engineers and other organizations to help address, leading to extended gearbox service life.

Wind Speed and Direction Detection by Means of Solid-state Anemometers Embedded on Small Quadcopters

This work describes the application of a compact, MEMS-based, 2D anemometer to the estimation of a quadrotor's airspeed. Correcting for the vehicle's ground speed provided by internal GPS and inertial units allows this low cost, mobile platform to provide local wind speed estimates. A series of initial, bench-top tests were performed to characterize and calibrate the sensor, which is an improved version of a recently proposed and novel device. Additional full-scale wind tunnel experiments were performed with the sensor mounted on a fixed quadrotor to test the effect of the propellers on the sensor's performance.

Sliding Mode Control of a Hydraulically Actuated Load Application Unit With Application to Wind Turbine Drivetrain Testing

This paper presents a sliding mode control strategy for a load application unit (LAU) found at Clemson University’s Wind Turbine Drivetrain Testing Facility in North Charleston, SC, USA. The LAU is a multiinput, multioutput, overactuated, nonlinear, dynamic system and is part of a 7.5-MW wind turbine nacelle test bench. First, a plant model of the system is developed. Second, a sliding mode control strategy is developed. This control strategy uses a pseudoinverse of the input influence matrix to account for the system being overactuated. The resulting reference signals are inputs to a sliding controller responsible for controlling the system’s 24 hydraulic actuators. The results show that the proposed control strategy performs well and that the LAU may be suitable for replicating full-scale time-varying wind loads on the main shaft of a test nacelle. Also discussed are key areas for improvement and future research directions.

Static test until structural collapse after fatigue testing of a full-scale wind turbine blade

The effect of fatigue damage on the residual strength of a large wind turbine blade is a very important issue in the wind industry. To test the residual strength after fatigue testing, this study prepared a test specimen, a 48.3m wind turbine blade that had experienced initial static tests and then fatigue tests in accordance with the technical specification IEC TS 61400-23. The prepared specimen was loaded sequentially along the positive flapwise, the positive edgewise, and the negative flapwise direction, while video-recording the test situations. The wind turbine blade was able to sustain the loads in the first two tests, but the blade collapsed in the third test when the negative flapwise load reached 70% of the maximum target value, a value representing 50% of the most severe load in the first test. Based on the recorded information and the fracture patterns at the blade’s broken section, the collapse processes were analyzed. From this analysis we suggest a modified laminate pattern that can enhance the residual strength of a fatigue damaged wind turbine blade.

Wind Speed Dependency of Low-Frequency Vibration Levels in Full-Scale Wind Turbines

A series of continuous vibration measurements in 14 upwind wind turbines of the same model and belonging to the same wind farm have been conducted. The data were acquired over a period lasting approximately half a year. The tower axial vibration acceleration has been monitored in the frequency band from 0 to 10 Hz with an accelerometer mounted on the gearbox casing between the intermediate and the high-speed shafts. It has been observed that the average frequency spectrum is dominated by the blade passing frequency in all the wind turbines. The evolution of the vibration magnitudes over the entire range of operating conditions is also very similar for all the wind turbines. The root-mean-square (rms) acceleration value has been correlated with the wind speed, and it has been found that a linear fit with a positive slope is a useful model for prediction purposes.