Turbine Nacelle Research Articles

Wavelet and Hilbert Huang transform based wind turbine imbalance fault classification model using <i>k</i>-nearest neighbour algorithm

Wind turbine (WT) is a key part in wind power generator system (WTGs). For proper operation, condition monitoring and fault diagnosis is a major part in WTGs. In this paper, three different types of nacelle yaw faults along with healthy condition are analysed using wavelet transform (WT) and Hilbert Huang transformed (HHT) based k-nearest neighbour (k-NN) algorithm. For decomposing the raw signals, discrete approximation of Meyer wavelet function (DMeyer/dmey) is used and to extract the feature, Hilbert Huang transform is used to find the amplitude and phase feature of decomposed signal. k-nearest neighbour algorithm based classifier is designed for classifying faults based on extracted features. Prepared feature matrix of twenty one attributes is used for wind turbine nacelle yaw imbalance fault classification. The proposed technique is being compared with other computational intelligence dependent techniques of artificial neural network (i.e., multilayer perceptron-MLP). Results and different comparisons of proposed technique could work as an essential tool for fault diagnosis of WTGs.

南大隅WF 風車ナセルカバー飛散・損傷事故の再発防止に向けた強度対策検討

南大隅WF 風車ナセルカバー飛散・損傷事故の再発防止に向けた強度対策検討

Pyrolysis Properties and Kinetics of Typical Liquid Oils in Wind Turbine Nacelle

Abstract To evaluate fire risk of typical liquid oils applied in nacelle of wind turbine, pyrolysis properties prior to combustion should be known. Pyrolysis properties of three kinds of typical oils of hydraulic oil, gearbox oil and transformer oil were studied by using Thermogravimetry (TG)- Differential Scanning Calorimetry (DSC) technique. Pyrolysis kinetics was analyzed. Apparent activation energy and pre-exponential factor were calculated by using Kissinger method. Results show that according to the TG-DSC analysis, for all three oils, the pyrolysis processes can be divided into three stages. The first stage is evaporation from room temperature to 140.1 °C (gearbox oil), 123.4 °C (transformer oil), and 144.1 °C (hydraulic oil). The second stage is the primary mass loss stage, corresponding temperature is in the range of 140.1–542.0 °C (gearbox oil), 123.4–294.1 °C (transformer oil), and 144.1–329.5 °C (hydraulic oil), among which the temperature of maximum heat mass loss rate of gearbox oil, transformer oil and hydraulic oil is 402.6, 220.1 and 262.6 °C. The third stage is the end of char oxidation and mass of residual char is kept constant, the temperature is higher than 542.0, 294.1, and 329.5 °C. Activation energies and pre-exponential factors were obtained by kinetic analysis, according to the pyrolysis kinetics analysis, the hydraulic oil is more prone to be pyrolyzed than gearbox oil and transformer oil and this provides a basis for judging the combustion characteristics of oil products by pyrolysis kinetic parameters in the future.

Numerical investigations of laminar buoyant heat transfer in a 2D-enclosure – Application to wind turbine nacelle operating in hot climate

The climate of the Algerian Sahara is characterized by extremethermal conditions. The wind turbines installed in theSahara, namely the electromechanical equipment located insidethe nacelle (e.g. electrical generator), are subjected to high andfluctuating temperature gradients during the day and the seasons.This reality might generate contradictory constraints of designand can lead to some difficulties of conception. In order to maintainan appropriate temperature of the air inside the nacelle (i.e.acceptable average temperature of the electromechanical equipment),the heat generated by the generator must be rejected towardsthe environment, and the resulting heat transfer must becontrolled properly. This work deals with heat transfer effectswithin a reduced scale nacelle, i.e. hypothetical nacelle. Forthis purpose, a small nacelle dimensions has been considered andrepresented as rectangular cavity. In this paper, the air flow fieldswithin the nacelle have been described using the Navier-Stokesequations. The energy equation has been used to account for heattransfer effects. ANSYS FLUENT code has been employed tosolve the resulting governing equations. The main object of thiswork is to determine the average temperature inside the nacelle,as well as to investigate its variation with the required coolingcapacity.DOI: http://dx.doi.org/10.5755/j01.mech.23.5.15815

Active structural control of a floating wind turbine with a stroke-limited hybrid mass damper

Floating wind turbines are subjected to more severe structural loads than fixed-bottom wind turbines due to additional degrees of freedom (DOFs) of their floating foundations. It's a promising way of using active structural control method to improve the structural responses of floating wind turbines. This paper investigates an active vibration control strategy for a barge-type floating wind turbine by setting a stroke-limited hybrid mass damper (HMD) in the turbine's nacelle. Firstly, a contact nonlinear modeling method for the floating wind turbine with clearance between the HMD and the stroke limiters is presented based on Euler-Lagrange's equations and an active control model of the whole system is established. The structural parameters are validated for the active control model and an equivalent load coefficient method is presented for identifying the wind and wave disturbances. Then, a state-feedback linear quadratic regulator (LQR) controller is designed to reduce vibration and loads of the wind turbine, and two optimization methods are combined to optimize the weighting coefficients when considering the stroke of the HMD and the active control power consumption as constraints. Finally, the designed controllers are implemented in high fidelity simulations under five typical wind and wave conditions. The results show that active HMD control strategy is shown to be achievable and the designed controllers could further reduce more vibration and loads of the wind turbine under the constraints of stroke limitation and power consumption. “V”-shaped distribution of the TMD suppression effect is inconsistent with the Weibull distribution in practical offshore floating wind farms, and the active HMD control could overcome this shortcoming of the passive TMD.

Comparison of wind farm large eddy simulations using actuator disk and actuator line models with wind tunnel experiments

We compare wind farm large eddy simulations with the EPFL wind tunnel measurement by Chamorro and Porté-Agel (Bound-Lay. Meteorol. 136, 515 (2010) and Energies 4, 1916 (2011)). We find that the near turbine wake, up to 3 turbine diameters downstream, of a single turbine is captured better with the actuator line method than using the actuator disk method. Further downstream the results obtained with both models agrees very well with the experimental data, confirming findings from previous studies. For large aligned wind farms we find that the actuator disk model predicts the wake profiles behind turbines on the second and subsequent rows more accurately than the wake profile behind the first turbine row. The reason is that the wake layer profile that is created at hub height in very large wind farms is closer to the assumptions made in the actuator disk model than the logarithmic profile found in the inflow conditions. In addition, we show that, even in relatively coarse resolution simulations, adding the effect of the turbine nacelle and tower leads to a significant improvement in the prediction of the near wake features at 1 and 2 diameters downstream.

Hybrid, Multi-Megawatt HVDC Transformer Topology Comparison for Future Offshore Wind Farms

With the wind industry moving further offshore, High Voltage Direct Current (HVDC) transmission is becoming increasingly popular. HVDC transformer substations are not optimized for the offshore industry though, increasing costs and reducing redundancy. A suggested medium frequency, modular hybrid HVDC transformer located within each wind turbine nacelle could mitigate these problems, but the overall design must be considered carefully to minimize losses. This paper’s contribution is a detailed analysis of the hybrid transformer, using practical design considerations including component library minimization. The configurations investigated include combinations of single phase H-Bridge and Modular Multilevel Converter topologies operating under minimum switching frequency control strategies. These were modelled in the MATLAB/Simulink environment. The impact of the minimum switching control strategy and converter topology on power transfer stability and overall efficiency is then investigated. It was found that the H-Bridge converter generated the lowest overall losses, but there was a trade off with power flow sensitivity due in part to the additional harmonics generated.

Defect characterisation of tensile loaded CFRP and GFRP laminates used in energy applications by means of infrared thermography

The increased use of fibre reinforced plastic (FRP) composites for improved efficiency and reliability in energy related applications, e.g. wind and marine turbine blades, nacelles, oil and gas flexible risers, also increases the demand for innovative non-destructive testing technologies. In this contribution, results concerning the characterisation of CFRP and GFRP during and after quasi-static tensile loading are presented. It includes the measurement of optical properties in the infrared spectral range, tensile loading tests with the observation of the temperature distribution at one or both sides of the specimens using an infrared camera for the preparation and monitoring of intended natural defects, and active thermography inspections after tensile loading. It is shown that the defect preparation was successful. Thermographic monitoring during and active thermography testing after tensile loading enable the detection of the lateral extend of the generated defects. Differences between CFRP and GFRP materials are discussed.

Wind tunnel investigation on the effect of the turbine tower on wind turbines wake symmetry

AbstractIn wind farms, the wake of the upstream turbines becomes the inflow for the downstream machines. Ideally, the turbine wake is a stable vortex system. In reality, because of factors like background turbulence, mean flow shear, and tower‐wake interaction, the wake velocity deficit is not symmetric and is displaced away from its mean position. The irregular velocity profile leads to a decreased efficiency and increased blade stress levels for the downstream turbines. The object of this work is the experimental investigation of the effect of the wind turbine tower on the symmetry and displacement of the wake velocity deficit induced by one and two in‐line model wind turbines (,D= 0.9 m). The results of the experiments, performed in the closed‐loop wind tunnel of the Norwegian University of Science and Technology in Trondheim (Norway), showed that the wake of the single turbine expanded more in the horizontal direction (side‐wall normal) than in the vertical (floor normal) direction and that the center of the wake vortex had a tendency to move toward the wind tunnel floor as it was advected downstream from the rotor. The wake of the turbine tandem showed a similar behavior, with a larger degree of non‐symmetry. The analysis of the cross‐stream velocity profiles revealed that the non‐symmetries were caused by a different cross‐stream momentum transport in the top‐tip and bottom‐tip region, induced by the turbine tower wake. In fact, when a second additional turbine tower, mirroring the original one, was installed above the turbine nacelle, the wake recovered its symmetric structure. Copyright © 2017 John Wiley & Sons, Ltd.

Numerical and Experimental Study of Wake Redirection Techniques in a Boundary Layer Wind Tunnel

The aim of the present paper is to validate a wind farm LES framework in the context of two distinct wake redirection techniques: yaw misalignment and individual cyclic pitch control. A test campaign was conducted using scaled wind turbine models in a boundary layer wind tunnel, where both particle image velocimetry and hot-wire thermo anemometers were used to obtain high quality measurements of the downstream flow. A LiDAR system was also employed to determine the non-uniformity of the inflow velocity field. A high-fidelity large-eddy simulation lifting-line model was used to simulate the aerodynamic behavior of the system, including the geometry of the wind turbine nacelle and tower. A tuning-free Lagrangian scale-dependent dynamic approach was adopted to improve the sub-grid scale modeling. Comparisons with experimental measurements are used to systematically validate the simulations. The LES results are in good agreement with the PIV and hot-wire data in terms of time-averaged wake profiles, turbulence intensity and Reynolds shear stresses. Discrepancies are also highlighted, to guide future improvements.

Large-Eddy Simulation of Waked Turbines in a Scaled Wind Farm Facility

The aim of this paper is to present the numerical simulation of waked scaled wind turbines operating in a boundary layer wind tunnel. The simulation uses a LES-lifting-line numerical model. An immersed boundary method in conjunction with an adequate wall model is used to represent the effects of both the wind turbine nacelle and tower, which are shown to have a considerable effect on the wake behavior. Multi-airfoil data calibrated at different Reynolds numbers are used to account for the lift and drag characteristics at the low and varying Reynolds conditions encountered in the experiments. The present study focuses on low turbulence inflow conditions and inflow non-uniformity due to wind tunnel characteristics, while higher turbulence conditions are considered in a separate study. The numerical model is validated by using experimental data obtained during test campaigns conducted with the scaled wind farm facility. The simulation and experimental results are compared in terms of power capture, rotor thrust, downstream velocity profiles and turbulence intensity.

Computational Acoustic Beamforming for Noise Source Identification for Small Wind Turbines.

This paper develops a computational acoustic beamforming (CAB) methodology for identification of sources of small wind turbine noise. This methodology is validated using the case of the NACA 0012 airfoil trailing edge noise. For this validation case, the predicted acoustic maps were in excellent conformance with the results of the measurements obtained from the acoustic beamforming experiment. Following this validation study, the CAB methodology was applied to the identification of noise sources generated by a commercial small wind turbine. The simulated acoustic maps revealed that the blade tower interaction and the wind turbine nacelle were the two primary mechanisms for sound generation for this small wind turbine at frequencies between 100 and 630 Hz.

A structural analysis for the scattering and damage accident of wind turbine nacelle covers in Minami Osumi WF

A structural analysis for the scattering and damage accident of wind turbine nacelle covers in Minami Osumi WF

Design of a Modular Extrusion-based Aluminum Monorail System for Highly Accurate Car Positioning

In this paper, the design and experimental evaluation of a sensor platform, including cameras, intended for inspections in remote or difficult-to-access locations; e.g. offshore wind turbine nacelles are presented. The system consists of a sensor system attached to a car that moves on a rail. The main requirements for the design include applicability for high-volume production of rail segments as well as high-accuracy position of the car and the direction sensors face. This accuracy is important for the use of image change detection algorithms. A series of experiments was conducted and the results show that the position errors are just large enough to have an effect on images taken of components one meter away with a 60-degree field of view 1080p camera. However, it is considered realistic that computer vision algorithm can compensate for this.

Durability test of 5MW wind turbine nacelle

Durability test of 5MW wind turbine nacelle

Turbulence upstream of wind turbines: A large-eddy simulation approach to investigate the use of wind lidars

Despite the evolution of wind turbines, the way in which in-situ meteorological information is obtained has not evolved much. Wind vane and cup anemometers, installed at the turbines nacelle, right behind the blades, are still used. This near-blade monitoring does not provide any time to readjust the profile of the wind turbine, and subjects the blades and structure to wind gusts and extreme incoming wind conditions. A solution is to install wind lidar devices on the turbine's nacelle. This technique is currently under development as an alternative to traditional in-situ wind anemometry because it can measure the wind vector at substantial distances upwind. However, most used wind lidar systems are optimized for measuring within a fixed upwind range, but at what upwind distance should they interrogate the atmosphere? This work uses Large Eddy Simulations to create a realistic atmospheric flow to evaluate optimal scanning distances to learn about the incoming turbulence as a function of wind farm configuration and atmospheric stratification. A correlation model, based on a modified truncated normal distribution, has also been developed, which could be implemented within the feed-forward collective pitch control of the turbine, allowing for improved wind turbine readjustments.

Investigation of the incoming wind vector for improved wind turbine yaw-adjustment under different atmospheric and wind farm conditions

Regardless of the evolution of wind energy harvesting, the way in which turbines obtain in-situ meteorological information remains the same - i.e. using traditional wind vanes and cup anemometers installed at the turbine's nacelle, right behind the blades. As a result, misalignment with the mean wind vector is common and energy losses up to 4.6% can be experienced as well as increases in loading and structural fatigue. A solution for the near-blade monitoring is to install wind LIDAR devices on the turbines' nacelle. This technique is currently under development as an alternative to traditional in-situ wind anemometry because it can measure the wind vector at substantial distances upwind. But at what upwind distance should they interrogate the atmosphere? and, what is the optimal average time in which to learn about the incoming flow conditions? This work simulates wind fields approaching isolated wind turbines and wind turbine arrays within large wind farms using Large Eddy Simulations. The goal is to investigate the existence of an optimal upstream scanning distance and average time for wind turbines to measure the incoming wind conditions under different ambient atmospheric conditions. Results reveal no significant differences when measuring the incoming wind vector at different upstream distances, regardless of the atmospheric stratification. Within this framework a 30 min readjustment period is observed to perform the best.

Semi-active control of vibrations of spar type floating offshore wind turbines

A semi-active algorithm for edgewise vibration control of the spar-type floating offshore wind turbine (SFOWT) blades, nacelle and spar platform is developed in this paper. A tuned mass damper (TMD) is placed in each blade, in the nacelle and on the spar to control the vibrations for these components. A Short Time Fourier Transform algorithm is used for semi-active control of the TMDs. The mathematical formulation of the integrated SFOWT-TMDs system is derived by using Euler-Lagrangian equations. The theoretical model derived is a time-varying system considering the aerodynamic properties of the blade, variable mass and stiffness per unit length, gravity, the interactions among the blades, nacelle, spar, mooring system and the TMDs, the hydrodynamic effects, the restoring moment and the buoyancy force. The aerodynamic loads on the nacelle and the spar due to their coupling with the blades are also considered. The effectiveness of the semi-active TMDs is investigated in the numerical examples where the mooring cable tension, rotor speed and the blade stiffness are varying over time. Except for excessively large strokes of the nacelle TMD, the semi-active algorithm is considerably more effective than the passive one in all cases and its effectiveness is restricted by the low-frequency nature of the nacelle and the spar responses.

Correlation and coherence of mesoscale wind speeds over the sea

A large offshore observational dataset from stations across the North and Baltic Seas is used to investigate the planetary boundary‐layer wind characteristics and their coherence, correlation and power spectra. The data from thirteen sites, with pairs of sites at horizontal distances of 4 to 848 km, are analyzed for typical wind turbine nacelle heights. Mean wind characteristics, correlation and coherence are also calculated for analogous wind data from simulations with the Weather Research and Forecasting (WRF) model.Results indicate a general good agreement for the coherence calculated based on measurements and the WRF‐derived time series. By normalizing the frequency axes with the distance and mean wind speed, it can be demonstrated that, even for data with a wide range of distances, the coherence is a function of the frequency, mean wind and distance, which is consistent with earlier studies. However the correlation coefficient as a function of distance calculated from WRF is higher than observed in the measurements. For the power spectra, wind speed and wind speed step change distribution, the results for all sites are quite similar. The land masses strongly influence the individual wind direction distribution at each site. The ability of the WRF model to reproduce the coherence of the measurements demonstrates that its output can be used to estimate the coherence of fluctuations for the integration of offshore energy. The power spectra of WRF time series underestimates the high‐frequency fluctuations. Due to the large number of measurement sites, the results can be used for further plausibility validation for mesoscale model runs over the sea.

Numerical simulation of the interaction between tandem wind turbines

Two model wind turbines operating in tandem are simulated using Tenasi, a node-centered, finite volume unstructured flow solver. The turbine blades are designed using the NREL S826 airfoils. The entire test section of the wind tunnel is simulated since the blockage (based on swept area of the rotor and tower area) was 12%. The simulations included the tunnel walls, wind turbine blades, hubs, nacelles and towers. Detailed experimental data is available for a variety of flow conditions (varying tip-speed-ratios). The results presented here are for tip-speed-ratios of 2.5, 4, and 7 for the rear turbine while the front turbine was always operated at the design tip speed ratio of 6. The tunnel wind speed was 10m/s and the wind turbine RPM was varied to achieve the desired tip-speed-ratios. A DES version of the Menter's SST turbulence model is utilized for the turbulence closure. Turbine performance as well as wake data at various locations is compared to experiment (Blind Test 2 study carried out at NTNU, Norway). Very good agreement is observed for the turbine performance. Good agreement was obtained for velocity fluctuations in the wake region with trends captured very well. Mean velocity predictions agree reasonably well.