Wind Turbine Rotor Research Articles

Efficiency Improvement Methods of Independent Wind Electric Installation with Programmed Control

Relevance justification of effective automated control method of independent wind electric installation on the basis of voltage feedback and parameters of inductance x1, reduced inductance x′2, phase resistance of starter winding r1, reduced phase resistance of starter winding r′2 is made under different conditions of electric installation operation to minimize the time of phase voltage regulation transient process of wind turbine generator, that promotes quality improvement of self-excitation and reliability indicator improvement of energy supply of the basic control under insufficient information of meteorological and electric power conditions significaltly changing in time. The review of basic ways to control independent wind electric installations which has shown their negative sides is made, that revealed their negative sides like low execution speed and reliability, lack required voltage control quality, idle excitation current distortion leading to voltage sine curve distortion of the asynchronous generator, and providing no relay protection or the automatic switch and automation operating mode control. The differential equation of wind turbine rotor angular speed is composed. Transfer functions of dynamic links for generator phase voltage automatic control of wind turbine taking into account wind speed, rotor winding current, inductance, rotor winding phase resistance, reduced stator winding phase resistance are plotted. The block diagram imitating model is constructed and schedules of transient processes with zero and non-zero delay were plotted providing delay negative effect development decision making on stability of wind turbine generator phase voltage and to establish method of relevant system preparation to external disturbances vanishing above mentioned disadvantage.

Optimization Design Blade Wind Turbine in Enhancing Power Based on Passive Control System

Control power on rotor wind turbine can be carried out by changing blade angle of attack through via pitch control and stall regulated method to produce much power and control power as well as protect wind turbine from high wind to operate in rated power. By using search-based design method to optimize design blade and Blade Element Momentum Theory (BEMT) to analyze aerodynamic performance for stall and pitch control power. Recent work demonstrates that some very significant effect can be achieved by using constant speed pitch control. Comparing of among ordinary blade and design blade of constant speed stall regulated and optimized show that enhancing power is nearly similar while design blade using pitch control give significant effect in enhancing aerodynamic performance of design blade. For average power, design blade constant speed pitch control has average power about 47970,77 Watt and constant speed stall regulated is 43855,41 Watt

Operational modal analysis for damage detection in a rotating wind turbine blade in the presence of measurement noise

The present paper demonstrates the feasibility of detecting and quantifying crack-type damage features in rotating wind turbine blades by Operational Modal Analysis (OMA) under noisy measurement conditions. The excitation of blade vibrations is achieved through the rotationally sampled turbulence spectrum of the inflowing wind field. Accelerations are sampled at 30 locations along the blade. Given the high sensitivity of OMA-reconstructed mode shapes to the presence of noise a six-part methodology has been developed. It is demonstrated that small cracks can be detected reliably down to signal-to-noise ratios (SNR) at the blade tip of 40 dB, well below the SNR values achievable with commercial accelerometers and wind-excited acceleration amplitudes. Calibration curves for crack lengths and center positions have been constructed. The proposed methodology holds the potential for the implementation of robust and low-cost structural health monitoring systems for wind turbines at locations with difficult access, such as in an offshore environment.

An investigation on flow behavior and performance of a wind turbine integrated within a building tunnel

There is a growing interest in the development of sustainable buildings to overcome the degradation of the natural environment by minimizing the carbon footprints of buildings. This goal can be achieved by incorporating renewable energy generation systems into buildings. A promising option is to resort to wind power to energize the urban environment. This work introduces an investigation on the performance of Savonius wind turbine rotor integrated within a building tunnel. The effect of the tunnel width relative to building width is investigated. Moreover, the effect of the tunnel location through a building model is also investigated to attain the best performance and consequently the maximum power generation from the wind. The reasons behind either the degradation or improvement of the wind turbine performance are explored based on the flow behavior including pressure distribution and velocity streamlines through the building tunnel. The numerical results demonstrate the role of vortices evolution on the rotor performance. The numerical simulations presented here are validated by present measurements conducted on the wind turbine installed within a duct and in free stream conditions. The highest performance of the Savonius rotor in terms of power coefficient (Cp) is reached by integrating the rotor within a building tunnel at the best tunnel location far from the center of the building, with a 104% increase in the Cp, as compared to free stream wind turbine.

From shear to veer: theory, statistics, and practical application

Abstract. In the past several years, wind veer – sometimes called “directional shear” – has begun to attract attention due to its effects on wind turbines and their production, particularly as the length of manufactured turbine blades has increased. Meanwhile, applicable meteorological theory has not progressed significantly beyond idealized cases for decades, though veer's effect on the wind speed profile has been recently revisited. On the other hand the shear exponent (α) is commonly used in wind energy for vertical extrapolation of mean wind speeds, as well as being a key parameter for wind turbine load calculations and design standards. In this work we connect the oft-used shear exponent with veer, both theoretically and for practical use. We derive relations for wind veer from the equations of motion, finding the veer to be composed of separate contributions from shear and vertical gradients of crosswind stress. Following from the theoretical derivations, which are neither limited to the surface layer nor constrained by assumptions about mixing length or turbulent diffusivities, we establish simplified relations between the wind veer and shear exponent for practical use in wind energy. We also elucidate the source of commonly observed stress–shear misalignment and its contribution to veer, noting that our new forms allow for such misalignment. The connection between shear and veer is further explored through analysis of one-dimensional (single-column) Reynolds-averaged Navier–Stokes solutions, where we confirm our theoretical derivations as well as the dependence of mean shear and veer on surface roughness and atmospheric boundary layer depth in terms of respective Rossby numbers. Finally we investigate the observed behavior of shear and veer across different sites and flow regimes (including forested, offshore, and hilly terrain cases) over heights corresponding to multi-megawatt wind turbine rotors, also considering the effects of atmospheric stability. From this we find empirical forms for the probability distribution of veer during high-veer (stable) conditions and for the variability in veer conditioned on wind speed. Analyzing observed joint probability distributions of α and veer, we compare the two simplified forms we derived earlier and adapt them to ultimately arrive at more universally applicable equations to predict the mean veer in terms of observed (i.e., conditioned on) shear exponent; lastly, the limitations, applicability, and behavior of these forms are discussed along with their use and further developments for both meteorology and wind energy.

Research on wind-storage coordinated frequency regulation strategy of high permeability wind power connected to regional power grid

With the increasing penetration of wind power in the power system, the proportion of wind turbines in the power system is increasing, replacing the traditional units, which reduces the inertia constant of the system and the reserve capacity of frequency regulation. This paper analyzes several schemes of wind power participating in system frequency regulation, and summarizes a coordinated frequency regulation control strategy of wind power and storage. The main purpose is to make full use of the inertia of the wind turbine rotor to reduce the allocation of energy storage capacity and effectively reduce the energy storage capacity.

Effects of non‐proportionality and tension–compression asymmetry on the fatigue life prediction of equivalent stress criteria

AbstractBiaxial tension/compression–torsion fatigue tests with varying levels of non‐proportionality were performed employing a structural adhesive designed for wind turbine rotor blades. The cycles to failure were found to be independent of the level of non‐proportionality. It is demonstrated that numerical fatigue life predictions via rainflow‐counted equivalent stress histories are not able to replicate these experimental observations and overestimate the fatigue life up to a hundredfold. The tension–compression asymmetry of the adhesive resulted in significant damage prediction differences depending on the stress space representation of the Haigh diagram. If not properly taken care of, the asymmetry will also lead to non‐conservative results. While demonstrated with a short fiber‐reinforced adhesive, the results can be transferred to other materials.

A comparative examination of the aerodynamic performance of various seashell-shaped wind turbines

The seashell-shaped wind turbine (spiral wind turbine SWT), a brand-new form of the horizontal axis wind turbine, is intended for metropolitan use. SWTs have the additional advantage of being installed anywhere without considering their surroundings, as they do not need to be located facing the wind direction. The present work introduces various designs of the rotor of the seashell wind turbine to achieve the greatest performance. Two types of turbine spiral profiles (logarithmic and Archimedean) are investigated with changing the turbine opening angle (θ). Utilizing the turbulence model SST k-ω, the equations of Reynolds-averaged Navier-Stokes (RANS) are solved and hence the power coefficient (CP) is calculated. A comprehensive comparison of the findings for both configurations indicates that the turbine of the Archimedean spiral profile with θ of 60° generates the best performance. The seashell wind turbine with the Archimedean profile at a θ of 60° has a maximum CP = 0.266825 at λ = 2.5. The seashell wind turbine with the Archimedean profile has the best performance than traditional Archimedes wind turbines which were studied previously by other researchers. The maximum percentage increase in the CP of the seashell turbine with the Archimedean profile compared to the conventional Archimedes turbine equals 14.52%.

Stochastic unit commitment to determine frequency response ramp rate including wind turbines with synthetic inertia and virtual synchronous generator

In this paper, the dynamic frequency constraints are derived for power systems incorporating full-converter wind turbines. These wind turbines could be equipped with a virtual inertia by either synthetic inertia control or virtual synchronous generator concept. In the former scheme, deviations in the wind turbines rotor speed remain in synchronism with the system frequency. However, the wind turbines start to restore their rotor speed before the system frequency recovery initiation, in virtual synchronous generator scheme. The restriction on the virtual inertia are determined considering a limit variable on wind turbines rotor speed drop. The frequency response requirements are derived in terms of governor’s base power, ramp rate and reserve power. A linear frequency nadir constraint is also proposed for the synthetic inertia strategy. Then, the constraints are integrated into the stochastic unit commitment to be consistently and economically met over 24-hour period. As such, the contingency size management are coordinated with the virtual inertia provision. The unit commitment results of IEEE 118-bus system including multiple wind farms reveal that the virtual synchronous generator concept can be an optimal solution for future low-inertia grid’s challenges. Finally, accuracy of the unit commitment results is validated through time-domain simulations of the detailed system model.

The permanently rotating wind turbines: a new strategy for reliable power system frequency support under low and no wind conditions

The problem of frequency stability becomes more concerning as the presence of converter-interfaced units increases and conventional generators are suppressed. A decrease in total system inertia, inherently delivered by synchronous generators, results in abrupt frequency changes and jeopardizes power system stability. Therefore, securing sufficient flexible resources with frequency support capability is necessary. The rotational masses of wind turbines (WTs) are a significant and economical source of flexibility in power systems. However, the available kinetic energy (KE) of the WTs’ rotational masses depends on wind conditions and can only be exploited when the wind speed is sufficient for their rotation. When the wind speed is low, the WT is stopped and cannot support the frequency recovery. In this paper, a new concept of WT operation is proposed, which enables the permanent rotation of the WT under low and no wind conditions, making them reliable flexible resources that can continuously provide frequency support. Due to its widespread presence, the doubly-fed induction generator (DFIG) type of machine was considered. The variable-speed WT’s converter management allows rotational speed control, fast power injection, and release of the turbine’s stored KE even when no wind energy is available. The estimated accessible KE in the WT justifies the proposed concept, and the energy consumption due to motoring operation under low and no wind conditions is shown to be acceptable. A case study is performed for the South Banat region in Serbia to demonstrate the presented management concept. Additionally, a dynamic simulation was implemented to illustrate the permanent operation strategy’s impact on frequency stability in a low-inertia system under low and no wind conditions. Besides virtual inertia continuous capability, the proposed concept provides reduced wear of the WT mechanical components due to a lower number of on/off events.

Optimal low voltage ride through of wind turbine doubly fed induction generator based on bonobo optimization algorithm

The large-scale wind energy conversion system (WECS) based on a doubly fed induction generator (DFIG) has gained popularity in recent years because of its various economic and technical merits. The fast integration of WECS with existing power grids has caused negative influence on the stability and reliability of power systems. Grid voltage sags produce a high overcurrent in the DFIG rotor circuit. Such these challenges emphasise the necessity of the low voltage ride through (LVRT) capability of a DFIG for ensuring power grid stability during voltage dips. To deal with these issues simultaneously, this paper aims to obtain the optimal values of injected rotor phase voltage for DFIG and wind turbine pitch angles for all operating wind speeds in order to achieve LVRT capability. Bonobo optimizer (BO) is a new optimization algorithm that is applied to crop the optimum values of injected rotor phase voltage for DFIG and wind turbine pitch angles. These optimal values provide the maximum possible DFIG mechanical power to guarantee rotor and stator currents do not exceed the rated values and also deliver the maximum reactive power for supporting grid voltage during faults. The ideal power curve of a 2.4 MW wind turbine has been estimated to get the allowable maximum wind power for all wind speeds. To validate the results accuracy, the BO results are compared to two other optimization algorithms: particle swarm optimizer and driving training optimizer. Adaptive neuro fuzzy inference system is employed as an adaptive controller for the prediction of the values of rotor voltage and wind turbine pitch angle for any stator voltage dip and any wind speed.

Sliding mesh simulations of a wind turbine rotor with actuator line lattice‐Boltzmann method

AbstractSimulating entire wind farms with an actuator line model requires significant computational effort, especially if one is interested in wake dynamics and wants to resolve the tip vortices. A need to explore unconventional approaches for this kind of simulation emerges. In this work, the actuator line method is implemented within a lattice‐Boltzmann flow solver, combined with a sliding mesh approach. Lattice‐Boltzmann solvers have advantages in terms of performance and low dissipation, while the sliding mesh allows for local refinement of the blade and tip vortices. This methodology is validated on a well‐documented case, the NREL Phase VI rotor, and the local refinement is demonstrated on the NREL 5 MW rotor. Results show good agreement with reference Navier–Stokes simulations. Advantages and limitations of the sliding mesh approach are identified.

Nonlinear inviscid aerodynamics of a wind turbine rotor in surge, sway, and yaw motions using a free-wake panel method

Abstract. We investigate the aerodynamics of a surging, heaving, and yawing wind turbine with numerical simulations based on a free-wake panel method. We focus on the UNAFLOW (UNsteady Aerodynamics of FLOating Wind turbines) case: a surging wind turbine which was modeled experimentally and with various numerical methods. Good agreement with experimental data is observed for amplitude and phase of the thrust with surge motion. We achieve numerical results of a wind turbine wake that accurately reproduce experimentally verified effects of surging motion. We then extend our simulations beyond the frequency range of the UNAFLOW experiments and reach results that do not follow a quasi-steady response for surge. Finally, simulations are done with the turbine in yaw and heave motion, and the impact of the wake motion on the blade thrust is examined. Our work seeks to contribute a different method to the pool of results for the UNAFLOW case while extending the analysis to conditions that have not been simulated before and providing insights into nonlinear aerodynamic effects of wind turbine motion.

Dynamic modeling and vibration analysis of offshore wind turbine rotor system with insulated bearing under inclined shaft current damage

The offshore wind turbine is a device that uses the wind energy on the ocean to generate electricity. The voltage generated by offshore wind turbine can break down the insulated bearing and cause inclined shaft current damage. To explore the dynamic characteristics and influencing factors of offshore wind turbine rotor system, a dynamic model of offshore wind turbine rotor system is proposed. The insulating coating, inclined shaft current damage and contact characteristics are considered in the model. Through numerical simulation, the mapping relationship between vibration response and damage length is studied, the influence of the interaction between inclination angle and radial clearance on vibration response is analyzed, and the influence of the mass of insulating coating and speed on vibration response is discussed. The practicability of the model is proved by the experiment of physical prototype. The results show that, as the length of the shaft current damage increases from 10 × 10−5 m to 50 × 10−5 m, the strength of the vibration response increases. The coupling of the inclination angle of the shaft current damage and the radial clearance jointly promotes the enhancement of the vibration response. The enhancement effect of radial clearance is more significant than that of inclination angle. The increase of speed worsens the state of operation, and the state transitions from stable quasi-period to chaos.

A new fault detection strategy for wind turbine rotor imbalance based on multi-condition vibration signal analysis

Aiming at the problem that it is difficult to accurately detect the position and magnitude of pitch angle deviation (PAD) fault of wind turbine (WT) in operation at the same time, this paper proposes a novel multi-parameter synergy mechanism based on a double threshold judgment method combined with power spectral density analysis. First, the influence of different PADs of a single blade on the time domain information of WT parameters under different turbulent wind speeds is discussed. Second, according to the changing rule of three blade parameters caused by the single blade PAD, the double threshold judgment method is introduced to determine the faulty blade and the direction of PAD. Third, this paper put forward the concept of characteristic frequency power ratio. Based on the characteristic frequency of the power spectrum, a method is proposed to determine the magnitude of PAD. Finally, a complete set of fault detection and identification flow for single blade PAD was established. This detection strategy is more accurate and faster than the traditional methods and does not need to add additional data acquisition equipment in the wind power generation system.

WITHDRAWN: Control on wind turbine rotor aerodynamics and platform motions employing trailing edge flaps

This article has been withdrawn at the request of the author. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/policies/article-withdrawal.

Blade mass imbalance identification and estimation for three-bladed wind turbine rotor based on modal analysis

Early detection of rotor imbalance is one promising approach to address wind turbine durability. This work proposes a novel blade mass imbalance identification and estimation method for the wind turbine rotor. The method is capable of identifying the presence of a wind turbine rotor mass imbalance. In addition, if a mass imbalance exists in the wind turbine rotor, this method can identify which blade is imbalanced, and then quantify the imbalance severity. The remediation to balance the wind turbine rotor is also provided. The advantages of this method include that only a handful of data is required as input variables (which are the frequencies and modes shapes of all first-order modes) and the method can be applied to a stationary (non-rotating) rotor prior to the first operation. The decision-making process of this method is fast and reliable. The performance of the method is illustrated with the help of both numerical simulation and experimental tests. Model to test correlation and direct blade physical measurements are also conducted to validate the ability of the method to both identify mass imbalance and quantify the degree of mass imbalance. This method was demonstrated to be a high-fidelity tool for identifying the imbalance of the wind turbine rotor and it is also applicable to the wind turbines operating in the field. In addition, this method also shows strong potential to be extended to other wind turbine configurations and even other rotating machinery such as propellors and symmetric, repeated structures.

Computational investigation of NREL Phase-VI rotor: Validation of test sequence-S measurements

A CFD-based assessment and validation of the NREL Phase-VI Sequence-S rotor at seven wind speeds presented here. The ability of a three-dimensional, unstructured, unsteady RANS solver in successfully predicting the wind flow interactions with a rotating, twisted and tapered rotor is described. The uRANS equations were coupled with SST κ-ω turbulence model and a correlation-based Gamma-Theta transition model. The simulations were performed in ANSYS CFX using both Single Reference Frame (SRF) and Multiple Reference Frame (MRF) modelling approaches. A good agreement with measurements is observed at six of seven wind speeds when comparing the integral quantities, the spanwise and chordwise distributions. The only exception is the 10 m/s wind speed case, attributed to the onset of a massive leading edge stall around the mid-span region. It is successfully demonstrated here how uRANS-based CFD computations can be effectively employed in the study of wind turbine rotor aerodynamics.

Evolutionary optimization of a Savonius rotor with sandeel-inspired blades

A possible way to capture the kinetic energy available in the wind and then convert it into a useful form of energy is to use wind turbines. Out of many kinds of wind turbines, a lot of in-depth studies have been conducted to improve the performance of the drag-based vertical-axis wind turbine called Savonius rotor. This kind of vertical-axis wind turbine usually suffers from poor energy conversion efficiency, particularly for its conventional shape (thin half-cylinders). In the current work, a bionic blade shape of the Savonius-type wind turbine rotor inspired by sandeels (also called sandlances) is proposed, combined with an optimization step in order to maximize performance. Sandeels are slim elongated fish that often swim in vast shoals. The bionic blade is described by two principal geometrical parameters, both divided by the blade length (d); the maximum blade camber (fmax) and its location (Xfmax). The optimization relies on evolutionary algorithms to maximize the average power coefficient of the Savonius rotor with sandeel-inspired blades when varying the two design parameters. A total of 128 individuals have been evaluated numerically using a series of two-dimensional transient simulations with the software Star-CCM+. In comparison to the conventional rotor with two arc-type semi-circular blades, the optimal design with sandeel-inspired blades exhibits a considerable increase in turbine efficiency of up to 9.21% at the design tip speed ratio (λ = 0.8). Investigating the performance over the entire operating range results in a maximum power coefficient of 0.255 by the optimal rotor, leading to a gain of about 10.58% with respect to the standard rotor at λ=1.

Assessment of Blade Element Momentum Theory-based engineering models for wind turbine rotors under uniform steady inflow

Blade Element Momentum Theory (BEMT) -based approaches provide 15%–20% inaccurate load predictions under uniform steady inflow. Inaccuracies were related to unclear aerodynamic mechanisms causing the Prandtl Tip-Root Loss (TRL) correction to fail at high Tip-Speed Ratio (TSR) and the ambiguous drag coefficient treatment under Stall Delay (SD). With this study, we provide an in-depth flow analysis to explain what physical mechanisms are poorly captured in TRL and SD corrections and offer a potential solution for the improvement of the Prandtl model. Corrections are assessed by comparison with RANS CFD simulations of the NREL 5MW rotor at its design TSR, TSR 4, and TSR 10. The Prandtl tip-loss correction provides 5%–15% higher loading than CFD at TSR 10. The reason is a lower (0.5°) downwash angle of attack, providing a 5%–10% lift coefficient overestimation. We recommend employing the tip-loss correction of Zhong, as it considers the lift coefficient reduction due to the tip-vortex downwash. The investigated Eggers SD correction predicts an incorrect drag coefficient at TSR 4, while a better agreement is found for the lift coefficient. We conclude that only the latter requires a correction for SD in the inboard blade.