Aerodynamic Imbalance Research Articles

Wind turbine condition monitoring dataset of Fraunhofer LBF

Fraunhofer wind turbine dataset contains monitoring data from a 750 W wind turbine, including accelerometers and tachometer, to capture structural response, bearing vibrations and rotational velocity. Additionally, temperatures, wind speed and wind direction have been measured, while weather conditions have been acquired from selected sources. Various damage scenarios, including mass imbalance, and aerodynamic imbalance as well as damages on bearings’ outer race, inner race and roller element have been implemented. The availability of time series data makes the dataset well suited for both machine learning and signal processing-based condition monitoring applications. The availability of heterogeneous sensors has created a dataset particularly suited for information fusion, data fusion, multi-sensor approaches, and holistic monitoring. Experiments were conducted in real-world conditions outside of a controlled laboratory environment, thereby introducing challenges such as variable rotor speed, noise, overloads, and other environmental factors. Consequently, the dataset is qualified for tasks involving uncertainty quantification and signal pre-processing. This document will detail the test equipment, experimental procedures, simulated damage cases and measurement parameters.

Effects of fluctuating velocity on dynamic stall of vertical axis wind turbine airfoil

In contrast to the classical dynamic stall with steady velocity, the dynamic stall phenomenon observed in vertical axis wind turbines encompasses not only periodic variations in the angle of attack but also periodic fluctuation in velocity. Therefore, this study performs a research to deepen understanding of the dynamic stall characteristics of an airfoil used in a vertical axis wind turbine when subjected to fluctuating velocities. The formation of the leading-edge vortex is brought forward for a larger resultant velocity and postponed for a smaller one, according to the comparing the dynamic stall characteristics under different fluctuating velocities and phase angles. Meanwhile, the convection and dissipation of the leading-edge vortex is also diminished as a result of the smaller resultant velocity. As a result, the aerodynamic loads, particularly the drag coefficient, present a nonsymmetrical form. Finally, the tangential force coefficient of an airfoil under fluctuating velocity is shown to have a larger peak in the upwind region and smaller peak in the downwind region, indicating that the blade of a vertical axis wind turbine would suffer more obviously aerodynamic imbalance under a lower tip speed ratio condition.

Automatic detection and correction of aerodynamic imbalances: a noise-based approach

This paper proposes the use of noise emissions to identify and rectify aerodynamic imbalances. The approach leverages the fact that a pitch imbalance changes the angle of attack at the blade sections, which in turn results in a change in noise emissions. Simulations performed on a 3.35 MW wind turbine show that aerodynamic imbalances significantly affect the Overall Sound Pressure Level at the 1P rotor frequency, more so than mass imbalances, and this effect is furthermore dependent on the microphone placement around the turbine.The rebalancing algorithm is tested through simulations in various scenarios, including both single and multiple concurrent blade imbalances, under different wind speeds and turbulence conditions. The algorithm successfully minimizes aerodynamic imbalances in most cases.

Research on the Effect of Aerodynamic Imbalance on Fatigue Performance of a Wind Turbine Foundation with Embedded Steel Ring

Research on the Effect of Aerodynamic Imbalance on Fatigue Performance of a Wind Turbine Foundation with Embedded Steel Ring

Effects of the yaw error and the fault conditions on the dynamic characteristics of the 15 MW offshore semi-submersible wind turbine

The floating offshore wind turbines (FOWTs) have a higher failure rate compared to onshore wind turbines, which could lead to aerodynamic imbalance on the floating systems. In addition, yaw error presents an inevitable challenge for FOWTs. This study aims to investigate the effects of the yaw error and the fault conditions on the dynamic properties of the IEA 15 MW semi-submersible FOWT using OpenFAST. The fault conditions involve blade seize without shutdown, blade seize with shutdown and grid loss. The platform motions and structure loads under different yaw errors (−20°, −8°, 0°, 8°, 20°) for different fault conditions were investigated. The dynamic response resulting from the fault was compared with the normal condition. Moreover, the optimal yaw angle under fault conditions was investigated in this paper. The results revealed that the fault shutdown conditions significantly impact the motions and loads of the wind turbine, with substantial reverse tower top and base bending moments. The yaw error, conversely, has less effect on the motions of the wind turbine, but can ameliorate the transient effect in the fault shutdown conditions. Additionally, it is recommended to operate the wind turbine at a yaw angle of 25–30° for wind speeds greater than 12 m/s.

Methodology for assessing and reducing the aerodynamic imbalance of the impellers of GTE fans

The reasons for the occurrence of increased vibration of the engine rotor due to aerodynamic imbalance of the fan of the first stage of the impeller are determined. A method for estimating the aerodynamic imbalance of the gas turbine engine fan is proposed, taking into account the influence of the following factors: geometric errors in the manufacture of blade airfoils and their positioning in the disk; deformation of the blade airfoil during the assembly of the impeller, as well as the factors of the working process occurring in the impeller. The use of the technique makes it possible to evaluate the aerodynamic imbalance of the impeller at the stage of its balancing and significantly reduce the amount of aerodynamic imbalance by determining the parameters for removing a layer of material or adding corrective masses. The influence of geometric errors of the blades on the value of the aerodynamic imbalance of the impeller was analyzed. Based on the results of the research, the type of dependence of unbalanced gas forces on the influence of technological and operational factors of the impeller under consideration was determined.

Detection of magnitude and position of rotor aerodynamic imbalance of wind turbines using Convolutional Neural Network

Rotor imbalances present a serious problem for wind turbines. In particular, for offshore wind turbines, aerodynamic imbalance can have a severe impact because of the large rotor size. In this study, the impact of the aerodynamic imbalance is investigated. A novel framework for detecting aerodynamic imbalance is proposed. Firstly, a model of a 3MW direct-driven wind turbine was developed. The signals were acquired to test and verify the impact of aerodynamic imbalance. Secondly, a method based on optimized maximum correlated kurtosis deconvolution was proposed for the primary detection. The intrinsic mode functions of nacelle vibration were adopted as the input variable. The weak unbalanced signals could be discerned. Moreover, the azimuth of rotor allows the unbalanced blades to be obtained. Thirdly, a convolutional neural network with a new structure was used to determine the magnitudes of aerodynamic imbalances. The first layer of the convolutional neural network is sufficiently wide for improving feature extraction, it could make nacelle acceleration as the input. This structure exhibits accuracy and robustness satisfactorily. Finally, the framework was demonstrated in a high-fidelity simulation environment. Different scenarios of aerodynamic imbalance were tested, the results demonstrate the satisfactory performance of the proposed framework.

Allowable Pitch Angle of Aerodynamic Imbalance Due to Individual Pitch Movement for Ultimate Loads on Offshore Wind Turbine Using Artificial Neural Network

This study aims to calculate the ultimate loads through integrated load analysis under aerodynamic imbalance by individual pitch movement of offshore wind turbines, and based on this, to identify the allowable region of the individual pitch angle of the blade. For this, 5 MW offshore wind turbines were modeled using GH-BladedTM based on jacket type substructure data of the NREL-5 MW generic model and Upwind reports. For integrated load analysis, wind speeds were selected: 11 m/s, 14 m/s, 17 m/s, 20 m/s, 22 m/s, and 24 m/s. Ultimate load analysis was performed through the fixed pitch control mode with the individual pitch angles at an interval of 2°, ranging from 0° to 30°. Analysis was performed for the collective pitch control under the same environmental conditions as IPC. Through the comparison of loads at hub for CPC and the individual pitch movement states calculated through integrated load analysis, we identified the allowable pitch angle region where the ultimate loads of the individual pitch movement conditions were less than those of the CPC conditions. Furthermore, pattern analysis was performed using the artificial neural network for numerical modeling of the allowable pitch angle region. The results confirmed a high success rate of over 99%. Based on these results, this study suggested a new model according to the wind speed for the allowable pitch angle region.

Wind Turbine Rotor aerodynamic imbalance detection using CNN

This paper investigates the use of convolutional neural networks (CNN) to automatically detect aerodynamic imbalances in horizontal axis wind turbines (WTs). The database is assembled with low-frequency acquisition rates, similar to those obtained using supervisory control and data acquisition (SCADA) systems. The methodology considers imbalances caused by pitch errors only, which might occur due to installation faults or pitch control errors. The measured raw data is initially processed using traditional statistical techniques. Next, the Gramian Angular Field (GAF) method is used to transform the statistical data into images, and then, a CNN is trained to identify aerodynamic rotor imbalance. The proposed methodology is evaluated under numerical simulations of a 1.5 MW wind turbine, and the accuracy and feasibility of the method are demonstrated. The paper demonstrates that it is possible to detect an aerodynamic imbalance in wind turbine rotors from statistics descriptors of nacelle IMU translational accelerations and wind speeds, considering a sampling frequency of above 0.05 Hz, and using an artificial intelligence technique.

Impact of pitch actuator fault on 10-MW semi-submersible floating wind turbine

The pitch actuator of the offshore wind turbine has a high failure rate, and this fault will lead to aerodynamic imbalance on the floating system, especially when the 10 MW wind turbine is applied. In this paper, the impact of actuator faults on the floating platform motion and turbine structure is investigated. The 10-MW OO-Star semi-submersible platform is used as the reference structure. The fault discussed in this study involved one blade seizing, followed by an emergency shutdown. Coupled non-linear aero-hydro-servo-elastic simulations were carried out in the time domain using OpenFAST. The platform motions and structural loads caused by the fault were compared with the normal operating conditions. The effects of the pitch rate at the initial fault on the loads of the critical components are presented. The results revealed that imbalanced loads due to blade seizing can lead to particularly large excitations of the dynamic responses of the wind turbine. The maximum lateral nacelle acceleration is increased by 27.9%. In addition, the parametric study on the effects of the pitch rate for feathering blade was carried out. It was found that the pitch rate of 8 deg/s is favorable to alleviate the structural loads.

Methodology for assessing the aerodynamic imbalance of GTE impellers

Increased vibration during testing and operation of gas turbine engines may be caused by aerodynamic imbalance. As usual, aerodynamic imbalance is eliminated on stands simulating the operating conditions of the impellers. Existing stands have a high cost of testing or do not allow to make allowances for all the factors during the operation of the impellers. A review of models and techniques has shown the importance of considering operating parameters when calculating aerodynamic imbalance. The paper provides a methodology for calculating the aerodynamic imbalance of the impeller. The methodology is based on the use of finite element modeling (FEM). The proposed method for assessing the aerodynamic imbalance of the impellers makes it possible to take into account the rotational speed, the actual geometry of the blades based on the measurement results, as well as the assembly conditions and the operating conditions of the impeller. The technique was used through the example of a specially designed and manufactured impeller with geometric deflections. Theoretical and experimental studies have been carried out. The discrepancy between theoretical and experimental data did not exceed 15.5%. The developed model can be used at enterprises that manufacture gas turbine engines, gas compressor units, steam turbine plants and wind power plants.

Effect of individual blade pitch angle misalignment on the remaining useful life of wind turbines

Abstract. An empirical data set of laser-optical pitch angle misalignment measurements on wind turbines was analyzed, and showed that 38 % of the turbines have been operating outside the accepted aerodynamic imbalance range. This imbalance results from deviations between the working pitch angle and the design angle set point. Several studies have focused on the consequences of this imbalance for the annual energy production (AEP) loss and mention a possible decrease in fatigue budget, i.e., remaining useful life (RUL). This research, however, quantifies the effect of the individual blade pitch angle misalignment and the resulting aerodynamic imbalance on the RUL of a wind turbine. To this end, several imbalance scenarios were derived from the empirical data representing various individual pitch misalignment configurations of the three blades. As the use case, a commercial 1.5 MW turbine was investigated, which provided a good representation of the sites and the turbine types in the empirical data set. Aeroelastic load simulations were conducted to determine the RUL of the turbine components. It was found that the RUL decreased in most scenarios, while the non-rotating wind turbine components were affected most by an aerodynamic imbalance.

Theoretical study into the aerodynamic imbalance of a propeller blade and the correcting masses to balance it

This paper reports the theoretically investigated aerodynamic imbalance of the propeller blade, as well as correcting masses for balancing it. It has been established that the aerodynamic forces acting on the propeller blade can be balanced by the adjustment of masses. This is also true for the case of compressed air (gas) provided that the blades are streamlined by laminar flow. That makes it possible to use rotor balancing methods to study the aerodynamic forces acting on the propeller blade. The rotating blade mainly generates torque aerodynamic imbalance due to a lift force. A much smaller static component of the aerodynamic imbalance is formed by the drag force acting on the blade. The correcting mass located in the propeller plane balances both static and torque components of the aerodynamic imbalance in its correction plane. A second correcting mass (for example, on the electric motor shank) balances the torque component of aerodynamic imbalance in its correction plane. The calculations are simplified under the assumption that the equilibrium of aerodynamic forces is perpendicular to the chord of the blade. For approximate calculations, one can use information about the approximate location of the pressure center. The aerodynamic forces acting on the blade can be determined on the basis of the correcting masses that balance them. The accuracy in determining the aerodynamic forces could be improved by measuring a lift force. The computational experiment has confirmed the theoretical results formulated above. The experiment further proves the possibility of applying the devised theory for propellers whose rotation speed changes with a change in the angles of blade installation. The findings reported here could be used both for devising methods of propeller balancing and for constructing methods to study the aerodynamic forces acting on the blade.

Research on the Fault Characteristic of Wind Turbine Generator System Considering the Spatiotemporal Distribution of the Actual Wind Speed

A reliable fault monitoring system is one of the conditions that must be considered in the design of large wind farms today. The most important factor for the fault monitoring should be the accurate diagnosis criteria with sensitive fault characteristics. Most of the current fault diagnosis criteria are obtained based on the average wind speed at the center of the hub which is not in accord with the actual wind condition in nature. So, this paper utilizes an equivalent wind speed (EWS), which can describe the actual wind speed spatiotemporal distribution on the rotor disk area considering the effects of wind shear and tower shadow, to analyze the common mechanical and electrical faults again. Firstly, the EWS model applicable to the 3-blade wind turbines is introduced; then the new fault characteristics of the wind turbine rotor aerodynamic imbalance and the stator winding asymmetry are theoretically analyzed based on the EWS model; finally, the simulation platform is built in Matlab/Simulink for comparison and the simulation result is well consistent with the theory analysis. The aim of this research is to find more accurate fault characteristics and help promoting the healthy development of wind power industry.

A Comparative Study on Primary Bearing Rating Life of a 5-MW Two-Blade Wind Turbine System Based on Two Different Control Domains

Recently, the importance of individual pitch control (IPC) capability in wind turbine systems has been emphasized to achieve the desired power performance and mitigate the aerodynamic imbalance load for the mechanical integrity. Compared to collective pitch control (CPC), which assigns identical pitch angles for all employed blades, IPC is capable of generating other various sets of pitch angles to manipulate the aerodynamic load. Thus, the mechanical elements of wind turbine systems may take advantages from this variation, which allows wind turbines to have lighter designs and longer lifetimes. One of the essential mechanical components in the wind turbine is a primary bearing supporting the blades–rotor–shaft unit, which has not been fully investigated yet among the structural elements in the wind turbine system. In this regard, this research focuses on predicting the bearing life span of a NACA64-A17 two-blade 5-MW wind turbine system for the domains of allowable individual pitch angles by IPC. In particular, under the effect of various wind speeds, a bearing life span was determined based on the average value of load cases—satisfying both appropriate power level and the allowable domain of pitch control angles, which were possibly conveyed by IPC—and the result was compared with the bearing life predicted based on the domain of pitch angles, as generated by the CPC strategy. Consequently, in the ranges of high wind speeds, it was found that the average applied load to the bearing is reduced under the domain of the IPC-based pitch angle, resulting in possibly increasing the life span of the bearing. With the presented results, it is hoped that this work will provide important insights for those that majorly concern designing the primary bearing of the IPC-based wind turbine system.

Wind tunnel setup for experimental validation of wind turbine control concepts under tailor-made reproducible wind conditions

To speed up validation and prototyping of novel control and design concepts in wind energy, wind tunnel experiments should be used in synergy with numerical simulations and field experiments. The paper presents a wind tunnel setup consisting of a scaled wind turbine model MoWiTO and an active grid for generation of tailor-made and reproducible inflow conditions. To demonstrate that the presented experimental setup is suitable for fast validation of advanced control concepts, several control algorithms have been implemented and validated in various inflow conditions, such as turbulent and sheared inflows, and wind gusts. The tested control algorithms include the baseline collective pitch and torque control, individual pitch control for load reduction, and a control algorithms for compensation of static aerodynamic imbalances. All control algorithms resulted in an expected behaviour of the model wind turbine, thus emphasizing that the presented experimental setup can be used for fast and inexpensive testing of control concepts.

Vibration control in wind turbines to achieve desired system-level performance under single and multiple hazard loadings

The increased demand in energy and the need for sustainable and renewable sources of electricity in hazardous environments with significantly growing population yields the installation of more wind turbines in these areas. In addition, the technological development in material and construction methods has led to the building of taller and more flexible turbines, with inherent low structural damping. Installing modern wind turbines in offshore harsh environments or seismic prone areas can cause an increment in the probability of failure due to excessive vibrations. The current study evaluates the performance of onshore and offshore wind turbines under multihazard loads, including wind, wave, earthquake, and mass and aerodynamic imbalances for both parked and operating conditions. The Lagrangian approach is employed to model the wind turbine considering the blade/tower coupling. In order to lessen the vibrations induced by multihazard loads, external smart dampers are used and a novel energy-based probabilistic approach is employed to tune the semiactive controllers. The results show the effectiveness of employing an analytical approach for the design of semiactive controllers in vibration mitigation of a wind turbine subjected to multiple hazards.

Patterns in change and balancing of aerodynamic imbalance of the low­pressure axial fan impeller

We have studied patterns in the change and balancing of aerodynamic imbalance of the impeller for the axial fan of type VO-06-300 (Ukraine). We have found the aerodynamic imbalance of the impeller caused by mounting one blade: – at a different angle of attack; – with a violation in the step uniformity; – not perpendicularly to the longitudinal axis of the impeller; – with all three of the above-mentioned errors present at once. We have estimated a change in the aerodynamic imbalance due to change in air density. We estimated the influence of air temperature, altitude above sea level, atmospheric pressure, on air density and aerodynamic imbalance. It was established that a different angle of attack and a violation of the perpendicularity give rise to the dynamic imbalance in which the moment component is an order of magnitude larger than the static component. A violation of the step uniformity gives rise only to the static component, which is in the plane of the impeller. Among the errors considered, the most undesirable one relates to mounting a blade at a different angle of attack. At such an error, aerodynamic imbalance is 6‒8 times larger than that due to other errors. A ±4-degree change in the angle of attack of a single blade in the impeller can degrade the accuracy of balancing of the impeller to the accuracy class G 6.3 at a frequency of 1,500 rpm, or G 16 ‒ at 3,000 rpm. It was established that the ordinary and aerodynamic imbalances can be balanced at the same time. It is appropriate to carry out dynamic balancing in two correction planes. It is possible to conduct balancing by rotor mass correction or using passive auto-balancers. A specific example is used to demonstrate the procedure for taking into consideration the aerodynamic imbalance in differential equations of motion of the axial fan. In accordance with the procedure, the aerodynamic imbalance components are added to the respective components of the ordinary imbalance. The results obtained are applicable when designing and manufacturing low-pressure axial fans. Employing them would improve vibration characteristics of the specified fans.

Monitoring rotor aerodynamic and mass imbalances through a self-balancing control

A typical concern in rotating systems is related to rotor imbalances, which result typically from pitch misalignment and unbalanced mass distribution. A novel control for simultaneously targeting mass and pitch imbalances on the rotor is presented. Additionally, a novel detection strategy is developed in order to detect the imbalance source out of the behavior of the control action. More in depth, since the control will generate an artificial aerodynamic imbalance which compensates the pre-existent aerodynamic and inertial ones, one can find and interpret the fingerprint of the imbalance source in the behavior of the balancing controller. A clear advantage of this approach is that the imbalance detection is performed while the control keeps the machine working within its operating limits reducing the down-time and unscheduled maintenance actions.

Equalizing Aerodynamic Blade Loads Through Individual Pitch Control Via Multiblade Multilag Transformation

Control algorithms for rotor load mitigation are today generally adopted by industry. Most of them are based on the Coleman transformation, which is easy to implement and bears satisfactory results when the rotor is balanced. A multitude of causes, e.g., blade erosion, dirt, and especially pitch misalignment, may create significant imbalances. This gives birth to undesirable vibrations and reduced control performance in terms of load mitigation. In this paper, an alternative transformation is introduced, able to detect and quantify the rotor load harmonics due to aerodynamic imbalance. Next, a control algorithm, capable of targeting rotor imbalance itself and simultaneously lowering rotor loads, is presented. The effectiveness of the proposed solution is confirmed through simulations in virtual environment.