Twist Angle Distribution Research Articles

Small Wind Turbine Design Verification by Computer Simulation

Rotor blade design relies heavily on the aerodynamic theory. Extensive calculations are necessary in order to determine the blade parameters such as chord and thickness distributions, twist angle distribution and taper that is matched with the selected airfoil sections. For practical purposes, the engineers need a convenient means to verify their design. Wind turbine blades must be designed to operate in desirable performance. This research proposes a computer aided method that helps the engineers to examine the design and amend it in time. The numerical example shows good applicability of the methodology proposed. The proposed methodology not only lets us verify our design scientifically but also makes us understand the associated physical insight. The numerical example demonstrated here showed the converted power by the rotor can be evaluated easily by Flow Simulation according to the aerodynamics theory.

開断面と閉断面を組み合わせた二重筒によるTwist型モーフィング翼桁構造

A new concept of twistable morphing spar is proposed to achieve an objective distribution of the twist angle more arbitrary and validity of the proposed design method is confirmed through experiments and numerical simulations using finite element analyses. A key aspect of the proposed twistable morphing spar concept is a double cylinder consisting of two cylinders, which is employed as a spar of twistable morphing wing. The ends of these cylinders are connected to each other at the tip side. One cylinder (Inner-cylinder) is a thick closed-section member. It carries torsion moments and connected to motor that provides moment to the member at the root side. The other cylinder (Outer-cylinder) is a variable-shape member composed of open and closed-sections. It is designed to achieve an objective distribution of twist angles, and is connected to the aircraft fuselage at the root side. The objective distribution of the twist angle can be achieved by designing the parameter we selected appropriate. In accordance with the design method, we manufactured an experimental model using a 3D printer and twist experiment was carried out. From comparison of the experimental results and the numerical simulation, feasibility of the twistable morphing spar and the validity of the design method were confirmed.

Proposal for a coupled aerodynamic–structural wind turbine blade optimization

An advanced design algorithm for the AOC 15/50 wind turbine is hereby presented: both aerodynamic and structural parameters are considered as the design variables for a coupled BEM–FEM optimization.In order to obtain an improvement in rotor blade design, a modified version of the S.O.C.R.A.TE. algorithm combines a BEM evaluation of its aerodynamic performance, a FEM structural analysis and a genetic algorithm. Both the aerodynamic power (resulting from the BEM analysis) and the tip displacement (produced by the aerodynamic forces and the inertial loads) are considered as the fitness functions for the optimization problem.An improved distribution of both chord values and twist angles is determined, as well as an optimal layout of the blade composite skin. A slight increase in the aerodynamic power generation is obtained, as well as a marked improvement in overall blade deformation characteristics.

Aerodynamic shape optimization and analysis of small wind turbine blades employing the Viterna approach for post-stall region

This paper aims to optimize the distribution of chord and twist angle of small wind turbine blade in order to maximize its Annual Energy Production (AEP). A horizontal-axis wind turbine (HAWT) blade is optimized using a calculation code based on the Blade Element Momentum (BEM) theory. A difficult task in the implementation of the BEM theory is the correct representation of the lift and drag coefficients at post-stall regime. In this research, the method based on the Viterna equations was used for extrapolating airfoil data into the post-stall regime and the results were compared with various mathematical models. Results showed the high capability of this method to predict the performance of wind turbines. Evaluation of the efficiency of wind turbine blade designed with the proposed model shows that the optimum design parameters gave rise to an increase of 8.51% in the AEP rate as compared with the corresponding manufactured operating parameters.

Aerodynamic optimization of the blades of diffuser-augmented wind turbines

Adding an exit diffuser is known to allow wind turbines to exceed the classical Betz–Joukowsky limit for a bare turbine. It is not clear, however, if there is a limit for diffuser-augmented turbines or whether the structural and other costs of the diffuser outweigh any gain in power. This work presents a new approach to the aerodynamic optimization of a wind turbine with a diffuser. It is based on an extension of the well-known Blade Element Theory and a simple model for diffuser efficiency. It is assumed that the same conditions for the axial velocity in the wake of an ordinary wind turbine can be applied on the flow far downwind of the diffuser outlet. An algorithm to optimize the blade chord and twist angle distributions in the presence of a diffuser was developed and implemented. As a result, an aerodynamic improvement of the turbine rotor geometry was achieved with the blade shape sensitive to the diffuser speed-up ratio. In order to evaluate the proposed approach, a comparison with the classical Glauert optimization was performed for a flanged diffuser, which increased the efficiency. In addition, a comparative assessment was made with experimental results available in the literature, suggesting better performance for the rotor designed with the proposed optimization procedure.

Design, analysis and test of a model turbine blade for a wave basin test of floating wind turbines

Froude scaling is a generally reliable way to design models of floating wind turbines for wave basin testing. However, the resulting rotor thrust of the model is far lower than the Froude-scaled value of a full-size turbine, because the reduction in Reynolds number decreases the lift coefficients and increases the drag coefficients (the Reynolds number scaling effect). A 1/50th scale model wind turbine based on a NREL-5MW reference turbine is examined here. To mitigate the Reynolds number scaling effect in the model, the original aerofoils of the reference turbine (DU series and NACA 64-618) were replaced by an aerofoil at a low Reynolds number (NACA 4412). Such a model with aerofoil-adjusted blades was used in the mathematical optimization of rotor thrust. The design objective was to guarantee that while the rotor thrust of the model equalled the Froude-scaled rotor thrust of the reference, the smallest chord lengths were achieved, considering the weight control in building the model blade. The distribution of chord lengths fitted a fourth-order polynomial curve, and the distribution of twist angles along the blade fitted a second-order polynomial curve. The eight coefficients of the two curves were chosen as optimization variables, and pattern search method was used to solve the optimization model. The model blade was designed at zero pitch angle and further tested in FAST, a fully coupled simulation tool. A model test was conducted using the optimized blade geometry in the State Key Laboratory of Ocean Engineering in Shanghai, China, and the thrusts were compared with the predicted values.

Propeller Design and Loss Mechanisms in Low-Reynolds-Number Flows

To develop a highly efficient propeller for small-scale unmanned aerial vehicles, the influences of induced and profile losses determined by design parameters are investigated at . The propeller blade shapes, such as chord length and twist angle distributions in the spanwise direction, are determined using the Adkins–Liebeck method. For a fixed designated thrust value and a forward velocity, the influences of a propeller normalized radius, a blade number, and a tip speed ratio on the propeller performance are discussed. Results show that the profile loss can be larger than the induced loss. For such a case, it is beneficial to reduce the blade number and the propeller rotational speed to increase the blade chord length and the Reynolds number; consequently, the propeller efficiency increases even if the induced drag increases.

NanoARPES of twisted bilayer graphene on SiC: absence of velocity renormalization for small angles.

The structural and electronic properties of twisted bilayer graphene (TBG) on SiC(000) grown by Si flux-assisted molecular beam epitaxy were investigated using scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy with nanometric spatial resolution. STM images revealed a wide distribution of twist angles between the two graphene layers. The electronic structure recorded in single TBG grains showed two closely-spaced Dirac π bands associated to the two stacked layers with respective twist angles in the range 1–3°. The renormalization of velocity predicted in previous theoretical calculations for small twist angles was not observed.

Transparent Boundary Condition for Oseen-Frank Model. Application for NLC Cells With Patterned Electrodes

In the present work a novel application of Transparent Boundary Conditions (TBC) to nematic liquid crystal cells (NLCC) with planar alignment and a patterned electrode is studied. This device is attracting great interest since it allows soliton steering by optically and externally induced waveguides. We employ the continuum Oseen-Frank theory to find the tilt and twist angle distributions in the cell under the one-constant approximation. The electric field distribution takes into account the whole 2D permittivity tensor for the transverse coordinates. Standard finite difference time domain methods together with an iterative method is applied to find an approximate solution to our coupled problem. A novel class of TBC is used to correctly define the boundary for both the distortion angle problem and the electric field distribution when using patterned electrodes. Thus, we achieve an important decrease of computational needs when solving this kind of problems and we are also capable of exploring weak anchoring conditions for NLCC.

Design & optimization of a small wind turbine blade for operation at low wind speed

A small wind turbine blade was designed and optimized in this research paper. The blade plays an important role, because it is the most important part of the energy absorption system. Consequently, the blade has to be designed carefully to enable to absorb energy with its greatest efficiency. The main objective of this paper is to optimized blade number and selection of tip speed ratio corresponding to the solidity. The power performance of small horizontal axis wind turbines was simulated in detail using blade element momentum methods (BEM). In this paper for wind blade design various factors such as tip loss, hub loss, drag coefficient, and wake were considered. The design process includes the selection of the wind turbine type and the determination of the blade airfoil, twist angle distribution along the radius, and chord length distribution along the radius. A parametric study that will determine if the optimized values of blade twist angle and chord length create the most efficient blade geometry. The 3-bladed, 5-bladed and 7-bladed rotor achieved maximum values of Cp 0.46, 0.5 and 0.48 at the tip speed ratio 7, 5 and 4 respectively. It was observed that using BEM theory, maximum Cp varied with strongly solidity and weakly with the blade number. The studies showed that the power coefficient increases upto blade number B = 5, while the blade number if increased above 5 then the power coefficient decreases at operating pitch angle equal to 3°. Highest Cp would have solidity between 4% to 6% for number of blade 3 and design point tip speed ratio of about "7". Highest Cp would have solidity ranging from 5% to 10% for number of blade 5 and 7 and design point tip speed ratio of about 5 and 4 respectively.

A Direct Approach of Design Optimization for Small Horizontal Axis Wind Turbine Blades

The performance of a wind turbine rotor depends on the wind characteristics of the site and the aerodynamic shape of the blades. The blade geometry determines the torque and the power generated by the rotor. From aerodynamic point of view, an economic and efficient blade design is attained by the maximization of rotor power coefficient. For small wind turbine blade design, there are some factors different from large blade. Such as, the small ones experience much lower Reynolds number flow than the large ones, thus large wind turbine airfoils may perform very poorly in small applications. The small turbines are self-started at lower wind speed, thus the hub and tip parts are vital for the starting-up torque which should be able to conquer the resistance of the generator and the mechanical system. This paper presents a direct method for small wind turbine blade design and optimization. A unique aerodynamic mathematical model was developed to obtain the optimal blade chord and twist angle distributions along the blade span. The airfoil profile analysis was integrated in this approach. The Reynolds number effects, tip and hub effects, and drag effects were all considered in the design optimization. The optimal chords and twist angles were provided with series of splines and points and three-dimensional blade models. This approach integrates blade design and airfoil analysis process, and enables seamless link with computational fluid dynamics analysis and CNC manufacturing.

An Iterative Method to Optimize the Twist Angle of a Wind Turbine Rotor Blade

Maximizing the power output of a wind turbine is possible by ensuring the airfoils along the blade operate at an optimal angle of attack. However, blades deflect under loading but the torsional deflection of wind turbine blades is normally ignored in the blade design process. Since the power output is dependent upon the blade twist angle, an optimized blade shape must take into account the torsional deflection of the blade. The torsional deflection changes the loading of the blade. This necessitates iterative methods to determine the equilibrium loading and deflection and to optimize the blade shape. This paper explains a method to determine the equilibrium torsional deflection of the blade and a method to determine the optimal static blade twist angle to maximize power production. The results are the blade twist angle distribution that will deform to an optimal angle of attack under load, thereby changing the peak of the coefficient of power ( CP) curve to a chosen wind speed.

Raman mapping investigation of chemical vapor deposition-fabricated twisted bilayer graphene with irregular grains.

Bilayer graphene as a prototype of two-dimensional stacked material has recently attracted great attention. The twist angle between graphene layers adds another dimension to control its properties. In this study, we used Raman mapping to investigate the twist angle dependence of properties of twisted bilayer graphene (TBG) with irregular grains that was fabricated by chemical vapor deposition (CVD). Different Raman parameters including intensity, width, and position of G and 2D peaks were used to distinguish TBG with different twist angles. The statistical results from Raman imaging on the distribution of twist angle are consistent with the results from selected area election diffraction (SAED). Finally, the Raman peak at approximately 1347 cm(-1) for TBG with a large twist angle was assigned to the D-like peak, although it has similar excitation energy dependence of frequency as the defect-induced D peak. Theoretical calculation further confirmed that vacancy-like defect is not favored in the formation energy for TBG with a large twist angle as compared to monolayer graphene or TBG with other twist angles. These results will help to advance the understanding of TBG properties, especially for CVD samples with irregular grains.

Effect of Selection of Design Parameters on the Optimization of a Horizontal Axis Wind Turbine via Genetic Algorithm

The effect of selecting the twist angle and chord length distributions on the wind turbine blade design was investigated by performing aerodynamic optimization of a two-bladed stall regulated horizontal axis wind turbine. Twist angle and chord length distributions were defined using Bezier curve using 3, 5, 7 and 9 control points uniformly distributed along the span. Optimizations performed using a micro-genetic algorithm with populations composed of 5, 10, 15, 20 individuals showed that, the number of control points clearly affected the outcome of the process; however the effects were different for different population sizes. The results also showed the superiority of micro-genetic algorithm over a standard genetic algorithm, for the selected population sizes. Optimizations were also performed using a macroevolutionary algorithm and the resulting best blade design was compared with that yielded by micro-genetic algorithm.

A Complete Procedure for Predicting and Improving the Performance of HAWT's

A complete procedure for predicting and improving the performance of the horizontal axis wind turbine (HAWT) has been developed. The first process is predicting the power extracted by the turbine and the derived rotor torque, which should be identical to that of the drive unit. The BEM method and a developed post-stall treatment for resolving stall-regulated HAWT is incorporated in the prediction. For that, a modified stall-regulated prediction model, which can predict the HAWT performance over the operating range of oncoming wind velocity, is derived from existing models. The model involves radius and chord, which has made it more general in applications for predicting the performance of different scales and rotor shapes of HAWTs. The second process is modifying the rotor shape by an optimization process, which can be applied to any existing HAWT, to improve its performance. A gradient- based optimization is used for adjusting the chord and twist angle distribution of the rotor blade to increase the extraction of the power while keeping the drive torque constant, thus the same drive unit can be kept. The final process is testing the modified turbine to predict its enhanced performance. The procedure is applied to NREL phase-VI 10kW as a baseline turbine. The study has proven the applicability of the developed model in predicting the performance of the baseline as well as the optimized turbine. In addition, the optimization method has shown that the power coefficient can be increased while keeping same design rotational speed.

Aerodynamic Design of a Horizontal Axis Micro Wind Turbine Blade Using NACA 4412 Profile

Wind turbine blade is a key element to convert wind energy in to mechanical power. This work presents functional design and aerodynamic design of an eight hundred mm long blade of a six hundred W horizontal axis micro wind turbine using NACA4412 profile. Functional design of blade is carried out by considering use of electrical appliances to meet need of a rural house for low wind speed region. Various theories are available and used by designers for blade design. The chord and twist angle distributions of the preliminary blade design are determined. The preliminary blade design does not necessarily provide the best power performance under practical operation conditions and needs to follow further modifications and calculations. Also, a reasonable compromise between high efficiency and good staring is expected. The optimization with the objective of enhancement of power performance and low speed starting behavior is carried out. Though, hub region contributes little to overall power production, its optimization plays important role for good starting and low wind performance. In this work analysis is carried out for coefficient of performance of the blade and for starting behavior of the wind turbine blade. MATLAB programming is developed for the blades. The power coefficients curves are drawn for the optimized wind turbine.

Formation and structural analysis of twisted bilayer graphene on Ni(111) thin films

We synthesized twisted bilayer graphene on single crystalline Ni(111) thin films to analyze the statistical twist angle distribution on a large scale. The twisted bilayer graphene was formed by combining two growth methods, namely the catalytic surface reaction of hydrocarbons and carbon segregation from Ni. Low energy electron diffraction (LEED) investigations directly revealed dominant twist angles of 13°, 22°, 38°, and 47°. We show that the angle distribution is closely related to the sizes of Moiré superlattices which form at commensurate rotation angles. In addition to the commensurate angles, quasi-periodic Moiré structures were also formed in the vicinity of the dominant angles, confirmed by microscopic observations with low energy electron microscopy and scanning tunneling microscopy (STM). The quasi-periodic Moiré patterns are presumably caused by insufficient mobility of carbon atoms during the segregation growth while cooling. Micro-LEED studies reveal that the size of single twisted domains is below 400nm. Atomic-scale characterization by STM indicates that the twisted layer grown by segregation is located underneath the layer grown by surface reaction, i.e. between the Ni surface and the top single-crystal graphene layer.

Aerodynamic design and economical evaluation of site specific horizontal axis wind turbine (HAWT)

This paper presents the aerodynamic design and economical evaluation of a 200 kW site specific wind turbine for the province of Semnan in Iran. By designing site specific wind turbines, the cost of energy which is calculated out of the annual energy production and also the cost of manufacturing the rotor are minimized. The aerodynamic design is based on the well-known blade element momentum theory (BEM) which is integrated with annual wind distribution of the designated wind site to determine the net annual electricity yield for two designed rotors. In the first rotor, a linear fit approximation is used for the chord length and twist angle distributions for ease of manufacturing and to overcome technological barriers in Iran. In the second rotor, the optimum original nonlinear distribution of the blade is assumed. The RISO-A-24 aerofoil is used and optimized for the design tip speed ratio of λ=8.93 for both rotors. Pitch angle control is also adopted here. A comparison is made between the aerodynamic performance and decrease of manufacturing costs for both rotors. The economic feasibility indicates that based on current electricity costs of 12 cent per kWh in Iran for renewable energies, a profit of 7.2 cent and 8.1 cent per each kWh generated power is achievable respectively by the linear and nonlinear rotor designs. Therefore, the scenario of reducing initial costs is not recommended unless technological shortcoming in manufacturing rotor cannot be avoided.

Conformational Properties of Kinesin's Neck Linker Across Species

Kinesin I, a homodimeric motor protein facilitates the movement of cellular cargo and vesicles toward the membrane, using microtubules as a bridge. Kinesin contains a short disordered neck linker region between the motor head and ordered stalk. The flexibility of the neck linker is a key parameter that governs the overall properties of the kinesin stepping mechanism. However, to date, our knowledge about the molecular structure and dynamics of this region remains incomplete. In order to explore its mechanical properties and propensity for preferred conformations, we conducted 1 microsecond implicit solvent molecular dynamic simulations using Gromacs with the AMBER force field. We analyzed the overall twist angle of the neck linker as a function of time and found that the twist angle distribution is bimodal indicating that the neck linker may have two preferred conformations. To determine the generality of this result, we ran simulations on disordered neck linker regions from multiple species including fruit fly, human and mouse and found that this appeared to be a generic feature of the kinesin I neck linker region.

Optimal Design of Wind Turbine Blades with Wilson and BEM Method Integrated

This paper presented a new dynamic optimal design method of wind turbine blade which combined the Wilson model with the BEM aerodynamic model. Considering the wind energy utilization coefficient as the target function, the Wilson theory was used to optimize a 1.5MW blades aerodynamic shape. The revised distribution of chord and twist angle was nearly of linear change in the main output power section of blade. The optimized wind energy utilization coefficient can reach 0.552, which is very closed to the Betz limitation. In the part of the calculation of aerodynamic performance, considering both the effect of solidity and eddy current loss on the aerodynamic performance calculation, and also considering the sensitivity of the initial value in a nonlinear equation, it utilized the blade element momentum theory (BEM) which was a classical method on the aerodynamic performance of blade to calculate the aerodynamic performance.The results shows the optimized power output can be up to 1.3426MW, and compared with the rated power, the efficiency reached 89%.