Horizontal Axis Tidal Current Turbine Research Articles

Numerical Investigation on Hydrodynamic Performance of a Horizontal Axis Tidal Current Turbine

Numerical Investigation on Hydrodynamic Performance of a Horizontal Axis Tidal Current Turbine

A parametric analysis of the performance of a horizontal axis tidal current turbine for improving flow-converging effect

This paper proposed a research method for secondary design and parametric analysis of the contraction section of the shroud to improve the flow-gathering effect of horizontal axis tidal current turbines. By comparing the velocity ratio, drag coefficient, and flow field stability of the nine different shroud profile types, a conclusion was drawn that the hydrodynamic performance of the exponential (Type-A) shroud is best. On this basis, the primary parametric analysis of the A profile type shroud is carried out by changing the contraction ratio of the shroud's contraction section to divide the profile into three parts. The results show that the vertical flange inhibits the flow-gathering effect of the shroud, so the secondary parametric analysis is proceeded by removing the flange and changing the flange inclination angle, respectively. At the contraction ratio of 6/8, the flow-gathering effect of each shroud is best, among which the hydrodynamic performance of Type-ABL-6-85° shroud with the flange inclination angle of 85° is best. The maximum power coefficient (Cpmax) is 43.20%, which is 31.59% higher than that with Type-A shroud when the tip speed ratio is 1.5. Therefore, it can be considered that the combined profile type of the shroud contraction section has a better flow-gathering effect than the single profile type.

Blade optimization for hydrodynamic performance improvement of a horizontal axis tidal current turbine

This paper proposes an innovative methodology applied to blade optimization for hydrodynamic performance improvement of a horizontal axial tidal current turbine (HATCT) considering the effect of Reynolds number. Axial induction factor, tangential induction factor and angle of attack are employed for identifying the accuracy and applicability of modified Blade Element Momentum (BEM) theory. Combined with the XFoil software, the hydrofoil shape function is represented by trigonometric functions through Theodorsen method. The hydrodynamic characteristics of the hydrofoil are employed as the optimization targets, and the particle swarm optimization algorithm is used to optimize the original hydrofoil. Based on the modified BEM theory and the optimized hydrofoil, the tidal current turbine power coefficient at different tip speed ratio (TSR) is optimized according to the MATLAB function. The optimized tidal current turbine shows better performance compared with the original tidal current turbine.

Hydrodynamics and Wake Flow Analysis of a Floating Twin-Rotor Horizontal Axis Tidal Current Turbine in Roll Motion

The study of hydrodynamic characteristics of floating double-rotor horizontal axis tidal current turbines (FDHATTs) is of great significance for the development of tidal current energy. In this paper, the effect of roll motion on a FDHATT is investigated using the Computational Fluid Dynamics (CFD) method. The analysis was conducted in the CFD software STAR-CCM+ using the Reynolds-averaged Navier–Stokes method. The effects of different roll periods and tip speed ratios on the power coefficient and thrust coefficient of FDHATT were studied, and then the changes in the vorticity field and velocity field of the turbine wake were analyzed by two-dimensional cross-section and Q criterion. The study indicates that roll motion results in a maximum decrease of 30.76% in the average power coefficient and introduces fluctuations in the instantaneous load. Furthermore, roll motion significantly accelerates the recovery of wake velocity. Different combinations of roll periods and tip speed ratios lead to varying degrees of wake velocity recovery. In the optimal combination, at a position 12 times the rotor diameter downstream, roll motion can recover the wake velocity to 92% of the incoming flow velocity. This represents a 23% improvement compared to the case with no roll motion.

Experimental study of the turbulent flow in the wake of a horizontal axis tidal current turbine

A scaled-model of a horizontal axis tidal current turbine (HATCT) is tested in the CNR-INM Circulating Water Channel. The experiments are designed to establish in the first place the performances of the turbine at different working settings. The second goal is to investigate the hydrodynamics generated by the turbine in the near wake using the Particle Image Velocimetry (PIV) technique. For this purpose, velocity measurements are performed in a longitudinal plane and phase-locked to the rotor angle in order to resolve the wake structure at different working regimes. The analysis of the axial and radial velocity fields reveals the flow features of the slipstream, as well as its expansion and dependence on the turbine operating parameters. Analysis of the non-diagonal terms of the Reynolds stress tensor provides insight into the onset of tip vortex pairing and of vortex instabilities. Furthermore the separate contributions of transport, production and dissipation to the turbulent kinetic energy in the wake field are discussed in detail. The vortex unsteadiness is captured and correlated with the evolution of the kinetic energy transport and production terms. Understanding these phenomenologies is an important step to develop computational tools able to estimate the radiated noise or the potential impact of turbulence on performances of further rotors placed in the wake, as in an array of tidal turbines.

Study on fast prediction method of hydrodynamic load of floating horizontal axis tidal current turbine with pitching motion under free surface

The floating horizontal-axis tidal current turbine (HATCT) moves with the floating carrier while rotating, resulting in a change in its relative inflow velocity at any time. If the rotating speed of the HATCT is fixed, the HATCT cannot work at the optimum tip speed ratio, resulting in the failure to achieve the optimum power generation efficiency. Therefore, this paper proposes a control strategy for the rotating speed of the HATCT, and obtains the hydrodynamic loads of the HATCT with variable speed rotation and pitching motion under free surface conditions based on the CFD method. Compared with the hydrodynamic load of the HATCT under the same situation but with fixed speed control, the variable speed control can effectively improve the power coefficient of the HATCT, but the load fluctuation in terms of the inflow direction load, power, and pitch moment coefficients are more significant than those with fixed speed control. On this basis, according to the variation law of the damping coefficient with pitch period, pitch amplitude, and tip speed ratio, the hydrodynamic load prediction method of the HATCT with pitching motion is established. The validity of this prediction method is verified by comparing the results with those of CFD calculation.

Research on an All-Flow Velocity Control Strategy for a 120 kW Variable-Pitch Horizontal Axis Tidal Current Turbine

Horizontal-axis tidal current turbines have considerable potential to harvest renewable energy from ocean tides. The pitch control system is a critical part of variable-pitch tidal turbines. Existing control strategies for tidal turbines mainly rely on flow measurement devices to obtain tidal velocities, which are costly and subject to many limitations in practical applications, making them unsuitable for small off-grid tidal turbines. In this paper, we propose a pitch control strategy for a 120 kW horizontal-axis tidal current turbine based on the output power of the generator. The torque of the turbine was calculated based on the blade element momentum theory, and a dynamic model of the tidal turbine was established. The dynamic characteristics of the turbine and generator were studied under various flow rates and pitch angles. On the basis of the characteristic analysis, the generating efficiency of the unit was improved under a low flow rate, and the output power was limited to a rated value under high-current velocity by regulating the pitch angle. Furthermore, a novel protection and start up strategy is proposed to protect the unit and make full use of the tidal energy when the tidal current velocity exceeds the limit value. We performed simulations, the obtained results of which demonstrate the effectiveness and advantages of the designed control strategies.

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.

Dynamics analysis of the power train of 650 kW horizontal-axis tidal current turbine

Power trains are an important component of the tidal current energy conversion systems; however, the variable drive-torque and unbalanced moments produced by flow shear and turbulence cause power trains to vibrate. When the scale of the tidal current turbine increases, the vibration problem becomes prominent. The dynamic characteristics of power trains are complex. In this study, the power train of a 650 kW horizontal-axis tidal current turbine was studied. The power train adopted a low-speed-ratio semi-direct drive scheme proposed by Zhejiang University. A mathematical model of the power train was constructed. The influence of external excitations (including tidal current condition, unbalanced moments, and internal excitation) on dynamic characteristics was studied using simulations and sea trials. The simulation results showed that the radial and torsional vibrations of the low- and the high-speed shafts increased when the tidal current velocity increased. The fluctuation range of the bearing load increased under increases in the pitch and yaw moments. The meshing motion of the planetary gear plays a leading role in the vibration of low- and high-speed shafts. The power train model was validated by comparing the results of the experiment and simulation.

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....

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.

The effects of surge motion on hydrodynamics characteristics of horizontal-axis tidal current turbine under free surface condition

To study the hydrodynamic characteristics of a floating horizontal-axis tidal turbine (HATT) with rotation and surging motion under the condition of the free surface, a numerical simulation method based on CFD is established. The axial load coefficient and energy utilization ratio at different blade tip-immersion depths, surge periods and surge amplitudes were analyzed. The results show that the instantaneous values of the axial load coefficient and energy utilization ratio have obvious periodic fluctuations, and the fluctuation amplitude increases with the increase of the frequency and amplitude of surging. On this basis, the hydrodynamic load is divided into the hydrodynamic load in case of rotation only, the damping force and the additional mass force. The damping and additional mass coefficients are obtained based on the least square method. The damping coefficient of axial load coefficient changes little with the increase of surge frequency and amplitude, but increases with the increase of the blade tip-immersion depth. The damping coefficient of energy utilization ratio fluctuates periodically, and the fluctuation period is equal to the surge period. The research findings can provide relevant data for studying the coupling motion of floating tidal current energy device and control design of the output electricity.

Hydrodynamic study on horizontal-axis tidal current turbine with coupling motions

Hydrodynamic study on horizontal-axis tidal current turbine with coupling motions

Design of the Blade under Low Flow Velocity for Horizontal Axis Tidal Current Turbine

The blade is the key component for energy capture in horizontal axis tidal current turbine, and the blade’s design is directly related to the efficiency of the power generation device. The seawater flow velocity is a crucial parameter for blade design. Since the seawater velocity changes constantly, it is extremely important to determine the design velocity of the blade. This article proposes a calculation method for the design velocity of the blade so that the designed blade can achieve better energy collection efficiency under a variable flow velocity. This study performed the following investigations: (1) The author tested and analyzed the seawater velocity variation at the experimental site, determining the designed flow velocity via calculations; (2) The author combined the blade element momentum and Wilson’s optimization design method using the MATLAB software to calculate the blade shape parameters and predict the performance under a number of different flow velocity forecasts; (3) When testing the device under sea conditions, the experimental results showed that the performance capture devices and digital projections are basically the same, which verifies the validity and effectiveness of the design method.

Hydrodynamic Analysis of Horizontal Axis Tidal Current Turbine under the Wave-Current Condition

To take advantage of the high tidal current velocity near the free surface, the horizontal axis turbine is installed, which inevitably causes hydrodynamic characteristics to effect the turbine by the waves. In this article, we established a numerical calculation method for the hydrodynamic load of a horizontal axis turbine under wave-current conditions. Based on the numerical calculation results, the hydrodynamic loads were decomposed and the influence rules of wave parameters and blade tip immersion depth on the hydrodynamic load were obtained. The study found the following: (1) the multi-frequency fluctuations based on the rotation frequency and incident wave frequency occurred in instantaneous values of the axial load coefficients and energy utilization ratios, and the fluctuation amplitude decreased with the increase of the blade tip immersion depth; (2) the fluctuation amplitude, according to rotation frequency, changed less with the increase of wave period and wave height, and was smaller according to wave frequency; (3) the fluctuation amplitude based on wave frequency increased linearly with the increase of wave height and wave period. The research results can provide the basis and reference for the design and engineering application of tidal current power station.

Load reduction for two-bladed horizontal-axis tidal current turbines based on individual pitch control

With the large progress in tidal current energy, the size of tidal current turbine (TCT) rotors has increased, leading to more substantial asymmetrical loads. In this study, severe asymmetrical loads were investigated by a sea trial experiment with a 600-kW two-bladed horizontal-axis TCT. Individual pitch control (IPC) has been recommended and validated to be effective for load reductions. Each blade is individually and actively controlled during IPC to compensate for asymmetrical loads within the rotational cycle. IPC has significant engineering implications but may cause partial energy loss under below-rated conditions. However, the conventional IPC method has limitations for two-bladed turbines. Thus, to alleviate the fatigue loads of two-bladed TCTs, a new IPC method based on vector analysis is presented in this paper. An integral sliding mode controller is designed for the proposed IPC to eliminate the phase lag resulting from the signal filter and actuator. To validate the feasibility and investigate the performance of the proposed sliding mode control (SMC) strategy, a collaborative simulation using GH-Bladed and Simulink was carried out. The comparative simulation results demonstrated the feasibility of the proposed IPC method and the better performance of the proposed SMC controller compared with a conventional PI controller.

Research on Pitch Control Strategies of Horizontal Axis Tidal Current Turbine

Based on blade element momentum theory and generator characteristic test, a dynamic simulation model of 150 kW horizontal-axis tidal current turbine was established. The matching of the dynamic characteristics between the turbine and generator under various current velocities is studied, and the influence of the pitch angle on the matching is analyzed. For the problem of maximum power output in case of low current speed and limiting power in high current speed, the relation between optimal pitch angle and output power is analyzed. On the basis of dynamic characteristic analysis, the variable pitch control strategy is developed. The performance of the turbine under various tidal conditions is simulated. The research results show that the designed controller enables the turbine to operate efficiently under the condition of low current speed, and achieve the goal of limited power at high current speed.

Investigation of parameters affecting horizontal axis tidal current turbines modeling by blade element momentum theory

The Blade Element Momentum Theory (BEMT) is one of the most common and widely used methods in horizontal axis wind and tidal turbine performance prediction. It mainly relies on two-dimensional (2-D) hydrodynamic, lift and drag, coefficients which are used to calculate the hydrodynamic forces within the blade element section of the model. These coefficients are greatly affected by both Reynolds numbers and turbulence transition parameter (Ncrit). The performance sensitivity of scale models tidal current turbines (TCTs) to the change of Reynolds numbers and Ncrit parameter was assessed. Initially, the BEMT was validated with experimental measurements of two scale models of horizontal axis tidal current turbines. A very good agreement was seen, thus, confidence in both the implementation of the theory and the applicability of the method was built up. Lift and drag coefficients were calculated from XFoil through the use of different sets of Reynolds numbers at different Ncrit values. The best BEMT validations with experimental data were seen when the hydrodynamic coefficients were calculated at two sets of Reynolds numbers considered at optimal performance. The first set was calculated at 75% of the blade span while the second set was calculated at every local elemental position of the blade. For facilitation, reduction of time and effort, Reynolds numbers at 75% of the blade span is considered the best choice. Furthermore, the BEMT model results showed better agreements with experimental data when lift and drag coefficients were calculated at low values of Ncrit parameter. The predicted tidal turbine performances of previous experimental data by the present BEM model were compared with those derived from the academic SERG-Tidal BEM code. The present BEM model, based on the proper selection of both Reynolds number and Ncrit parameter, showed an obvious superiority over SERG-Tidal model.

Indirect load measurements for large floating horizontal-axis tidal current turbines

Tidal current turbines have undergone tremendous development on their scales and capacities in recent decades, but their further commercial application has encountered great challenges, including their high energy cost and short lifetime. The optimization design for cost reduction requires accurate and reliable turbine load information, and the load reduction control for life extension requires recognizable real-time fatigue load feedback. To avoid the difficulty and complication of direct load measurements, an indirect load measurement method for a large floating horizontal-axis tidal current turbine was proposed in this study based on the numerical relationship between the turbine loads and platform responses. The operation principle of the proposed method was defined in detail, and a turbine load measurement system was designed. To validate the feasibility of this measurement system, a measurement experiment for a 300-kW tidal current turbine on a floating platform was conducted. The turbine loads, consisting of the turbine thrust and fatigue loads, were estimated based on the measured information. In a comparison with the load information predicted by software simulation, good agreement, especially on the turbine thrust, was obtained. The estimated fatigue load signal indicated a high signal-to-noise ratio, which can provide reliable support for load control.