Variable Pitch Blades Research Articles

Research on the Hydrodynamic Performance of a Horizontal-Axis Tidal Current Turbine with Symmetrical Airfoil Blades Based on Swept-Back Models

For the design of a horizontal-axis tidal current turbine with adaptive variable-pitch blades, both numerical simulations and physical model experiments were used to study the hydrodynamic performance of symmetrical airfoil blades based on backward swept models. According to the lift–drag ratio of symmetrical airfoils, variable airfoil sections were selected for each part of the blade in the spanwise direction. Then, three kinds of blades were designed by using different swept-back models from wind turbines. A rotation model with a multi-reference frame was employed to conduct a three-dimensional steady numerical simulation of the turbine model based on the CFD method. The axial thrust and energy-capturing efficiency under different tip speed ratios, as well as the corresponding starting torque under different flow rates, were analyzed. The simulation results indicate that model 2 has optimal start-up performance, and model 3 has the largest power coefficient. The thrust coefficient of model 1 is the smallest. In all, model 2 has better comprehensive performance. The experiments of model 2 show that it has suitable hydrodynamic performance to capture bidirectional energy via passively variable pitch. This research provides an important solution for the design and optimization of horizontal-axis turbines to harvest bidirectional tidal current energy.

Optimal adjustment of mine fan geometry and operation

Mine fans consume significant electrical power, so it is important to ensure high efficiency of their operation. The aim of this study is to develop a method to determine the most economically efficient method to adjust axial fan geometry and operation at the maximum average efficiency in all operating modes. The method includes a developed mathematical model of the single-stage axial fan duty and a genetic algorithm for optimizing the fan parameters. The initial data for the mathematical model were the geometry of the fan blades of the average radius and the parameters of the fan operating mode. The result of the calculation was the fan efficiency in a preset operating mode. Two adjustment scenarios are modeled: fans with variable pitch blades and fans with variable rotation speed. The fan efficiency was determined by calculating the total pressure loss at the unit stage at the middle radius with regard to the loss at the blade tips. Since the mathematical model contains a large number of independent parameters, and there exists the possibility of local extrema, the optimization is performed using the genetic algorithm. The mathematical model of the fan with variable pitch blades was tested using experimental data. The error of the mathematical model in continuous modes at high efficiency (>75%) never exceeds 1.5%. As a case-study, the optimal fan parameters are determined for two preset operating modes and for two adjustment scenarios of fans with variable pitch blades and with variable rotation speed. On the basis of the obtained geometric parameters at the average radius of blades, using the constant circulation law, the fan designs were developed and then investigated by numerical simulation in CFX program. It is shown that if the air flow rate in operating modes differs significantly and the pressure is not, it is advisable to use fans with variable pitch blades.

A hybrid, self-adapting drag-lift conversion wind energy harvesting system for railway turnout monitoring on the Tibetan Plateau

Increasing numbers of turnouts are being laid, with the rapid development of high-speed railways on the Tibetan Plateau. Ensuring the proper operation of turnouts has received considerable critical attention. In this paper, a hybrid wind energy harvesting system (WEHS) based on self-adapting drag-lift conversion is designed to power high-speed railway turnout monitoring on the Tibetan Plateau. The system contains three parts: a hybrid vertical axis wind turbine (VAWT), a power generation module, and an energy storage module. Equipped with variable pitch blades, the proposed VAWT can be adaptively converted between lift mode and drag mode in upwind areas and downwind areas, respectively. A maglev generator and supercapacitor are adopted as power generation and energy storage modules. Numerical simulation indicates that the maximum power coefficient of the VAWT is 0.381. According to experiments, the maximum output power of the prototype is 2.46 W, and the maximum average power is 1.08 W. The Sichuan-Tibet Railway was adopted as a case study to investigate the feasibility and the annual power generation of the proposed system is 57.651 MWh. Results illustrate that the proposed WEHS is feasible and practical for powering high-speed railway turnout monitoring on the Tibetan Plateau.

A blade pitching approach for vertical axis wind turbines based on the free vortex method

This paper presents a variable pitch (VP) approach for a vertical axis wind turbine running at rated or higher tip speed ratios (TSRs) in order to improve the blade aerodynamic performance at the azimuth angle with a low angle of attack (AoA) and the peak power coefficient (Cp) of the wind turbine. The four largest pitch angles occurred in each quadrant in the proposed VP approach, whereas the two largest pitch angles occurred at azimuth angles of 90° and 270° n the traditional VP approaches. The free vortex model was used to predict the aerodynamic performances of the blades in the proposed VP approach and the fixed pitch (FP) blade at the designed TSR. The circulation of different vortices, the AoA, the induced velocity, and the lift coefficient obtained from the modeling results were compared for the different methods. The results indicated differences in the strength of the bound vortex and the shed vortex between the VP and FP blades at different azimuth positions. The range of the largest AoAs in the VP blade was in two big scopes, whereas the largest AoAs in the FP blade occurred only at two azimuth positions. The torque and the Cp increased at different azimuth angles, and similar trends of the AoA were observed in the azimuth angle range of 0°–360°. The differences between the VP and FP blades provided in-depth information on the performance of the proposed VP approach. The integration of the proposed VP approach and the traditional approach provides a VP strategy to control the pitch angle of the blade based on the azimuth angles and the TSRs and results in better self-starting ability at low TSRs and greater Cp at various TSRs.

A CFD investigation of a variable-pitch vertical axis hydrokinetic turbine with incorporated flow acceleration

This paper presents the numerical modelling of a novel vertical axis tidal turbine that incorporates localised flow acceleration and variable-pitch blades. The focus is to develop a computational fluid dynamics model of a 1:20 scale model of the device using ANSYS® Fluent®. A nested sliding mesh technique is presented, using an outer sliding mesh to model the turbine and additional inner sliding meshes used for each of the six blades. The turbine sliding mesh is embedded in an outer static domain which includes the flow accelerating bluff body. Modelled power performance and velocity data are compared with experimental results obtained from scale model tests in a recirculating flume. The predicted power curves show general agreement with the measured data; the relative difference in maximum performance coefficient for example, is just 5.7%. The model also accurately reproduces measured flows downstream of the turbine. The verified and experimentally validated model is subsequently used to investigate the effects of the variable-pitching and number of blades on device performance.

COMPARATIVE ANALYSIS OF FAULTS FROM STALL CONTROLLED WIND TURBINES WITH ASYNCHRONOUS GENERATORS AND PITCH CONTROLLED WIND TURBINES WITH SYNCHRONOUS GENERATORS

A large number of wind turbines from different manufacturers have been installed worldwide. They have different operating principles and are designed according to the climatic conditions of the installation site. The objective of this study is to perform a comparative analysis of the behavior of the different types of internal and external failures, their frequency and their duration for different types of wind turbines. To accomplish this, data collected directly from the Supervisory Control and Data Acquisition (SCADA) system is used to monitor two wind farms installed in Soria (Spain). The study reveals the typical faults of each type of wind turbine. Synchronous wind turbines and wind turbines with variable-pitch blades experience more types of faults; however, the frequency and duration of faults are greater in wind turbines with fixed-pitch blades and asynchronous generators. Keywords: Wind turbine, stall control, pitch control, synchronous and asynchronous generators, faults, lost time.

Effect of solidity on the performance of variable-pitch vertical axis wind turbine

The Darrieus vertical axis wind turbine (VAWT) has been the subject of a large number of recent studies to improve self-starting capability and aerodynamic performance. This study presents a computational fluid dynamics simulation of the vertical axis wind turbine with fixed and variable pitch at different solidities. In order to introduce the best efficiency value of solidity for a variable-pitch vertical axis wind turbine, a computational modeling of two-dimensional transient flow around a VAWT at solidities between 0.2 and 0.8 and turbine with two, three and four blades is conducted. The numerical simulation models the flow field around a turbine rotor by solving the strong nonlinearity of URANS and SST k-ω turbulence model, utilizing the semi-empirical numerical model. To simulate the turbine in a variable pitch method, the user-defined function (UDF) code and the moving mesh method are used. The results show that variable pitch blades with high solidities are preferred when the initial self-starting torque is required. Moreover, the variable pitch blades are capable to produce more torque at high solidities. Therefore, the vortex interaction between upwind vortices and blades in downwind stream is decreased. The results verify that the power reduction of fixed pitch VAWT at high solidities could be solved by utilizing the variable pitch technique.

An experimental study of a flow-accelerating hydrokinetic device

Tidal energy researchers and developers use experimental testing of scaled devices as a method of evaluating device performance. Much of the focus to date has been on horizontal axis turbines. This study is focused on a novel vertical axis turbine which incorporates variable-pitch blades and a flow accelerator. The research involves laboratory testing of scale model devices in a recirculating flume. Computational fluid dynamic modelling is used to reproduce the measured flow data to investigate disparities in experimental data. The results show that the device is capable of achieving localised flow acceleration of up to a factor of 2 above the freestream velocity and achieved a mechanical power efficiency of 40%.

Variable pitch blades: An approach for improving performance of Darrieus wind turbine

Unlike horizontal axis turbines, the Darrieus-type wind turbines have less efficiency and suffer from the self-starting inability. The effects of fixed and variable blade pitch angle as an idea for improving the performance of Darrieus turbine have been investigated using the CFD analysis, and a pitching system (variable pitch Darrieus-type wind turbine) has been proposed that can reduce both the blades oscillating motion and the magnitude of angle of attack in one revolution compared to that of the Darrieus-type wind turbines. In this study, the method of computational fluid dynamics with moving mesh has been used for analyzing the unsteady two-dimensional flow simulation. The numerical results show that the SST k-ω turbulence model matches well with the experimental results and can capture the flow separation phenomenon at low tip speed ratios. Also, it was observed that a small negative fixed pitch angle of −3° can delay the separation and improve the performance of wind turbine. The numerical simulation also showed that the variable-pitch blade turbine can reduce or eliminate the flow separation on its blades at a lower tip speed ratios than that of the fixed pitch blades. This result increases the starting torque and obtaining high efficiency with decreasing in torque ripple on blades during the turbine operation compared to that of the fixed-pitch blade Darrieus turbine.

可変ピッチブレードを搭載した車両型ロボットのピッチング運動制御

This paper presents a control strategy for a wheeled mobile robot with variable pitch blades which make it highly mobile over irregular terrain. In our previous work, a mathematical model with respect to pitching motion of the robot necessary to climb a stair was developed, and a nonlinear controller for the pitching motion was proposed under the assumption that the voltage to a motor for driving wheels was constant. In this paper, to improve the control performance, another controller to generate large traction acting on the wheels is proposed employing input-output linearization technique together with integral sliding mode control to provide robust performance against model uncertainties such as ground adhesion properties.

C215 可変ピッチブレードを有する車両型ロボットの制御(OS9 非線形制御理論とその応用2)

C215 可変ピッチブレードを有する車両型ロボットの制御(OS9 非線形制御理論とその応用2)

Numerical and experimental studies of a small vertical-axis wind turbine with variable-pitch straight blades

This thesis presents numerical simulations and experiments on the effect of the variable pitch angle of blade rotor on the performance of small vertical-axis wind turbines (Darrieus and Orthopter wind turbine). The power, torque, and flow around blade rotor of VAWTS were analyzed by two-dimensional unsteady computational fluid dynamics simulations using ANSYS Fluent 13.0 program. The Darrieus rotor was composed using three NACA0018 airfoil straight blades. Three different rotor blade configurations were employed which i.e., a fixed-pitch blade with a pitch angle, variable blade pitch angle. The Orthopter rotor blades rotate movement around its own axis a half relative to the main rotor in one revolution. The configurations of different aspect ratio and number of blade (of the Orthopter rotor blade were employed. The effects of the variable-pitch angle, tip speed ratio, and three turbulent models, i.e., the RNG k-e, Realizable k-e, and SST k-ω turbulent models, on the performance of Darrieus wind turbine were investigated. The effect of number of blades, tip speed ratio, and aspect ratio of the Orthopter wind turbine with flat-plate blades rotor were also investigated by numerical simulation using RNG k-e turbulent model. The result predictions of numerical were validated by open circuit wind tunnel experimental data. The numerical simulations results of both a VAWT with variable pitch blade and the orthopter wind turbine had good qualitative agreement with the experiments results. The predictions of performance of using the RNG k-e turbulence model were very close with experimental data. The VAWT with variable-pitch blades has better performance than a VAWT with fixed-pitch blades and by RNG k-e and SST k-ω turbulent models, its can suppress the occurrence of a vortex on its blades at a low tip speed ratio. The performance of the Orthopter is influenced by aspect ratio, number of blade, and tip speed ratio. The highest performance of Orthopter wind turbine at AR=1. The high tip speed ratio lead to reducing torque generation especially at downstream area. The simulations show effects of number of blade on the performance. The high number of blade reduces torque generation of one blade. However, the overall of performance was increased.

Experimental research on tidal current vertical axis turbine with variable-pitch blades

Due to the limited storage and ever-increasing dependence on fossil fuel, the world is in the phase of shifting toward renewable energy. Tidal current energy is one of the most predictable forms of renewable energy, which is harnessed by utilizing a tidal current turbine. To study the performance of the tidal current turbine relating to the ability of energy absorption and exchanging, experimental tests play an important role which can not only validate the numerical results but also provide a reference for the prototype design. In this study, a series of experiments related to vertical-axis turbines (VAT) were carried out at Harbin Engineering University and a large quantity of experimental data to study the hydrodynamic performance of turbines was presented. Based on the different techniques used to control the pitch mechanism, the experiments can be classified as the cycloid type controllable-pitch, spring-control pitch and passive variable-pitch VAT experiment. The influences of the different parameters on the hydrodynamic performance of turbines were discussed. Finally, some control strategies for the blade for different turbines were given.

715 可変ピッチブレードを有する車両型ロボットの開発(GS07-1 ロボティクス・メカトロニクス)

715 可変ピッチブレードを有する車両型ロボットの開発(GS07-1 ロボティクス・メカトロニクス)

Performance of Pitch and Stall Regulated Tidal Stream Turbines

Controllers for a pitch and a stall regulated horizontal axial flow, variable-speed tidal stream turbine are developed, and a performance comparison is carried out. Below rated flow speed, both turbines are operated in variable-speed mode so that the optimum tip-speed ratio is maintained. One of the turbines has variable pitch blades, which above rated speed are pitched to feather in order to regulate power. The other turbine has fixed pitch blades and uses speed-assisted stall to regulate power. The control system design behind both strategies is examined in MATLAB, with the performance under turbulent flows, loading and energy yield analysis being evaluated in GH Tidal Bladed. Both strategies provide a satisfactory performance, but the out-of-plane loads on the stall regulated turbine were higher over the entire range of operation. In addition, the dynamic characteristics of the stall regulated turbine require a more complex control design. The results suggest that the pitch regulated turbine would be a more attractive solution for turbine developers.

Performance of a hydrokinetic energy system using an axial-flux permanent magnet generator

The high density of water has been an important factor for harnessing kinetic energy from marine current flows, tides, flowing rivers, or other artificial water channels. Thus, new technologies are being developed to generate electricity. A good example is HKES (hydrokinetic energy systems), which are devices that extract and convert energy from the motion of flowing water into electricity. Although these non-polluting machines and/or devices are still in their pilot phases, they have been growing as a sustainable source of new electric power generation. In this paper, the performance of a horizontal hydrokinetic energy system with variable-pitch blades using an axial-flux generator is evaluated. Particularly, very simple sheet blades have been used to keep system cost down. The evaluation is based on maximum power extraction and energy conversion efficiency normalized by system cost through a simpler electro-mechanical design for the hydrokinetic system. Experimental results have demonstrated that the proposed prototype possesses higher efficiency with reduced energy losses and manufacturing costs. It represents a cost-competitive alternative energy for power supply for civilian applications in remote areas or an option for expeditionary applications.

0211 可変ピッチ式抗力型垂直軸風車の性能に及ぼす翼形状の影響(OS12 自然と生物の流れ現象とその有効利用,オーガナイズドセッション 12:「自然と生物の流れ現象とその有効利用」)

0211 可変ピッチ式抗力型垂直軸風車の性能に及ぼす翼形状の影響(OS12 自然と生物の流れ現象とその有効利用,オーガナイズドセッション 12:「自然と生物の流れ現象とその有効利用」)

Turbulence and Secondary Flows in an Axial Flow Fan With Variable Pitch Blades

This paper analyzes the structure of turbulence and secondary flows at the exit of an axial flow fan with variable pitch blades. The influence of changing the blades’ pitch angle over the turbulent structures is assessed by means of turbulence intensity values and integral length scales, obtained by using hot-wire anemometry for several test conditions. Since total unsteadiness is composed of both periodic and random unsteadiness, it is necessary to filter deterministic unsteadiness from the raw velocity traces in order to obtain turbulence data. Consequently, coherent flow structures were decoupled and thus, levels of turbulence—rms values of random fluctuations—were determined using a filtering procedure that removes all the contributions stemming from the rotational frequency, the blade passing frequency, and its harmonics. The results, shown in terms of phase-averaged distributions in the relative frame of reference, revealed valuable information about the transport of the turbulent structures in the unsteady, deterministic flow patterns. The anisotropic turbulence generated at the shear layers of the blade wakes was identified as a major mechanism of turbulence generation, and significant links between the blade pitch angle and the wake turbulent intensity were established. In addition, the autocorrelation analysis of random fluctuations was also used to estimate integral length scales—larger eddy sizes—of turbulence, providing useful data for computational fluid dynamics applications based on large eddy simulation algorithms. Finally, contours of radial vorticity and helicity gave a detailed picture of the vortical characteristics of the flow patterns, and the definition of secondary flow as the deviation of the streamwise component from the inviscid kinematics was introduced to determine the efficiency of the blade design in the energy exchange of the rotor.

102 尾翼を有した揺動翼式垂直軸風車の性能特性(OS7-1 自然と生物の流れ現象とその有効利用(1),オーガナイズドセッション:7 自然と生物の流れ現象とその有効利用)

102 尾翼を有した揺動翼式垂直軸風車の性能特性(OS7-1 自然と生物の流れ現象とその有効利用(1),オーガナイズドセッション:7 自然と生物の流れ現象とその有効利用)

101 リンク機構による可変ピッチ角直線翼垂直軸風車の性能特性 : 翼形の影響(OS7-1 自然と生物の流れ現象とその有効利用(1),オーガナイズドセッション:7 自然と生物の流れ現象とその有効利用)

101 リンク機構による可変ピッチ角直線翼垂直軸風車の性能特性 : 翼形の影響(OS7-1 自然と生物の流れ現象とその有効利用(1),オーガナイズドセッション:7 自然と生物の流れ現象とその有効利用)