Blade Mass Research Articles

Design approaches of performance-scaled rotor for wave basin model tests of floating wind turbines

The Froude scaling law is usually utilized in the wave basin model tests of Floating Wind Turbines (FWTs). However, the Froude-Scaled Rotor (FSR) cannot generate desired aerodynamic loads due to the Reynolds-Number Scaling Effect (RNSE). To mitigate the adverse effects of RNSE, two approaches are proposed to design Performance-Scaled Rotors (PSRs) in this paper. Taking DTU 10 MW baseline wind turbine as an example, the SD2030 airfoil is selected to replace the original FFA-W3-xx airfoils. Maximum Lift Tracking (MLT) and Load Distribution Matching (LDM) algorithms are proposed to assign the chord lengths and twist angles. Herein, MLT leads all airfoils to operate at the optimal angle of attack that corresponds to the maximum lift coefficient and afterwards increasing the chord lengths. LDM simultaneously adjusts the chord length and twist angle, aiming to match the span-wise distribution of normal force at the design point. Results show that both approaches can generate desired rotor thrusts in a range of tip speed ratios, which seems to outperform prior PSRs in the existing publications. The blade mass and inertia can be preserved with careful manufacturing procedures. The redesigned PSRs are helpful to improve the accuracy and reliability of FWT model tests in the wave basin.

Multi-objective aerodynamic and structural optimization of a wind turbine blade using a novel adaptive game method

ABSTRACT In this study, an integrated structural and aerodynamic optimization of a wind turbine blade is performed. A parameterized finite element model of a blade is first presented based on its aerodynamic shape and structural design. Next, a multi-objective optimization model with 27 design variables and complex constraints is established based on annual energy production and blade mass. A novel adaptive win–stay, lose–shift (WSLS) game method is proposed to obtain an integrated optimal solution. In this method, aerodynamic and structural targets are regarded as two game players with profit interaction and conflict. Notable features of this method include adaptive adjustment of a game player’s strategy space and behavioural switching between competitive and cooperative modes according to game rules. An engineering blade example is presented and all goals show improvements over the initial solutions. A comparison and analysis of the results demonstrate proof of the principles of this method.

Sensitivity analysis of the effect of wind characteristics and turbine properties on wind turbine loads

Abstract. Proper wind turbine design relies on the ability to accurately predict ultimate and fatigue loads of turbines. The load analysis process requires precise knowledge of the expected wind-inflow conditions as well as turbine structural and aerodynamic properties. However, uncertainty in most parameters is inevitable. It is therefore important to understand the impact such uncertainties have on the resulting loads. The goal of this work is to assess which input parameters have the greatest influence on turbine power, fatigue loads, and ultimate loads during normal turbine operation. An elementary effects sensitivity analysis is performed to identify the most sensitive parameters. Separate case studies are performed on (1) wind-inflow conditions and (2) turbine structural and aerodynamic properties, both cases using the National Renewable Energy Laboratory 5 MW baseline wind turbine. The Veers model was used to generate synthetic International Electrotechnical Commission (IEC) Kaimal turbulence spectrum inflow. The focus is on individual parameter sensitivity, though interactions between parameters are considered. The results of this work show that for wind-inflow conditions, turbulence in the primary wind direction and shear are the most sensitive parameters for turbine loads, which is expected. Secondary parameters of importance are identified as veer, u-direction integral length, and u components of the IEC coherence model, as well as the exponent. For the turbine properties, the most sensitive parameters are yaw misalignment and outboard lift coefficient distribution; secondary parameters of importance are inboard lift distribution, blade-twist distribution, and blade mass imbalance. This information can be used to help establish uncertainty bars around the predictions of engineering models during validation efforts, and provide insight to probabilistic design methods and site-suitability analyses.

Optimal structural design of biplane wind turbine blades

Biplane wind turbine blades have been shown to have improved structural performance, aerodynamic performance, and reduced aerodynamic loads compared to conventional blade designs. Here, the impact of these factors on blade mass is quantified for the first time. The objectives of this work are to quantify the mass of biplane wind turbine blades which have been designed for realistic loads, and to understand the mass-driving constraints for such blades. A numerical optimization approach is used to design the internal structure of biplane wind turbine blades, minimizing blade mass subject to a number of design requirements which are imposed as constraints. The mass reductions are significant, showing that the optimal biplane blades are more than 45% lighter than a similarly-optimized monoplane blade. This is primarily due to the improved resistance to flapwise deflection when compared to the monoplane blades, which allows for considerably less spar cap material to be used in the biplanes. Biplane blades are also shown to have improved resistance to edgewise fatigue damage, requiring less trailing edge reinforcement. Given such large mass reductions, some criticality is required, and the limitations of the present approach are discussed. The results of the optimization present strong evidence that biplane wind turbine blades may be an enabling concept for the next generation of lighter, larger, and more cost-effective wind turbine blades.

Characteristic Analysis of DFIG Wind Turbine under Blade Mass Imbalance Fault in View of Wind Speed Spatiotemporal Distribution

The blade mass imbalance fault is one of the common faults of the DFIG (Doubly-Fed Induction Generator) wind turbines (WTs). In this paper, considering the spatiotemporal distribution of natural wind speed and the influence of wind shear and tower shadow effect, the influence of blade mass imbalance faults on the electrical characteristics of DFIG WTs is analyzed. Firstly, the analytical expressions and variation characteristics of electromagnetic torque and electromagnetic power under blade mass imbalance are derived before and after consideration of the spatiotemporal distribution of wind speed. Then simulations on the MATLAB/Simulink platform were done to verify the theoretical analysis results. The theoretical analysis and simulation results show that, considering the spatiotemporal distribution of wind speed and the influence of wind shear and tower shadow effect, the blade mass imbalance fault will cause fluctuation at the frequency of 1P (P = the frequency of rotor rotation), 3P, and 6P on electromagnetic power. Fluctuation at 1P is caused by mass imbalance while fluctuation at 3P and 6P are caused by wind speed spatiotemporal distribution; the amplitude of fluctuation at 1P is proportional to the degree of the imbalance fault. Since the equivalent wind speed has been used in this paper instead of the average wind speed, the data is more suitable for the actual operation of the WT in the natural world and can be applied for fault diagnosis in field WT operation.

Numerical Investigation of the Aeroelastic Behavior of a Wind Turbine with Iced Blades

Wind turbines installed in cold-climate regions are prone to the risks of ice accumulation which affects their aeroelastic behavior. The studies carried out on this topic so far considered icing in a few sections of the blade, mostly located in the outer part of the blade, and their influence on the loads and power production of the turbine are only analyzed. The knowledge about the influence of icing in different locations of the blade and asymmetrical icing of the blades on loads, power, and vibration behavior of the turbine is still not matured. To improve this knowledge, multiple simulation cases are needed to run with different ice accumulations on the blade considering structural and aerodynamic property changes due to ice. Such simulations can be easily run by automating the ice shape creation on aerofoil sections and two-dimensional (2-D) Computational Fluid Dynamics (CFD) analysis of those sections. The current work proposes such methodology and it is illustrated on the National Renewable Energy Laboratory (NREL) 5 MW baseline wind turbine model. The influence of symmetrical icing in different locations of the blade and asymmetrical icing of the blade assembly is analyzed on the turbine’s dynamic behavior using the aeroelastic computer-aided engineering tool FAST. The outer third of the blade produces about 50% of the turbine’s total power and severe icing in this part of the blade reduces power output and aeroelastic damping of the blade’s flapwise vibration modes. The increase in blade mass due to ice reduces its natural frequencies which can be extracted from the vibration responses of the turbine operating under turbulent wind conditions. Symmetrical icing of the blades reduces loads acting on the turbine components, whereas asymmetrical icing of the blades induces loads and vibrations in the tower, hub, and nacelle assembly at a frequency synchronous to rotational speed of the turbine.

On the wind turbine blade loads from an aeroelastic simulation and their transfer to a three-dimensional finite element model of the blade

This article first presents a description of the different load types to which a wind turbine blade is subjected. Analytical equations are derived to express blade loads from operation parameters of the wind turbine (rotor and nacelle velocities and accelerations; pitch, coning, tilt, and azimuth angles; blade mass properties; turbine geometry). This allows a better understanding of the contribution of each of these parameters to the total load on a blade. A difficulty arises for transferring the loads computed by an aeroelastic model (a one-dimensional model of the blade) to a three-dimensional finite element model of the blade. A method is proposed for that purpose. It consists in applying the aerodynamic loads using RBE3 elements and applying gravitational and inertial loads as volume forces. Finally, an example of this method used for the design of a 10 kW wind turbine blade is presented.

Numerical investigation of deep surge in a centrifugal compressor with vaned diffuser and large plenum

As the flow rate decreases from stable point to surge point, the complex unsteady flow phenomenon of surge occurs in a centrifugal compressor, which has a significant influence on vast aspects of a compressor. To advance deep understanding of the feature of the deep surge phenomenon, the RANS/URANS numerical simulation is conducted on a centrifugal compressor with a large plenum to analyze the detailed internal flow field in the compressor together with the macroscopic characteristics of the deep surge cycle. The anticlockwise limit cycle obtained from the simulation is firstly analyzed to show the transient characteristics of the stage. Then the variation of blade torque and axial force is presented to show the transient feature in surge cycle together with the proposed prediction of blade torque versus mass flow rate. Meanwhile, there exist different characteristics of the pressure fluctuation along the streamwise direction of the impeller blade, especially the large variation of blade loading near the trailing edge. And the fluctuation of flow field can respectively suppress or promote the hub-corner separation at the process of acceleration or deceleration region, affecting the development of diffuser stall in the surge cycle. The detailed analysis can be helpful to develop the surge model of lumped parameters and determine the effect of surge on impeller blades or downstream components.

Drivetrain influence on the lead–lag modes of hingeless helicopter rotors

Structural couplings between the flexible main rotor and the flexible drivetrain of the Bo105 helicopter are investigated by numerical simulation. For this purpose, the rotor hub constraint \(\varOmega ={\text {const.}}\) is dropped and a drivetrain model, consisting of discrete inertia elements and intermediate flexible elements, is connected to the hub. By use of the multibody-software SIMPACK, the coupled rotor–drivetrain system is linearized and the eigenmodes are compared to those obtained with a constrained rotor hub. The drivetrain has a significant influence on the shapes and eigenfrequencies of the collective lead–lag modes. While the first collective lead–lag eigenfrequency is raised by the finite drivetrain inertia, the second is lowered due to drivetrain flexibility. To assess the influence of modeling inaccuracies on the observed couplings, the study is complemented by a sensitivity analysis. Rotor blade mass axis offset, blade pitch (causing elastic coupling) and blade precone angle have only weak influence on the coupled modes. In contrast, variations of drivetrain inertia and stiffness strongly affect the eigenfrequencies of the coupled rotor–drivetrain modes.

Investigating the Optimal Day for Nitrogen Fertilization on Piatã palisadegrass and Quênia guineagrass after Defoliation

Considering that nitrogen is the main macronutrient limiting pasture productivity, the aim of this study was to investigate the most appropriate day for nitrogen fertilization of the grasses Brachiaria brizantha BRS Piatã and Panicum maximum BRS Quênia. The experiment was conducted in a greenhouse in the city of Rondonópolis, located in the state of Mato Grosso, Brazil, using a completely randomized design. The treatments consisted of five nitrogen fertilization periods: 0; 2; 4; 6 and 8 days after defoliation. The dry mass of the leaf blade (DMLB), dry mass of stem + sheath (DMSS), dry mass of residue (DMRES) and root dry mass (RDM) were evaluated. The non-structural carbohydrate of the grass roots was also quantified. The later nitrogen fertilization after defoliation reduced DMLB (P< .01) and DMSS (P< .01) of the BRS Piatã palisadegrass, and DMRES of both grasses (P< .01). Higher levels of water soluble carbohydrates were observed when nitrogen fertilization was performed on grass cutting (day 0). Nitrogen fertilization of the BRS Piatã palisadegrass close the time of defoliation is recommended. For Quênia guineagrass, nitrogen can be applied between the cutting day and the eighth day after defoliation. For the root system, there is a higher content of water soluble carbohydrates in the BRS Piatã palisadegrass and greater accumulation of starch in the BRS Quênia guineagrass.

The structural optimum design of laminated slender beam section with arbitrary material distribution using a genetic algorithm

In this paper, a study on optimum design methodology of a section structure of a composite material rotor blade using genetic algorithm is conducted, in order to calculate repetitive optimum design, analysis of strength, fatigue and vibration on blade section. In the analysis, the minimum mass of the rotor blade was defined as objective function; stress damage index, center of mass on blade section and fatigue life of blade were set as constraints. By applying genetic algorithm, laminate angle and thickness of skin, thickness, location and width of torsion box were established as design variables; the optimum design methodology on section structure of the composite material rotor blade was validated. The integrated design program of the section structure of the composite material rotor blade based on this study deals with designing the optimal rotor blade section which meets the design load and constraints given by the random position of rotor blade. By using blade’s section design variables derived from this, it can be facilitated for basic information on detailed design of rotor blade.

Multi-blade shedding in turbines with different casing and blade tip architectures

A shaft failure in a gas turbine engine results in the decoupling of the turbine and the compressor. The turbine continues extracting work from the air flow causing the acceleration of the free-running turbine which can result in debris release or even disc burst. Post shaft failure the structural integrity of the engine must be guaranteed for product safety and certification purposes. To achieve this, speed limiting systems have to be integrated. One common method is friction between the rotor and stationary structures which occurs during unlocated failures where the bearing arrangement allows axial movement of the rotor under end load. Another possible mechanism is the destruction of the turbine rotor blades such that they cease to extract power from the incoming flow, decelerating progressively. Blade shedding involves rupture of blades which may result in their containment within the casing or rupture of the turbine casing. This research investigates the effects of excessive damage as blades rupture in the high-pressure turbine of a large civil engine. The research investigates different casing inclinations and shrouded/unshrouded blade configurations respectively. The nonlinear finite element software LS-DYNA is used to model two blade release scenarios which are; i) simultaneous release of all blades, and ii) simultaneous sectoral release of blades. The blades are released from firtrees considering the worst case scenario from a containment point of view. It is observed that a sector having a sufficient number of blades can result in the same effect caused by all blades impacting the casing. Containment requirements of shrouded and unshrouded rotors with different casing inclinations are compared as a function of the blade kinetic energy. Provided that the blade mass is kept constant, the effect of the casing inclination is found to be dominant when compared to the effect of blade tip geometry. Together with a rotor overspeed trajectory, the containment requirement of a simultaneous multi-blade shedding application for disk burst prevention is given. The research provides improved understanding of blade tip-to-casing interactions, to be used as an overspeed prevention mechanism, and contributes towards developing design guidelines for the next generation of aero engines in terms of fail-safe engine architectures.

A Competitive-Cooperative Game Method for Multi-Objective Optimization Design of a Horizontal Axis Wind Turbine Blade

This paper presents a multi-objective optimization model of a wind turbine blade based on blade's parameterized finite element model, where annual energy production and blade mass are the objective functions, and aerodynamic and structural parameters are the design variables. In this study, the maximum axial thrust, strain, displacement, and first-order natural frequency of blade are selected as constraints. A novel competitive-cooperative game method is proposed to obtain the optimal preference solution. In this method, a new exploration method of player's strategy space named `correlation analysis under fuzzy k-means clustering' is proposed, and the payoff functions are constructed according to competitive and cooperative behaviors. Two optimization schemes with preference objectives are obtained and all goals showed clear improvements over the initial solutions, and this method reveals the relationship between blade shape and desired performance. More deeply, dynamic sensitivities of various design variables to objective functions are obtained for different blade shapes.

CARACTERÍSTICAS ESTRUTURAIS E PRODUTIVAS EM HÍBRIDOS INTRAESPECÍFICOS E INTERESPECÍFICOS DE CAPIM-ELEFANTE

Resumo Objetivou-se avaliar a estrutura e a produção de forragem em híbridos de capim-elefante manejados sob corte. Utilizaram-se como tratamentos 24 clones de capim-elefante provenientes da Embrapa Gado de Leite e o Cameroom como testemunha. Os capins foram cortados rentes ao solo, a cada 60 dias. Os parâmetros avaliados foram: produção e teor de matéria seca, número de perfilhos basais, número de folhas por perfilho, altura da planta, diâmetro do colmo. A maior altura das plantas foi observada no clone CNPGL 00-103-1. O grupo com maior número de perfilhos teve três clones e média de 39,38 perfilhos m-2. No grupo dos clones CNPGL 00-103-1, CNPGL 93-25-3, CNPGL 00-16-1 e CNPGL 00-90-3 foram observados os maiores teores de matéria seca (22,7% de MS). As maiores massas de forragem, de lâmina foliar e de colmo foram observadas no clone CNPGL 00-214, 15852 e 6195 kg ha-1 de MS respectivamente. A maior relação lâmina foliar/colmo foi do clone CNPGL 00-201-1 e apenas neste a massa de lâmina foliar foi superior à de colmo. O clone CNPGL 00-214 mostrou-se mais produtivo, com alta capacidade de perfilhamento e de acúmulo de forragem.

A framework for isogeometric‐analysis‐based optimization of wind turbine blade structures

AbstractEarly‐stage wind turbine blade design usually relies heavily on low‐fidelity structural models; high‐fidelity, finite‐element‐based structural analyses are reserved for later design stages because of their complex workflows and high computational expense. Yet, high‐fidelity structural analyses often provide design‐governing feedback such as buckling load factors. Mitigation of the issues of workflow complexity and computational expense would allow designers to utilize high‐fidelity feedback earlier, more easily, and more often in the design process. Thus, a blade analysis framework that employs isogeometric analysis (IGA), a simulation method that overcomes many of the aforementioned drawbacks associated with traditional finite element analysis (FEA), is presented. IGA directly utilizes the mathematical models generated by computer‐aided design (CAD) software, requiring less user interaction and no conversion of parametric geometries to finite element meshes. Furthermore, IGA tends to have superior per‐degree‐of‐freedom accuracy compared with traditional FEA. Issues unique to IGA in the context of wind turbine blade design, such as coupling of thin‐shell components, are addressed, and a design approach that combines reduced‐order aeroelastic analysis with IGA is outlined. Aeroelastic analysis is used to efficiently provide dynamic kinematic data for a wide range of wind load cases, while IGA is used to perform buckling analysis. The value of incorporating high‐fidelity analysis feedback into blade design is demonstrated through optimization of the NREL/SNL 5 MW wind turbine blade. A variety of potential designs are produced with reduced blade mass and material cost, and IGA‐based buckling analysis is shown to provide design‐governing constraint information.

Constructing Process Models of Engine Blade Surfaces for Their Adaptive Machining: An Optimal Approach

In a new blade manufacturing process, manufacturers precisely forge blade billets with the blade suction and the pressure surfaces within tolerance. After that, only two blade edge billets should be machined to the leading- and the trailing-edges within tolerance. If these edge design surfaces are used to generate tool paths for machining the edge billets, the machined edges are not continuous with the suction and the pressure surfaces. To address this problem, an optimal approach to constructing process models of edge surfaces is proposed for adaptive blade machining. Specifically, the modified edge surfaces are optimized within the design tolerance and are continuous with the billet suction and pressure surfaces. These surfaces are used to generate tool paths for machining the edge billets. This approach addresses the current technical challenge in the new blade manufacturing process and can substantially promote this process in blade mass production.

Optimal load frequency control in deloaded tidal power generation plant‐based interconnected hybrid power system

In recent years, power utilities have witnessed increase in penetration of tidal power generation plant (TPGP) into the power system network and, hence, it may collaborate with conventional units in frequency regulation process to ensure power system stability. Therefore, this study presents a method to monitor the participation of TPGP in load frequency control mechanisms in the presence of conventional unit such as diesel power generation plant. The participation of TPGP is showcased based on primary frequency control topologies such as by producing additional inertia, additional damping along with the concept of deloading operation. These approaches are realised by employing conventional controllers to obtain required power (corresponding to different loading conditions) from TPGP by manipulating the kinetic energy of the rotating mass of tidal turbine blades. For better performance and improved stability of the system, the controller parameters are optimised using quasi-oppositional harmony search algorithm (QOHSA). The effectiveness of QOHSA is proved by comparing the results obtained by it to those yielded by employing other existing state-of-the-art optimisation methods. The prospective analysis is validated in single-area and two-area hybrid power system models through MATLAB simulation studies.

Modeling of horizontal axis wind turbine wakes in Horns Rev offshore wind farm using an improved actuator disc model coupled with computational fluid dynamic

In order to increase the accuracy and ability to predict the total energy gained in wind farms, it is necessary to use accurate wake models. In the present study, an improved methodology is applied on actuator disc in order to take all the operational and geometrical characteristics into account such as airfoil type, angular velocity, twist, and chord distribution. In wind farms, turbines are affected by upstream ones resulting in a non-uniform upstream velocity for each turbine. However, in literature, for all the wind turbines in a wind farm, thrust coefficient curve at undisturbed wind speed is used in order to estimate the upstream speed resulting in some errors. This weakness of actuator disc is resolved by a hybrid methodology based on blade element momentum theory and mass conservation coupled with computational fluid dynamics to be independent of thrust coefficient curve and calculate more accurate incoming velocity according to operational condition. It has been observed that by using the developed model and considering the details of wind turbines and more accurate incoming wind speed, in spite of steady state simulation and low computational cost, the interaction between different turbines is well-described. For turbulence modeling, standard k-∊ turbulence model is used and it is shown that the error of power estimation in second row of turbines especially in 270° wind angle is decreased significantly. In large wind sectors, such as 270±10°, ±15°,222±10°, ±15° and 312±5°, ±10° the proposed model performs as well as LES simulation. The developed methodology is practical for designing and optimization of new wind farms even if the technical specifications such as thrust curve would not be available from manufacturer.

Analysis of leading edge flow characteristics in a mixed flow turbine under pulsating flows

Current trends in the automotive industry towards engine downsizing means turbocharging now plays a vital role in engine performance. A turbocharger increases charge air density using a turbine to extract waste energy from the exhaust gas to drive a compressor. Most turbocharger applications employ a radial inflow turbine. However, to ensure radial stacking of the blade fibers and avoid excessive blade stresses, the inlet blade angle must remain at zero degrees, creating large incidence angles. Alternately, mixed flow turbines can offer non-zero blade angles while maintaining radial stacking of the blade fibers and reducing leading edge separation at low velocity ratios. Furthermore, the physical blade cone angle introduced reduces the blade mass at the rotor outer diameter reducing rotor inertia and improving turbine transient response. The current paper investigates the performance of a mixed flow turbine under a range of pulsating inlet flow conditions. A significant variation in incidence across the LE span was observed within the pulse, where the distribution of incidence over the LE span was also found to change over the duration of the pulse. Analysis of the secondary flow structures developing within the volute shows the non-uniform flow distribution at the volute outlet is the result of the Dean effect in the housing passage. In-depth analysis of the mixed flow effect is also included, showing that poor axial flow turning ahead of the rotor was evident, particularly at the hub, resulting in modest blade angles. This work shows that the complex secondary flow structures that develop in the turbine volute are heavily influenced by the inlet pulsating flow. In turn, this significantly impacts the rotor inlet conditions and rotor losses.

Preliminary design and optimization of a 20MW reference wind turbine

We use the capabilities of a multi-disciplinary design tool to provide a definition of a 20 MW wind turbine. Starting from an aero-elastic model obtained through a classic scaling procedure, we conduct an aero-structural optimization of the rotor through a staged redesign process, in which we optimize primary characteristics of the rotor including the blade shape, the solidity and a certain amount of native structural tailoring. The process is based on a series of parametric analysis, in order to assess the impact of a variation of macro design parameters on the fundamental performance of the turbine. The redesign activity shows remarkable advantages in terms of blade mass reduction and load alleviation, highlighting directions for the development and optimization of very large rotors.