Tidal Current Turbine Research Articles

Linear and non-linear wave theories coupled with a modified BEM model for quantifying dynamic loads of a tidal stream turbine

Dynamic loads resulted from wave-current interaction is a serious problem facing tidal current turbines (TCTs), which may lead to catastrophic results. The main issue in such environments is the accelerated fatigue, which likely results from the cyclic loading especially in the axial direction. For investigating the current effects on the wave field and evaluating the resulted dynamic loads, a modified Blade Element Momentum (BEM) model was presented and coupled with linear and non-linear wave theories.Firstly, a validation study has been performed between the present modified BEM model coupled with linear wave theory and previous numerical and experimental results. A previously introduced dynamic inflow model was reemployed in the present BEM model during this validation to assess its applicability and accuracy. Very good agreements were seen between the present model and the experimental data at different wave properties and operational conditions, which emphasized the precision of the present unsteady BEM model and its corrections for further investigations.Comparing with other operational conditions, the intrinsic wave period and wave height had significant effects on the resulted hydrodynamic loading ranges of both the blade root bending moments. By the use of linear wave theory, the resulted out-of-plane bending moment was under predicted. Linear wave and second-order models had similar bending moments at all wave and flow conditions. Due to considering the current effects on wave properties, Dean's, third-order and fifth-order models had dynamic loadings differed in phase, frequency and amplitude from the experimental data. Fifth-order model was finally considered the best choice for simulating the wave-current velocity at different wave conditions and immersion depths.An additional complete time series runs were performed to assess the effect of dynamic stall correction inclusion in the present BEM model on the resulted hydrodynamic loads. It had minor effects on the bending moments, while had noticeable influence on the turbine thrust.

Influence of blade numbers on start-up performance of vertical axis tidal current turbines

To alleviate the energy crisis, the tidal energy extraction has become a hot topic in recent years. As a commonly utilized energy converter, a primary concern of vertical axis tidal turbines (VATTs) is the incapability to self-start. Previous studies have found that the starting performance has a great correlation with the number of blades. However, the detailed effects of blade number on starting characteristic are not fully understood. Therefore, it is necessary to further assess the influences of the number and azimuthal angle of blades on starting characteristics. In this study, we investigate the effects of the blade number on start-up performance of VATTs by means of the commercial Computational Fluid Dynamic (CFD) software CFX. It can be seen that the increase of the blade number results in a more homogeneous flow field, and the varying angles can lead to a high average torque. Besides, the region of 100°–120° is proved that all turbines with three different blade numbers can achieve a better starting performance.

Performance and wake analysis of horizontal axis tidal current turbine using Improved Delayed Detached Eddy Simulation

This paper presents the results of hydrodynamic performance and wake assessment for a horizontal axis tidal current turbine. The three-dimensional instantaneous flow field is resolved utilizing the Improved Delayed Detached Eddy Simulation (IDDES) turbulence model and polyhedral mesh. The rotor rotation is simulated by employing the sliding mesh approach. The simulation results using turbulence model of k-ω Shear Stress Transport are also presented for comparison. The simulated thrust and power coefficients and wake characteristics are validated against published experimental results. It is shown that the performance and wake velocity predicted by IDDES are closer to the experimental values than those predicted by k-ω Shear Stress Transport model. In determining the pressure coefficient, only IDDES captures the time-varying fluctuations pertaining to blade generated turbulence. The oscillations in phase-averaged performance coefficients are substantially larger for IDDES because the inflow turbulence in this model is more realistically resolved using Synthetic Eddy Method. The IDDES predicts more detailed vortex structures which has impact on accurate determination of blade pressure distribution, energy dissipation rate and downstream flow field. It is demonstrated that the IDDES model is capable to satisfactorily simulate the hydrodynamics of a horizontal axis tidal current turbine.

The Blade Design of a Bionic Shark Fin Airfoil for a Horizontal Axis Tidal Current Turbine

AbstractThe horizontal axis tidal turbine is a typical apparatus to capture the energy in the ocean, but most traditional design methods of a turbine blade have led to the inefficiency of turbines....

Influence of helical triangle blade on the performance of vertical axis marine current turbine

The vertical axis marine current turbine is emerging as a promising candidate for renewable energy applications, while its wide application is currently limited by low and unsteady power output. In this paper, the influence of helical triangle blade on the performance of vertical axis marine current turbine has been investigated. Four types of helical triangle blades with helical wrap angle of 15°, 30°, 45° and 60° at half blade height have been studied, and compared with conventional straight blades. It is found that the stability of the power output of the turbines is improved by the helical triangle blade with the increase of helical wrap angle up to 15°. The helical triangle blade with 15° helical wrap angle named as “HT blade” has the best performance. Its maximum improvement of power coefficient is 13.4% as well as improvement of the stability of power output. Furthermore, we confirmed that HT blade effectively reduced the scale of wake and stall vortex as well as the amplitude of pressure fluctuation on its surface compared to that of the original straight blade. Therefore, the properly-designed helical triangle blades are conducive to the operation stability and power output of the vertical axis tidal current turbines.

Study on characteristics of turbine wake and the effect of array arrangement

A prerequisite in undertaking large-scale developments and utilisation of tidal current energy is to comprehend the hydrodynamic characteristics of the wake field of tidal current turbines. The wake of an upstream turbine can strongly affect the power output of downstream turbines and their arrangement. The structure of turbine wakes was investigated. One experiment was conducted on a two-bladed horizontal turbine in a laboratory flume. Actuator disc momentum theory, combined with Reynolds-averaged Navier–Stokes equations, was used to parameterise the tidal turbine. The numerical model was validated using experimental data. The degree of wake mixing improved when the axial distance was eight times the turbine diameter (8D) or larger. The influence of the arrangement and spacing of turbines was investigated at two tidal farms, one with three aligned turbines and one with seven staggered turbines. The incoming flow velocity of the downstream turbine was reduced by 31% when turbines were linearly aligned. The extent of influence of the third column was larger than that of the second column, indicating an expanding wake. Different lateral spaces of staggered turbines were analysed. Different distances between rows strongly influenced both the incoming velocity of downstream turbines and the expansion of the whole wake. The incoming flow of the third column reduced by 31, 17 and 16% with increasing lateral space. The flow velocity increased as water passed over the turbine tip. For staggered turbines, a centreline spacing of up to 1.5D for adjacent rows is recommended.

A combined method of CFD simulation and modified Beddoes-Leishman model to predict the dynamic stall characterizations of S809 airfoil

The Beddoes-Leishman model (B-L model) was widely applied in the airfoil's dynamic loads prediction. But the need for numerous experimental parameters greatly limits its application range. In this study, numerical simulation was used to simulate the wind tunnel experiments of airfoils to obtain the required parameters. Take the S809 and NACA0012 airfoils as examples, Fluent software was used to calculate the static parameters, and dynamic mesh technology was used to simulate the sinusoidal oscillation wind tunnel experiments of airfoils to obtain the dynamic parameters. Use the modified B-L model with the obtained parameters to predict the dynamic stall characteristics of the airfoils. The predicted results are in good agreement with the experimental data of the wind tunnel, which means that it is promising to use numerical simulation to calculate the parameters required by the B-L model to predict the dynamic stall characteristics of an airfoil. It provides a simpler and more feasible method for predicting the dynamic loads of the blade of wind turbines and tidal current turbines.

Blade Profile Design and Optimization of Ocean Energy Low-speed Water Turbine

Based on multi-objective genetic algorithm, naca4415 airfoil (NACA airfoil is a series of airfoils developed by the National Aeronautical Advisory Committee of the United States) is used as the original airfoil to optimize the blade airfoil of low water speed tidal current turbine, The lift drag ratio of the generator airfoil is improved (lift drag parameter is one of the key factors to determine the low-speed water kinetic energy conversion efficiency of the airfoil), the power generation efficiency of the turbine airfoil is improved, and the s airfoil is spliced on the basis of the optimized airfoil. The results show that the lift drag ratio performance of the optimized airfoil at the designed angle of attack is improved compared with that of the unoptimized airfoil, and the lifting range increases with the increase of the angle of attack. The pressure coefficient of the optimized airfoil decreases and the flow velocity increases. The pressure coefficient of the assembled S-shaped airfoil and the S-shaped airfoil have good bi-directional energy harvesting performance at the optimal attack angle of 12° to 15 °

Experimental investigation into the improvement of self-starting capability of vertical-axis tidal current turbine

Indonesia has a lot of tidal current energy resources that can be harnessed using a vertical-axis turbine. However, one of the disadvantages of the vertical-axis turbine is its low self-starting capability. Under the actual condition, tidal current velocity is fluctuated and sometimes is very low, making the turbine unable to rotate. The purpose of this study is to investigate and improve the self-starting capability of a vertical-axis turbine. The study was conducted experimentally using a towing tank in Institut Teknologi Sepuluh Nopember (ITS) at Surabaya, Indonesia. The speed of towing carriage was set with the starting condition of 0 up to 0.4 m/s with an increment of 0.1 m/s. The stages of the test are as follows: first, the original vertical-axis turbine, a turbine with three straight-blades, was investigated; second, the modified vertical-axis turbine (inclined-blade) was proposed to increase the self-starting capability. The inclined-blade turbine has smooth self-start characteristics compared with the straight-blade turbine. It can start rotating at 0.2 m/s with a turbine rotation speed of 2.25 rpm. The original vertical-axis turbine with straight blades can start rotating at 0.3 m/s with a turbine rotation speed of 1.93 rpm. Therefore, a vertical-axis turbine modified with inclined-blades has better self-start capability that is suitable to implement in an area with low tidal current velocity.

An effective framework for wake predictions of tidal-current turbines

Deployment of tidal array farms is the next stage of tidal energy development which concentrates on the capture of the enormous energy. Characterization into the wake of tidal turbine aids in determining the tidal farm layout and energy yields. This paper develops a framework that employs the Computational Fluid Dynamics (CFD) simulation and machine learning to analyze turbine wake with high accuracy and good efficiency. Multilayer perceptron neural network (MLP-NN) was introduced to establish the interrelation between the incoming flow conditions and the wake profiles. The Reynolds-averaged Navier-Stokes equations (RANS) are associated with a k − ε turbulence model to offer a number of datasets of wake profile for training, testing, and validation of the MLP-NN models. It was found that the MLP–NN–based model has achieved a considerably high level of accuracy by comparing it with empirical and numerical models. The reliability of the MLP-NN based model coupled with the wake combination RSS model to predict the resultant wake profile and power output of multiple turbines are also assessed. The techniques significantly enhance the efficiency and accuracy of wake predictions.

Modal analysis of composite nozzle for an optimal design of a tidal current turbine

Monitoring of structural vibrations and operational modal analysis are clearly essential to effectively control structural safety and the operational behavior of tidal current turbines. In order to satisfy industrial requirements, generally related to a mass gain problem, hybridization provides an excellent method to improve the breaking strength of composite materials, while keeping adequate mechanical performance for marine renewable energy applications. In this context, this work aims to study the structural modal analysis of a tidal turbine nozzle and the effect of hybrid materials (carbon/Glass) on the natural frequencies and corresponding mode shapes of the three laminates. The modal analysis was calculated by the Finite Element Method using ABAQUS software. According to the results, the stacking sequence has a considerable impact on the natural frequency of the nozzle. Furthermore, it is also found that the resonance effect does not appear for the three laminates under investigation.

Material Selection for Vertical Axis Tidal Current Turbine using Multiple Attribute Decision Making (MADM)

Marine renewable energy technology has attracted many stakeholders to develop due to its enormous resources and future potential advantages. One of them is the vertical axis tidal current turbine technology, which converts the kinetic energy of flowing seawater to be electrical energy. To operate the vertical axis tidal current turbine, especially its metallic components of the supporting structure, it is required to endure the aggressive and corrosive marine environment. Thus, deciding the good and suitable material for this application is very important in order to reduce the risk and hazards from the sea environment. The purpose of this paper is to decide the best metal material for the support structure of the vertical axis tidal current turbine. Therefore, the material candidate and their properties were firstly reviewed and discussed. Then, the material selection was processed through Multiple Attribute Decision Making (MADM) and formulated via the method of a Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS). The result of material selection was carbon steel AISI 1045 as the selected material instead of other candidates such as carbon steel AISI 1018, stainless steel, and nickel aluminium bronze. Thus, it is expected to perform well to be used for the support structure and endure the marine hazards during the vertical axis tidal current turbine application.

Harnesssing Technology Maintenance Process of Tidal Energy Converter

Tidal energy has become an alternative solution for energy source in the future especially for countries with vast ocean such as Indonesia. Tidal energy converter is relatively new which resulted in different concept or even prototypes. The design of tidal energy converter must consider the simplicity of the maintenance process. How is the existing prototypes of tida energy converter maintenance process. This paper evaluate the existing prototype which use floating platform such as Larantuka strait and Madura strait prototype which use Darrieus turbine, T Files turbine which use gorlov turbine, BlueTEC and Horizontal Axis Tidal Current Turbine (HATCT) which use horizontal turbine. The evaluation are based on several criteria such as operational check, inspection and maintenance of harnessing technology or turbine arm where shaft, gearbox and generator are included in the arm which can be called as harnessing technology. The results of comparison shows that the tilted method of maintenance has advantages of visual inspection. The comparison also shows that there is still room for improvement for the design regarding the onsite maintenance by providing larger deck. As the answer of the comparison, a novel design concept is offered using turbine arm with motor for tilting the arm and larger deck area.

A mixed-integer programming methodology to design tidal current farms integrating both cost and benefits: A case study in the Chacao Channel, Chile

In a tidal power plant the most important devices are the tidal current turbines that harvest the kinetic energy contained in the tide and convert it into electricity. The number of turbines to install, their spatial configuration, and the connection of submarine cables are critical aspects in the development of marine energy projects. Here, we present a mixed-integer programming methodology to design tidal current farms considering both cost and benefits. We propose a model that solves, concurrently, the turbine’s locations and cable infrastructure by computing the number, locations, submarine connections of tidal turbines, and the tidal current farm’s overall capacity. The proposed model considers location-based costs, including cable routing and loss from wake effect and electrical transmission, to maximize the project’s economic viability. We demonstrate the methodology’s utility by determining the optimal turbines’ configuration in a real-life case study in the Chacao Chanel, Chile. Finally, practitioners can easily implement our methodology using any standard off-the-shelf mixed-integer programming software to evaluate their tidal current farm projects.

Research method for hydrodynamic characteristics of tidal current turbine

Tidal energy is a very rich Marine resource, which has high energy concentration, small geometric scale and strong predictability. The research status, development and utilization of tidal current turbine at home and abroad are expatiated, and two research methods for hydrodynamic characteristics of tidal current turbine, including numerical calculation and simulation experiment, are introduced, which are of certain significance to the performance optimization of tidal current turbine.

Optimal layout of a Co-Located wind/tidal current farm considering forbidden zones

Co-location of wind and tidal current turbines (WTs/TCTs) is a new way to improve the economy and reliability of electricity generation from renewable energy sources. In this paper, an optimization model for determining the configuration of a co-located wind/tidal current farm (WF/TCF) is proposed. The objectives include the minimization of the system levelized cost of energy (LCOE) and the maximization of the system average power supply reliability (APSR). In the planning area, there are certain zones where there are important restrictions which do not allow WTs/TCTs to be installed. These are called forbidden zones. When deciding the feasible area in the optimization, the complement of the forbidden zones in the planning area is used. The optimization problem is formulated as a coordinate model (CM) and a grid model (GM), both solved by the multi-swarm optimization (MSO) algorithm. The proposed approach is tested in an offshore area of Zhejiang province, China. Simulation results indicate that the co-location of a WF/TCF is an economic-technical efficient approach to harvest marine renewable energy. Also, the MSO algorithm outperforms its counterparts, the particle swarm optimization (PSO) and the discrete particle swarm optimization (DPSO) algorithms, in solving the CM and the GM of the WF/TCF layout optimization problem.

Spatial evolution and kinetic energy restoration in the wake zone behind a tidal turbine: An experimental study

In the case of tidal turbine arrays, the spatial evolution pattern of turbine wakes affects the power performance of other turbines and the hydrodynamic environment of adjacent turbines. However, the evolution mechanism is unclear, particularly in terms of wake energy restoration process. Therefore, we investigated the wake spatial evolution mechanism of a tidal current turbine experimentally. The experiment used a porous disc to simulate the turbine rotor based on the equivalence principle of force. An acoustic Doppler velocimeter and a strain gauge measured the time-varying velocities and flow loads, respectively. The momentum loss generated a wake zone in the downstream with enhanced turbulence originating from the boundary shear layer. Initially, the velocity deficit in the wake core increased as the shear layer spread inwards. Moreover, the disc blockage accelerated the flow, generating high momentum transported into the wake zone. However, the wake expansion and turbulence dissipation were limited until the shear-induced turbulence appeared at the wake centre. The kinetic energy in the wake region recovered significantly in the range x = (2D, 3D). As the wake moved downstream, further energy restoration was observed in the entire wake region. However, the rate of energy transformation decreased beyond 7D downstream.

Investigation of wave–current interaction for a tidal current turbine

Due to linear wave theory limitations, higher-order theories have been coupled with the Blade Element Momentum (BEM) model to predict the time behavior of the dynamic loading on the combined wave–current field. Second-order, third-order approximations and fifth-order stokes theory have been used to check their effects on the predicted wave kinematics and on the resulting dynamic loadings. To overcome the problem of linear superposition method, a wave–current interaction model was implemented. A significant change in the wave length and wave height was obtained, whereas a negligible change was observed for the current velocity and water depth. By implementing a wave–current interaction model for a wave train and inflow current in the same direction of the wave propagation, the loading ranges of blade root bending moments significantly decreased, whereas their wave lengths increased. Furthermore, a parametric study was performed through increasing the wave height and current velocity to reveal their effects on the dynamic loadings with and without considering the wave–current interaction. Big differences were obtained between the maximum predicted loads for cases with and without interaction, which would help in the proper selection of tidal current turbine’s structural design.

ALM과 LES를 이용한 조류발전터빈의 유체 성능과 후류 분석

ALM과 LES를 이용한 조류발전터빈의 유체 성능과 후류 분석

Effect of a Support Tower on the Performance and Wake of a Tidal Current Turbine

Tidal energy is one of the major sources of renewable energy. To accelerate the development of tidal energy, improved designs of Tidal Current Turbine (TCT) are necessary. The effect of tower on performance and wake of TCT is investigated using Computational Fluid Dynamics (CFD) simulations. Transient analysis with transient rotor stator frame change model and shear stress transport turbulence model are utilized in ANSYS CFX. An experimentally validated numerical model with full scale tidal turbine with a blockage ratio of 14.27% and Tip Speed Ratio (TSR) 4.87 is used to simulate the effect of different tower diameters on performance and wake. The effect of different tower diameters is quantified in terms of coefficient of performance (CP). Coefficient of performance for a 3.5 m tower diameter is 0.472 which is followed by 3, 2.5 and 2 m with coefficients of performance of 0.476, 0.478 and 0.476 respectively. Similarly, the coefficient of thrust (CT) on the rotor for 3.5 m tower diameter is 0.902, for 3 m diameter 0.906 and for 2.5 and 2 m diameters are 0.908 and 0.906 respectively.