Horizontal Axis Wind Turbine Rotor Research Articles

Going beyond BEM with BEM: an insight into dynamic inflow effects on floating wind turbines

Abstract. Blade element momentum (BEM) theory is the backbone of many industry-standard wind turbine aerodynamic models. To be applied to a broader set of engineering problems, BEM models have been extended since their inception and now include several empirical corrections. These models have benefitted from decades of development and refinement and have been extensively used and validated, proving their adequacy in predicting aerodynamic forces of horizontal-axis wind turbine rotors in most scenarios. However, the analysis of floating offshore wind turbines (FOWTs) introduces new sets of challenges, especially if new-generation large and flexible machines are considered. In fact, due to the combined action of wind and waves and their interaction with the turbine structure and control system, these machines are subject to unsteady motion and thus unsteady inflow on the wind turbine's blades, which could put BEM models to the test. Consensus has not been reached on the accuracy limits of BEM in these conditions. This study contributes to the ongoing research on the topic by systematically comparing four different aerodynamic models, ranging from BEM to computational fluid dynamics, in an attempt to shed light on the unsteady aerodynamic phenomena that are at stake in FOWTs and whether BEM is able to model them appropriately. Simulations are performed on the UNAFLOW 1:75 scale rotor during imposed harmonic surge and pitch motion. Experimental results are available for these conditions and are used for baseline validation. The rotor is analyzed in both rated operating conditions and low wind speeds, where unsteady aerodynamic effects are expected to be more pronounced. Results show that BEM, despite its simplicity, can adequately model the aerodynamics of FOWTs in most conditions if augmented with a dynamic inflow model.

Peak Shaving Methods to Reduce Aerodynamic Loads for Pitch-controlled 20 MW Class Horizontal Axis Wind Turbine Rotor

Peak Shaving Methods to Reduce Aerodynamic Loads for Pitch-controlled 20 MW Class Horizontal Axis Wind Turbine Rotor

Reliability analysis of 15MW horizontal axis wind turbine rotor blades using fluid-structure interaction simulation and adaptive kriging model

Over the course of the last four decades, the rotor diameter of Horizontal Axis Wind Turbines (HAWTs) has undergone a substantial increase, expanding from 15 m (30 kW) to an impressive 240 m (15MW), primarily aimed at enhancing their power generation capacity. This growth in blade swept area, however, gives rise to heightened loads, stresses and deflections, imposing more rigorous demands on the structural robustness of these components. To prevent sudden failure and to plan effective inspection, maintenance, and repair activities, it is vital to estimate the reliability of the rotor blades by considering all the forces (aerodynamic and structural dynamics) acting on them over the turbine's lifespan. This research proposes a comprehensive methodology that seamlessly combines fluid-structure interaction (FSI) simulation, Kriging model/algorithm and Adaptive Kriging Monte Carlo Simulation (AKMCS) to assess the reliability of the HAWT rotor blades. Firstly, high-fidelity FSI simulations are performed to investigate the dynamic response of the rotor blade under varying wind conditions. Recognizing the computationally intensive nature and time-consuming aspects of FSI simulations, a judicious approach involves harnessing an economical Kriging model as a surrogate. This surrogate model adeptly predicts blade deflection along its length, utilizing training and testing data derived from FSI simulations. Impressively, the Kriging model predicts blade deflection 400 times faster than the FSI simulations, showcasing its enhanced efficiency. The optimized surrogate model is then used to estimate the flap wise blade tip deflection for one million wind speed samples generated using Weibull distribution. Thereafter, to evaluate the reliability of the blades, statistical modeling using methods such as Monte Carlo Simulation (MCS), AKMCS is performed. The results demonstrate the faster convergence of AKMCS requiring only 21 samples, as opposed to 1 million samples for MCS with minimal reduction in the precision of the estimated probability of failure (Pf) and reliability index (β). Demonstrated on the backdrop of an IEA-15MW offshore reference WT rotor blade, the proposed methodology underscores its potential to be seamlessly incorporated into the creation of WT digital twins, due to its near real-time predictive capabilities for Pf and β assessments.

A BEM theory adaption for inclusion of hub ratio effects in HAWT rotor design and analysis

A large hub ratio in a horizontal axis wind turbine (HAWT) rotor can provide aerodynamic and structural design benefits, but the flow effects are not accounted for in the classical Blade Element Momentum Method (BEMM). Research into the effect of HAWT rotor hub ratio, necessitated development of an adaption to the BEMM, so that rotors with large hub ratios, could be designed to be aerodynamically efficient, and so that the flow effects could be included in performance prediction. Results from the BEMM with large-hub adaption were compared with results from using the classical BEMM and with results from CFD simulation. Two sets of rotors were analysed, one set in a viscous flow regime and the other in a turbulent flow regime. The BEMM with large-hub adaption, was found to provide rotor designs with better performance and provided a more accurate prediction of relative rotor power than the classical BEMM.

Effect of leading-edge protrusion shapes for passive flow control measure on wind turbine blades

In the present study, protrusions in the leading edge of the NACA 4415 airfoil were incorporated as a passive flow control measure on the wind turbine blades. Three airfoil models: unmodified leading-edge (ULE), spherical leading-edge protrusion (SLEP), and triangular leading-edge protrusion (TLEP), were investigated experimentally. Thereafter, CFD investigations were carried out using ANSYS 14.0 simulation tool to observe the flow characteristics around the airfoils. Further, LEP-based passive design was applied on a horizontal axis wind turbine (HAWT) to investigate its performance. An amplitude (A) of 1% of the chord length (C) was considered as the height of protrusion, while a distance of 0.25C was maintained between the protrusions to fabricate the experimental models. The study was performed at a low Reynolds number (Re) of 1.5 × 105 for a wide angle of attack (α) of 0°–20°. The experimental results demonstrate that the SLEP model has a higher lift coefficient at α ≥ 18°, whereas the TLEP model performs poorly when compared with the ULE model. The instantaneous lift coefficient plot indicates that the SLEP model generates a more stable force at a higher angle of attack. The computational analysis reveals that a larger primary circulation (extended till 0.2C) is observed in the ULE model at a post-stall angle of attack (α = 18°), indicating early flow separation. Whereas, in the SLEP and TLEP models, it is extended to 0.70C and 0.54C, respectively, indicating the best flow controlling measures achieved by using the SLEP model. The investigations of HAWT rotors with LEP revealed that SLEP HAWT exhibit 8.2% more power coefficient than ULE HAWT.

GRMWBO: design of a general-purpose repowering model for wind farms via bioinspired optimization

Wind farm optimization requires efficient design of placement models which can assist in identification of deployment locations for higher conversion efficiency. To perform this task, various methods are proposed by researchers, and most of them are applicable for new deployments. Due to limited availability of wind farm sites and cost constraints, it is impractical to replace old equipments. Thus, repowering of wind farms is necessary, and must be planned under existing deployment constraints. Existing repowering methods apply static modelling techniques, which limits their scalability and usability for real-time deployments. To overcome this limitation, a novel general-purpose repowering model via bioinspired optimization is discussed in this text. The model proposes design of a genetic algorithm that considers inflow wind speed, wind direction angle, height of hub, surface roughness, horizontal-axis wind turbine rotor diameter, thrust coefficient, turbine efficiency, air density, and wake expansion rate to estimate location of wind-based generators. These locations are optimized for maximum output power, and minimum deployment costs, which can be estimated for multiple farm areas. This text also proposes various case studies and hypothesis about these deployments, and showcases performance optimizations w.r.t. optimum placement for a given number of turbines. Based on this evaluation, it was observed that the proposed GRMWBO model is capable of improving power efficiency by 18.5%, reduce cost by 8.3%, and reduce number of wind-based generators by 2.9% when compared with various state-of-the-art models. It was also observed that the proposed model showcased consistent performance under different use cases. Thus, making it applicable for a wide variety of real-time deployments.

Aerodynamic Performance of a Horizontal Axis Wind Turbine Operating with Dust—A Computational Study

The main purpose of this study is to develop an understanding of the aerodynamic performance of a horizontal axis wind turbine (HAWT) operating in a dusty environment, with various concentration of dust in the flow domain. The computational analysis was accomplished by the commercial computational fluid dynamics (CFD) code ANSYS Fluent 16.0. Initially, a user-friendly developed application was utilized for the optimum blade geometry special characteristics calculation. The design of the HAWT rotor and meshing of the computational domain follows. The moving reference frame (MRF) model was applied for the rotary motion of the blades, the dust was added in the computational domain by the discrete phase model (DPM) and SST k–ω turbulence model was enabled. The power output of the studied HAWT, operating in several dusty environments, was estimated and compared with the power output of a particular HAWT in clean air. The flow field around the HAWT rotor, including the contours of pressure, particles dissipation rate and erosion rate on both blade sides, are shown. In general, it is concluded that the operation of a HAWT in a dusty environment results in degraded performance, due to the particles deposition on the blades.

Pengaruh Jumlah Sudu dan Pembebanan Terhadap Energi Listrik Yang Dihasilkan OlehTurbin Angin SumbuHorizontal Skala Mikro

<p><em>The needs of electrical energy particularly in Indonesia is very great and continues to increase every year. The development of a micro scale horizontal axis wind turbine can be a solution to solve that. This research has a purpose to find out the influence of number of blades and wind speed variation on electrical energy produced by micro scale horizontal axis wind turbines. The method which was used in this research was experiment method and it was implemented at the Laboratory of Study Program of Mechanical Engineering Education of Sebelas Maret University. The variable that was used in this research was by using blades with airfoil SG6043 with variations of blades number and the giving load in the form of 12v and 24v LED lights. The horizontal axis wind turbine rotor has a diameter of 800 mm and a blade length of 400 mm which is printed with 3D Printing PLA material. The data collection was implemented on the wind speed of 1 m/s to 5 m/s. The results of this research is the wind turbine that used 5 blades produced the highest power of 9.22 Watt at 24v loading and had the highest power performance value of 0.241 at maximum wind speed of 5 m/s. The number of blades and wind speed and loading could affect the electrical power produced by the turbine, the more blades and the higher the wind speed, the greater the power generated by the turbine.</em></p>

Study on the Influence of Low-Level Jet on the Aerodynamic Characteristics of Horizontal Axis Wind Turbine Rotor Based on the Aerodynamics–Controller Interaction Method

Accurate prediction of the aerodynamic characteristics of wind rotors subjected to various wind profiles is of considerable importance in the aerodynamics and structural design of wind turbines. As a very complex atmospheric phenomenon, the impact of a low-level jet (LLJ) on the aerodynamic characteristics of wind rotors is becoming more and more significant with the increase in wind turbine height. Additionally, during calculating the aerodynamic characteristics of the wind rotor, the known wind speed, rotor speed, and blade-pitch angle are generally required. However, when the wind profile is in the LLJ condition, it is difficult to determine the blade-pitch angle and rotor speed. Therefore, in this paper, the blade-element-momentum (BEM) method is exploited by considering the coupling with the generator-torque controller and blade-pitch controller. In order to solve the problem of the unknown rotor speed and blade-pitch angle under the LLJ condition, a C++ code is developed. Then, the influence of the LLJ on the aerodynamic characteristics of the wind rotor is exclusively examined. The research results show that the calculation method can precisely evaluate the rotor speed, blade-pitch angle, and aerodynamic characteristics of the wind rotor. The influence of the LLJ on the aerodynamic loads of the wind rotor is greater than that of the wind shear. When the LLJ is placed inside the rotor swept area, the aerodynamic loads of the blade exhibit two local maximums and local minimums with the variation of the azimuth angle in a rotation period. The closer the LLJ height is to the hub height, the greater the average aerodynamic loads of the wind rotor are, and the smaller the amplitude of aerodynamic loads of the blade is relative to the average value. When the LLJ height is positioned outside the rotor swept area, the change law of the aerodynamic loads of the blade would be similar to that of the wind subjected to a very strong wind shear inflow. This study provides a crucial reference for a more rational assessment of the aerodynamic characteristics of wind turbines under the action of complex wind profiles, as well as revealing the influence of the LLJ on the aerodynamic characteristics of wind turbines.

Improved Stall Delay Model for HAWT Performance Predictions using 3D Navier-Stokes Solver and Actuator Disk Method

The Actuator Disk Method (ADM), in its analytical formulation or combined with Navier-Stokes equations, is widely used for design and/or for aerodynamic analysis of Horizontal Axis Wind Turbines (HAWT). This method has demonstrated its capabilities for performance predictions of HAWT rotors for limited range of wind speeds with lower angles of attack values, i.e. attached flow conditions. However, for typical wind speeds that rotor encounters, under higher angles of attack i.e. stall conditions, such a method cannot describe accurately the flow characteristics around rotor-blades due to severe flow separations coupled with the effects of blades rotation as well as the radial flow over the blades. In this paper, original correction approaches have been proposed for the existing stall delay models to take into account both the blade rotation and the radial flow effects over the rotor blades. For this purpose, the ADM combined with 3D- NavierStokes equations formulation using Large Eddy Simulations (LES) model has been considered to describe the incompressible turbulent flow field around HAWT rotor blades. The resulting mathematical model has been solved using a 3D in-house subroutine developed with OpenFOAM code. The proposed numerical method has been validated against the well recognized reference measurements obtained using the New MEXICO and the NREL Phase VI experimental wind turbines. In comparison with existing stall delay models, the proposed correctionapproaches, especially the radial flow approach, have shown noticeable enhancements on performance predictions of HAWT rotors compared to the experimental measurements. It has been found very low discrepancies to the experimental torque and thrust values, up to 1% and 10% have been recorded respectively.

Performance of a HAWT Rotor with a Modified Blade Configuration

As the world focuses more on clean and green Earth, wind energy plays a significant role. Wind energy is a renewable source of energy that can cope with the ongoing global fossil fuel crisis. The wind energy converters like wind turbines have been studied a lot in terms of design and performance. The current work includes analyzing the output effects of a horizontal axis wind turbine (HAWT) with a modified blade configuration at specific wind speeds. A numerical investigation is carried out using two different numerical software on the chosen airfoil used in blade design validated with the analysis carried out in open-loop wind tunnels. The study is divided into two phases: first, the selected airfoil is tested experimentally and using CFD, and then the findings are compared to those of the University of Illinois Urbana Champaign wind tunnel tests at low Reynolds numbers. The second phase includes the numerical analysis based on the blade element momentum method and non-linear lifting line simulations of modified blade design at high Reynolds number. The numerical results of rotor performance analysis have been compared to existing experimental results. The findings of all numerical investigations agree with those of the experiments. An optimal value of the power coefficient is obtained at a particular tip speed ratio close to the desired value for large wind turbines. For maximum power, this study investigates the optimum pitch angle. The work demonstrated the improved HAWT rotor blade design to produce better aerodynamic lift and thus improve performance.

Design and Performance Analysis of Composite Airfoil Wind Turbine Blade

Abstract
 Small horizontal axis wind turbine rotors with composite airfoil rotor blades were designed and investigated in the present study in order to improve its performance in low wind speed and low Reynolds number (Re) conditions for standalone system. The geometrical and aerodynamic nature of a single airfoil small horizontal axis wind turbine blade curtails efficient energy harnessing of the rotor blade. The use of composite airfoil rotor blade improves energy production but imposes uncertainty in determining an optimal design angle of attack and the off design aerodynamic behaviour of the rotor. This research investigated the effects of two airfoils used at different sections in a composite blade and determined the blade’s optimal design angle of attack for maximum power generation. The wind turbine rotor blades were designed using blade element momentum (BEM) method and modelled by SolidWorks software. The SG6042 and SG6043 airfoils were used for the composite airfoil blades. Five wind turbines were designed with rotor blades of design angles of attack from 3° to 7°. The five wind turbine blades were simulated in computational fluid dynamics to determine the optimal design angle of attack. The composite airfoil wind turbine blade showed improved performance, whereas, the wind power generated ranged from 4966 W to 5258 W and rotor power coefficients ranged from 0.443 to 0.457. The blade with design angle of attack of 6° showed highest performance.
 Keywords: composite airfoil, lift-to-drag ratio, pressure coefficient, Reynolds number, design angle of attack.

Experimental study of a winglet added small wind turbine with a flanged diffuser for domestic applications

Wind power is a reliable form of energy, and increasing the performance of wind turbines has helped to provide an ever-growing portion of the globe with cost-effective power in energy production. However, there are a few limits to the amount of energy that can be extracted using the wind turbine rotor system from an air stream (Wind). The research focuses on the characteristics of a bare and diffuser winglet horizontal axis wind turbine rotor. During the development of the rotor models, the following design parameters of rotor models such as twist, blade angle, chord length, tower height were taken into account. Experiments for rotor models with and without diffuser conditions were performed in the wind tunnel. For different wind speeds in the wind tunnel, rotation rates were measured for each rotor model. For all rotor models, the power coefficient (Cp ) and tip speed (Vc ) were calculated and reported. For the RW2 rotor with winglet and the corresponding power coefficient of 0.433 in the diffuser configuration, a maximum rotation rate of 2460 rpm was observed. The power coefficient for rotor models with winglet configuration (RW1) was increased by 10% and the power coefficient for rotor models with winglet configuration (RW3 & RW4) decreased by 18% in bare configuration as well as the power coefficient for rotor models increased by 4.9% in diffuser configuration.

Experimental investigations of winglet effects on blade geometry of small horizontal axis wind turbine rotors

In this research work, the investigation and optimization of small horizontal axis wind turbine blade at low wind speed is pursued. The experimental blades were developed using the 3D printing additive manufacturing technique. The airfoils E210, NACA2412, S1223, SG6043, E216, NACA4415, SD7080, SD7033, S1210 and MAF were tested at the wind speed of 2-6 m/s. The airfoils and optimum blade geometry were investigated with the aid of the Xfoil software at Reynolds number of 100,000. The initial investigation range included tip speed ratios from 3 to 10, solidity from 0.0431 – 0.1181 and angle of attacks from 2o to 20o. Later on these parameters were varied in MATLAB and Xfoil software for optimization and investigation of the power coefficient, lift coefficient, drag coefficient and lift to drag ratio. The cut-in wind speed of the rotors was 2 and 2.5 m/s with the winglet-equipped blades and without winglets. It was found that the E210, SG6043, E216 NACA4415 and MAF airfoil displayed better performance than the NACA 2412, S1223, SD7080, S1210 & SD7003 for the geometry optimized for the operating conditions and manufacturing method described.

Model free adaptive control of large and flexible wind turbine rotors with controllable flaps

This paper investigates the dynamic load alleviation in large and flexible horizontal axis wind turbine rotors with trailing edge flaps, actuated through a novel proportional-derivative model-free adaptive control (PD-MFAC) system. First an aeroservoelastic wind turbine model is developed, which is the combination of a structural model for the tower and blades represented by geometrically non-linear composite beams, and an aerodynamic model for the rotors using an unsteady strip-theory airfoil model. Then three independent model-free controllers are developed to actuate the trailing-edge flaps mounted on three blades, using the blade root-bending moment (RBM) as control input. Comparison is given by an H-infinity (H∞) reference controller and a Gain-scheduled proportional-integral (GS-PI) controller. Simulation results show that the MFAC flap controller provides more effective load alleviation performance in blade root-bending moment than the H∞ and the GS-PI flap controllers, and it also exhibits marked reductions in blade tip deflection (BTD), in the presence of external disturbances.

A novel linearization approach of chord and twist angle distribution for 10 kW horizontal axis wind turbine

In the present work, the aerodynamic design of a 10 kW horizontal axis wind turbine rotor is performed using both ideal and actual rotor theories. The obtained nonlinear blade profile is optimized in order to enhance the aerodynamic performance and to ease the fabricating complexity. A unique linearization approach is employed to linearize the chord and twist distribution by dividing the congruent line of both ideal and actual models into equal divisions. The points along the identical tangent line are considered as floating new blade roots, whereas the blade tip was kept fixed based on the primary design. The linear profile based on the new value of blade root is described using algebraic equations. The local element torque, capacity factor, and the annual energy production based on the Weibull distribution are adopted to determine and assess the optimal blade profile. Both CFD investigation and the FEA analysis are performed in order to evaluate both primary and optimized blades. The aerodynamic and aeroelastic comparison in terms of power output, thrust force, blade tip deflection, and the equivalent stress distribution of both blade profiles has been done over a wide range of incoming wind speeds. Results show an enhancement in the aerodynamic performance in terms of power coefficient up to (5.9%) compared to the primary blade design. Moreover, the optimized blade has shown less tip deflection by 27.92% than the primary blade at low wind speed.

Dependence of Power Characteristics on Savonius Rotor Segmentation

Savonius rotors are large and heavy because they use drag force for propulsion. This leads to a larger investment in comparison to horizontal axis wind turbine (HAWT) rotors using lift forces. A simple construction of the Savonius rotor is preferred to reduce the production effort. Therefore, it is proposed here to use single-segment rotors of high elongation. Nevertheless, this rotor type must be compared with a multi-segment rotor to prove that the simplification does not deteriorate the effectiveness. The number of segments affects the aerodynamic performance of the rotor, however, the results shown in the literature are inconsistent. The paper presents a new observation that the relation between the effectiveness of single- and multi-segment rotors depends on the wind velocity. A single-segment rotor becomes significantly more effective than a four-segment rotor at low wind speeds. At high wind speeds, the effectiveness of both rotors becomes similar.

Modeling and simulation of forces applied to the horizontal axis wind turbine rotors by the vortex method coupled with the method of the blade element

This article aims to study the forces applied to the rotors of horizontal axis wind turbines. The aerodynamics of a turbine are controlled by the flow around the rotor, or estimate of air charges on the rotor blades under various operating conditions and their relation to the structural dynamics of the rotor are critical for design. One of the major challenges in wind turbine aerodynamics is to predict the forces on the blade as various methods, including blade element moment theory (BEM), the approach that is naturally adapted to the simulation of the aerodynamics of wind turbines and the dynamic and models (CFD) that describes with fidelity the flow around the rotor. In our article we proposed a modeling method and a simulation of the forces applied to the horizontal axis wind rotors turbines using the application of the blade elements method to model the rotor and the vortex method of free wake modeling in order to develop a rotor model, which can be used to study wind farms. This model is intended to speed up the calculation, guaranteeing a good representation of the aerodynamic loads exerted by the wind.

Modeling and simulation of forces applied to the horizontal axis wind turbine rotors by the vortex method coupled with the method of the blade element

This work focuses on the study of the forces applied to the rotors of horizontal axis wind turbines. The aerodynamics of a wind turbine is regulated by the flow around the rotor, where the prediction of air loads on the rotor blades in various operational conditions and its relationship with the structural dynamics of the rotor is crucial for design purposes. One of the most important challenges in the aerodynamics of wind turbines therefore to accurately predict the forces on the blade when the blade and the wake are modeled by different approaches such as the theory of the blade element (BEM) the vortex method and CFD method which involves solving the Navier-Stokes equations. In our article, the model is used for modeling and simulate the forces applied to the rotors of wind turbines horizontal axis use the application of the method of the blade element for modeling the rotor and the vortex method of free wake modeling in order to develop a model of the rotor, which can be used to study wind farms. This model is intended to speed up the calculation, guaranteeing a good representation of aerodynamic loads exerted by the flow of wind.

Data-driven fatigue-oriented MPC applied to wind turbines Individual Pitch Control

Horizontal Axis Wind Turbine (HAWT) rotor is a system whose components are particularly exposed to fatigue damage, due to non-uniform winds and the rotating nature of the rotor. Individual Pitch Control (IPC) can help alleviating the fatigue loads on the rotor blades by rotating the blades independently from each other on their longitudinal axis. However, reducing the blades fatigue damage is often compensated by an increase in pitch activity, damaging the blade pitch actuators. An IPC regulator must thus optimize a trade-off between the fatigue damage of the blades and blade pitch actuators. This paper presents the derivation and implementation of a fatigue-oriented adaptive Model Predictive Control (MPC) IPC regulator using a data-driven fatigue-oriented cost function. This MPC allows to efficiently optimize the IPC fatigue trade-off and significantly reduce the expectancy of an HAWT rotor economic fatigue cost, compared to a finely tuned non-adaptive MPC. The methodology used for the derivation of the presented MPC allows to efficiently reduce an economic fatigue cost, while limiting the sensitivity to controller tuning.