Horizontal Axis Tidal Current Turbine Research Articles

Numerical analysis of the hydrodynamic performance and wake field of a horizontal axis tidal current turbine using an actuator surface model

An actuator surface model was used to numerically simulate a tidal turbine, reducing the required number of model grid cells and improving the accuracy of the tidal current turbine wake flow field. In addition, detailed distributions of the body force along the hydrofoil chords were included in the actuator surface model. Next, the hydrodynamic performance and the characteristics of the near and far wake profiles that were predicted using the improved model were compared with the reference models and experimental data, and a good correlation was observed. In this research, the point at which the wake split into the near and the far wake field was between 1/2 and 1 times the diameter of the turbine downstream of the rotor. The axis structure of a tidal current turbine and the gap between the axis and the root of a blade strongly influence the wake profile. In a near wake, the velocity fluctuant shows a greater range of influence along the span-wise direction of the blade. In addition, numerical simulations of the field around blade showed that when the distance to the airfoil was greater than approximately one chord length, the streamlines and pressure contours obtained from the actuator surface model were in good agreement with the streamlines and pressure contours obtained from the reference model.

Performance and Cavitation Analysis on Tidal Current Turbine for Low Water Level Channel

Most tidal current turbine designs are focused on medium and large scale for deep sea, less attention is paid in low water level channel, such as the region around the islands and costal sea. This study is to develop a horizontal axis tidal current turbine rotor blade which is applicable to low water level island region in southwest coastal region of Korea. In this study, the hydrofoil NACA63-415 and NACA63-817 are both adopted to analyze. The blade using NACA63-817 showed the higher maximum power coefficient and good performance at small TSR (Tip Speed Ratio), which gives the blade more advantages in operating at lower water level channel, where is characterized by the fast-flowing water. The cavitation pattern of hydrofoil is predicted by the CFD analysis and verified that the NACA63-817 is the appropriate hydrofoil in the test site of tidal current resource and the hydrofoil showed considerable performance in avoiding cavitation.

The effects of surge motion of the floating platform on hydrodynamics performance of horizontal-axis tidal current turbine

Under practical operation conditions, hydrodynamic characteristics of floating horizontal-axis turbine are affected by the wave-induced motion response of the floating platform for the turbine system. In this thesis, CFX software is adopted to analyze the hydrodynamic performance of the turbine in constant inflow with the turbine being forced vibrating and to study how the hydrodynamic performance of the turbine is influenced by surge frequency, surge amplitude and speed ratio. Based on the simulation data from CFX, axial damping coefficient can be obtained by least square fitting the time-varying axial force curves of surging turbine. The simulation results demonstrate that compared with turbine only rotating in constant inflow, shaft loads and energy utilization ratio of the surging turbine experience oscillations respectively; the oscillation amplitudes of these two parameters have a positive correlation with the frequency and amplitude of the surge and speed ratio; the frequency and amplitude of the surge have little impact on axial damping coefficient but this coefficient is positively proportioned to the rotational speed of the turbine. The results of this study can provide data to study motion response of floating platform for floating tidal current turbine system and control design of the output electricity.

Shape design and numerical analysis on a 1 MW tidal current turbine for the south-western coast of Korea

The study concentrates on the shape design and numerical analysis of a 1 MW horizontal axis tidal current turbine (HATCT), which can be applied near the southwest regions of Korea. On the basis of actual tidal current conditions of south-western region of Korea, configuration design of 1 MW class turbine rotor blade is carried out by blade element momentum theory (BEMT). The hydrodynamic performance including the lift and drag forces, is conducted with the variation of the angle of attack using an open source code of X-Foil. The optimized blade geometry is used for Computational Fluid Dynamics (CFD) analysis with hexahedral numerical grids. This study focuses on developing a new hydrofoil and designing a blade with relatively shorter chord length in contrast to a typical TCT blade. Therefore, after a thorough study of two common hydrofoils, (S814 and DU-91-W2-250, which show good performance for rough conditions), a new hydrofoil, MNU26, is developed. The new hydrofoil has a 26% thickness that can be applied throughout the blade length, giving good structural strength. Power coefficient, pressure and velocity distributions are investigated according to Tip Speed Ratio by CFD analysis. As cavitation analysis is also an important part of the study, it is investigated for all the three hydrofoils. Due to the shorter chord length of the new turbine blade in contrast to a typical TCT blade design, a Fluid Structure Interaction (FSI) analysis is also done. Concrete conclusions have been made after comparing the three hydrofoils, considering their performance, efficiency, occurrence of cavitation and structural feasibility.

Design and Study on Ocean Energy with the Horizontal Axis Tidal Current Turbine's Blade Especially for China's Low Tidal Current Velocity

Tidal current energy of sea surface is a kind of renewable energy with wide prospect of development. Because of its relatively high utilization ratio, the horizontal-axis turbine generation system utilizing tidal current energy has become the focus of technology development of tidal current energy all over the world. In this paper, the authors analyze the characteristics of surface tidal current energy along the coast of China. Meanwhile, we use BEM mathematical model to design the 2.5kW Horizontal Axis Tidal Current Energy Turbine Generator Blade, which is suitable for the features of tidal current energy in our country. The result of the prototypes dragging experiment indicates that this design method has good application value.

Equations used to predict the velocity distribution within a wake from a horizontal-axis tidal-current turbine

The investigation of the wake from a tidal-current turbine becomes important when considering a tidal farm. Each single turbine wake in a turbine farm would significantly affect the performance of another turbine located adjacent or downstream. In this study, two novel analytical equations are developed to predict the mean velocity within the wake of a tidal-current turbine. The equations are proposed to predict the initial velocity close to the turbine and the lateral distributions at various sections downstream, respectively. The first equation for the initial flow prediction is derived based on the axial momentum theory and dimensional analysis, while the second equation for lateral velocity distribution prediction is derived based on Gaussian probability distribution. The derivation of the proposed equations is presented and their predictions are compared with the existing experimental and numerical results. Validation of these novel equations gives a variation of 6% at the initial flow and 8% at the lateral sections compared to the experimental and numerical results. These equations are potentially the foundation of the analytical method for wake prediction of a tidal turbine.

Blade design and performance analysis on the horizontal axis tidal current turbine for low water level channel

Most tidal current turbine design are focused on middle and large scale for deep sea, less attention was paid in low water level channel, such as the region around the islands, coastal seas and rivers. This study aims to develop a horizontal axis tidal current turbine rotor blade which is applicable to low water level island region in southwest of Korea. The blade design is made by using BEMT(blade element momentum theory). The section airfoil profile of NACA63-415 is used, which shows good performance of lift coefficient and drag coefficient. Power coefficient, pressure and velocity distributions are investigated according to TSR by CFD analysis.

Shape design and CFD analysis on a 1MW-class horizontal axis tidal current turbine blade

This study aims to develop a 1MW-class horizontal axis tidal current turbine rotor blade which can be applied near the southwest island regions of South Korea. On the basis of actual tidal current conditions of southern region of Korea, configuration design of 1MW class turbine rotor blade is carried out by BEMT (Blade element momentum theory). The hydrodynamic performance including the lift and drag forces, is conducted with the variation of the angle of attack using an open source code of X-Foil. The purpose of the study is to study the shape of the hydrofoil used and how it affects the performance of the turbine. After a thorough study of many airfoils, a new hydrofoil is developed using the S814 and DU-91-W2- 250 airfoils, which show good performance for rough conditions. A combination of the upper and lower surface of the two hydrofoils is tested. Three dimensional models were developed and the optimized blade geometry is used for CFD (Computational Fluid Dynamics) analysis with hexahedral numerical grids. Power coefficient, pressure coefficient and velocity distributions are investigated according to Tip Speed Ratio by CFD analysis.

Performance analysis of a HAT tidal current turbine and wake flow characteristics

Having very strong current on the west coast with up to 10 m tidal range, there are many suitable sites for the application of tidal current power (TCP) in Korea. The turbine, which initially converts the tidal energy, is an important component because it affects the efficiency of the entire system. To design a turbine that can extract the maximum power on the site, the depth and duration of current velocity with respect to direction should be considered. To extract a significant quantity of power, a tidal current farm with a multi-arrangement is necessary in the ocean. The interactions between devices contribute significantly to the total power capacity. Thus, the study of wake propagation is necessary to understand the evolution of the wake behind a turbine. This paper introduces configuration design of horizontal axis tidal current turbine based on the blade element theory, and evaluating its performance with CFD. The maximum efficiency of the designed turbine was calculated as 40% at a tip speed ratio (TSR) of 5. The target capacity of 300 kW was generated at the design velocity, and the performance was stable over a wide range of rotating speeds. To investigate the wakes behind the turbine, unsteady simulation was carried out. The wake velocity distribution was obtained, and velocity deficit was calculated. A large and rapid recovery was observed from 2D to 8D downstream, followed by a much slower recovery beyond. The velocity was recovered up to 86% at 18D downstream.

Design of a horizontal axis tidal current turbine

Pacific Island Countries (PICs) have a huge renewable energy potential to meet their energy needs. Limited resources are available on land; however, large amount of ocean energy is available and can be exploited for power generation. PICs have more sea-area than land-area. Tidal current energy is very predictable and large amount of tidal current energy can be extracted using tidal current energy converters. A 10m diameter, 3-bladed horizontal axis tidal current turbine (HATCT) is designed in this work. Hydrofoils were designed for different blade location; they are named as HF10XX. The hydrodynamic characteristics of the hydrofoils were analyzed. A thick hydrofoil with a maximum thickness of 24% and a maximum camber of 10% was designed for the root region. The maximum thickness of hydrofoils was varied linearly from the root to the tip for easier surface merging. For the tip region, a thinner hydrofoil of maximum thickness 16% and maximum chamber 10% was designed. It was ensured that the designed hydrofoils do not experience cavitation during the expected operating conditions. The characteristics of the HF10XX hydrofoils were compared with other commonly used hydrofoils. The blade chord and twist distributions were optimized using BEM theory. The theoretical power output and the efficiency of the rotor were also obtained. The maximum power at the rated current of 2m/s is 150kW and the maximum efficiency is 47.5%. The designed rotor is found to have good efficiency at current speeds of 1–3m/s. This rotor has better performance than some other rotors designed for HATCT.

Numerical investigations of the effects of different arrays on power extractions of horizontal axis tidal current turbines

As the tidal current industry grows, power extraction from tidal sites has received widespread attention. In this paper, a blade element actuator disk model that is coupled with the blade element method and a three-dimensional Navier–Stokes code is developed to analyse the relationship between power extraction and the layout of turbine arrays. First, a numerical model is constructed to simulate an isolated turbine and the model is validated using experimental data. Then, using this validated model, the power extraction of horizontal axis tidal current turbines using different tidal turbine arrays and rotation directions is predicted. The results of this study demonstrate that staggered grid array turbines can absorb more power from tidal flows than can rectilinear grid array turbines and that staggered grid array turbines are less affected by the rotation of upstream turbines. In addition, for staggered gird arrays, the relationships between power coefficients, lateral distance and longitudinal distance are discussed. The appropriate lateral distance is approximately 2.5 turbine diameters, whereas for the longitudinal distance, the largest value possible should be used. The relative power coefficient can achieve 3.74 when the longitudinal distance is 6 times the turbine diameter. To further increase the power extraction, this study suggests an improved staggered grid array layout. The relative power coefficient of the improved four-row turbine arrays is approximately 3–4% higher than that of the original arrays and will increase as the distance between the second-row and third-row increases. Considering only the first two rows of turbines, the total power extraction can be 11% higher than for an equivalent number of isolated turbines.

조류발전 시스템용 쉬라우드의 형상각도별 일정 조류속도장 내 해수유동 특성연구

수평축 조류발전 시스템에 사용되는 쉬라우드의 기하학적 형상각도별 해수의 유동장 특성을 전산유체역학을 통해 분석하였다. 쉬라우드를 포함한 전체 유동장 내 해수의 유속 분포는 일정한 조류속도조건에서 쉬라우드의 형상에 따라 크게 영향을 받으며 특히 발전성능에 직접적으로 영향을 미치는 쉬라우드 내 최대유속의 위치 및 크기는 형상 별로 큰 차이가 있다. 실린더와 디퓨저부분의 길이가 같은 실린더-디퓨저 형태의 쉬라우드에서는 실린더 영역에서 비교적 높은 유속분포가 형성되었으며 노즐과 디퓨저부분의 길이가 같은 대칭구조의 노즐-디퓨저에서는 내경이 최소인 지점에서 국부적으로 나타났다. 실린더-디퓨저 쉬라우드에서 조류속도에 비해 높은 유속이 형성되었으며 중심축상의 유속은 노즐-디퓨저와는 다르게 쉬라우드 입구 근처에서 점차 증가하기 시작하여 실린더부분의 중앙 부근에서 피크값을 지나 디퓨저에서 급격히 감소한 후 다시 일정한 속도로 유지되어 가는 특성을 나타내었다. 이러한 쉬라우드의 형상과 해수유동장 변화특성에 대한 분석결과는 효율적인 조류발전시스템을 위한 쉬라우드의 최적설계에 응용될 수 있을 것으로 기대된다. Numerical analyses through Computational Fluid Dynamics have been performed to investigate the seawater flow field characteristics for various shrouds used in horizontal axis tidal current turbine systems. Seawater flow characteristics are largely influenced under constant tidal current velocity by the shroud geometry and there is considerable difference in fluid velocity distributions around the shrouds. Especially the location and magnitude of maximum seawater flow velocity directly affect turbine performance for power generation. For the cylinder-diffuser type shroud system whose cylinder and diffuser parts have the same length accelerated flow region is formed in the overall cylinder part while maximum velocity in the nozzle-diffuser type whose nozzle and diffuser parts have the same length with symmetry, locally appears near the minimum sectional area. In case of cylinder-diffuser type shroud fluid velocity increases rather high compared with current velocity. And fluid velocity at the centerline gradually increases from the entrance, and then decreases rapidly after reaching a peak close to the middle of the cylinder part unlike the nozzle-diffuser while there is not much variation near the rear of the shroud. These results of the seawater flow characteristics with various shroud geometries can be applied to optimal design for the development of efficient tidal current power generation systems.

조류발전용 수평축 터빈의 형상설계 및 가변 부하를 이용한 성능실험

Due to a high tidal range of up to 10 m on the west coast of Korea, numerous tidal current projects are being planned and constructed. The turbine, which initially converts the tidal energy, is an important component because it affects the efficiency of the entire system. Its performance is determined by design variables such as the number of blades, the shape of foils, and the size of a hub. To design a turbine that can extract the maximum power on the site, the depth and duration of current velocity with respect to direction should be considered. Verifying the performance of a designed turbine is important, and requires a circulating water channel (CWC) facility. A physical model for the performance test of the turbine should be carefully designed and compared to results from computational fluid dynamics (CFD) analysis. In this study, a horizontal axis tidal current turbine is designed based on the blade element theory. The proposed turbine's performance is evaluated using both CFD and a CWC experiment. The sealing system, power train, measuring devices, and generator are arranged in a nacelle, and the complete TCP system is demonstrated in a laboratory scale. Tidal current power(TCP: 조류발전), Turbine(터빈), Blade element theory(날개요소이론), Computational fluid dynamics (CFD: 전산유체역학), Circulating water channel(CWC: 회류수조), Renewable energy(신재생에너지)

Blade sections for wind turbine and tidal current turbine applications-current status and future challenges

The designers of horizontal axis wind turbines and tidal current turbines are increasingly focusing their attention on the design of blade sections appropriate for specific applications. In modern large wind turbines, the blade tip is designed using a thin airfoil for high lift : drag ratio, and the root region is designed using a thick version of the same airfoil for structural support. A high lift to drag ratio is a generally accepted requirement; however, although a reduction in the drag coefficient directly contributes to a higher aerodynamic efficiency, an increase in the lift coefficient does not have a significant contribution to the torque, as it is only a small component of lift that increases the tangential force while the larger component increases the thrust, necessitating an optimization. An airfoil with a curvature close to the leading edge that contributes more to the rotation will be a good choice; however, it is still a challenge to design such an airfoil. The design of special purpose airfoils started with LS and SERI airfoils, which are followed by many series of airfoils, including the new CAS airfoils. After nearly two decades of extensive research, a number of airfoils are available; however, majority of them are thick airfoils as the strength is still a major concern. Many of these still show deterioration in performance with leading edge contamination. Similarly, a change in the freestream turbulence level affects the performance of the blade. A number of active and passive flow control devices have been proposed and tested to improve the performance of blades/turbines. The structural requirements for tidal current turbines tend to lead to thicker sections, particularly near the root, which will cause a higher drag coefficient. A bigger challenge in the design of blades for these turbines is to avoid cavitation (which also leads to thicker sections) and still obtain an acceptably high lift coefficient. Another challenge for the designers is to design blades that give consistent output at varying flow conditions with a simple control system. The performance of a rotating blade may be significantly different from a non-rotating blade, which requires that the design process should continue till the blade is tested under different operating conditions. Copyright © 2012 John Wiley & Sons, Ltd.

An experimental survey in the wake of a simulated tidal current turbine

This paper presents two experimental test programmes, conducted in a water flow channel and a tow tank respectively, and devised to investigate the wake behind a simulated horizontal axis tidal current turbine. Both sets of experimental results have identified the wake as having a Gaussian-like shape and the wake deficit recovering gradually with distance downstream. Also, although it is not directly representative of real operating conditions, the appropriateness of a towing tank for the model tidal current turbine testing has been supported, by having obtained compatible force and wake profiles in the two test programmes