Vertical Axis Marine Current Turbines Research Articles

Study of Vortex Effect on Vertical Axis Marine Current Turbine Arm

The design of a marine current turbine generator specifically in deep water with unequal seabed which requires the designer to develop a floating platform for the turbine. It creates a massive challenge in improving the mechanical system, such as the turbine arm. In order to make the monitoring and maintenance accessible, the generator must be placed on the platform’s deck. A long shaft is required to make the connection between the generator and turbine. The problems occur due to the vibration generated by the vortex around the shaft or the turbine arm. This paper aim is to investigate the vortex effect on the turbine arm and propose an advanced design to reduce its impact. The computational fluid dynamic method is approached to analyse the vortex generated by the turbine arm. The analysis compared the conventional cylindrical and the foil-shaped turbine arm. Moreover, the investigation includes force along the X-axis and Y-axis, flow, drag, lift coefficient, also fatigue lift near the turbine arm. The numerical output illustrates that the foil shaped on the turbine arm provided limited vortex and improved the performance compared to the conventional cylindrical turbine arm.

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.

Influences of Geometrical Parameters of Upstream Deflector on Performance of a H-Type Vertical Axis Marine Current Turbine

Marine current power is a kind of renewable energy that has attracted increasing attention because of its abundant reserves, high predictability, and consistency. A marine current turbine is a large rotating device that converts the kinetic energy of the marine current into mechanical energy. As a straight-bladed vertical axis marine current turbine (VAMCT) has a square or rectangular cross-section, it can thus have a larger swept area than that of horizontal axis marine current turbines (HAMCT) for a given diameter, and also have good adaptability in shallow water where the turbine size is limited by both width and depth of a channel. However, the low energy utilization efficiency of the VAMCT is the main bottleneck that restricts its application. In this paper, two-dimensional numerical simulations were performed to investigate the effectiveness of an upstream deflector on improving performance of the straight-bladed (H-type) marine current turbine. The effects of various key geometrical parameters of the deflector including position, length, and installation angle on the hydrodynamic characteristics of the VAMCT were then systematically analyzed in order to explore the mechanism underlying the interaction between the deflector and rotor of a VAMCT. As a result, the optimal combination of geometrical parameters of the deflector by which the maximum energy utilization efficiency was achieved was a 13.37% increment compared to that of the original VAMCT. The results of this work show the feasibility of the deflector as a potential choice for improving the energy harvesting performance of a VAMCT with simple structure and easy implementation.

Low Speed Vertical Axis Current Turbine (LS-VACT): Experimental Results

Depleting of fossil fuels and climate change problem as well as the pollutions arise make the renewable energy one of the best options for long-term usage. In hydropower energy extraction, vertical axis marine current turbine applications; Savonius turbine, which has the ability to operate in low speed current is suitable with the Malaysia’s sea conditions. However, due to the drawbacks which are low efficiency and low tip speed ratio, modifications need to be done to harness more power. Low Speed Vertical Axis Current Turbine is appeared to extract energy based on the Savonius rotor. In conjunction to this matter, laboratory work has been done in a way to study the relationship between Power Coefficient (Cp) and Tip Speed Ratio (λ), and also the relationship between Torque Coefficient (Ct) and Tip Speed Ratio (λ) at different current speed which are 0.32 m/s and 0.64 m/s.

Motion Response of a Novel Platform of Vertical Axis Marine Current Turbine

Some marine current harnessing technology require a platform as the base of the marine current turbine. Several potential locations of marine current energy are in deep water and in a strait with limited width, so a floating platform is required for the system. The design of a floating platform should consider the motion caused by the environmental load such as wave, current, wind. The platform should provide a smooth motion response during the operation. This paper compares the motion response of several platform concepts and proposes a novel platform that accommodates several vertical axis turbines. The method of analysis used in this paper is by comparing the response amplitude operates (RAO). The compared platforms are semi-sub platform, catamaran platform PLAT-1. The proposed 44.93 tones platform will accommodate eight vertical axis turbines with total capacity 23kW and installed in 100-200 m water depth. The maximum ocean current is 2.4 m/s significant wave height 25 years return period is 2.4 m wind speed 4.5 - 6 m/s. The results show that the new platform has better translational motions such as surge, heave, sway, but has varied results on rotational motions such as roll, pitch, and yaw.

Experimental demonstration of performance of a vertical axis marine current turbine in a river

An experimental station for marine current power has been installed in a river. The station comprises a vertical axis turbine with a direct-driven permanent magnet synchronous generator. In measurements of steady-state operation in varying flow conditions, performance comparable to that of turbines designed for significantly higher flow speeds is achieved, demonstrating the viability of electricity generation in low speed (below 1.5 m/s) marine currents.

Computational study of transient flow around Darrieus type cross flow water turbines

This study presents full transient numerical simulations of a cross-flow vertical-axis marine current turbine (straight-bladed Darrieus type) with particular emphasis on the analysis of hydrodynamic characteristics. Turbine design and performance are studied using a time-accurate Reynolds-averaged Navier–Stokes commercial solver. A physical transient rotor-stator model with a sliding mesh technique is used to capture changes in flow field at a particular time step. A shear stress transport k-ω turbulence model was initially employed to model turbulent features of the flow. Two dimensional simulations are used to parametrically study the influence of selected geometrical parameters of the airfoil (camber, thickness, and symmetry-asymmetry) on the performance prediction (torque and force coefficients) of the turbine. As a result, torque increases with blade thickness-to-chord ratio up to 15% and camber reduces the average load in the turbine shaft. Additionally, the influence of blockage ratio, profile trailing edge geometry, and selected turbulence models on the turbine performance prediction is investigated.

Effect of blade vortex interaction on performance of Darrieus-type cross flow marine current turbine

In this work, in-house computational fluid dynamics (CFD) code was utilized to simulate a cross-flow vertical-axis marine current turbine (straight-bladed Darrieus type). Particular emphasis was placed on the influence of interaction between vortices and blades on hydrodynamic performance. A physical transient-rotor–stator model with a sliding mesh technique was used to capture changes in flow field at a particular time step. The Spalart–Allmaras turbulence model was adopted for the turbulence. For a Darrieus-type marine current turbine, hydrodynamic characteristics such as power coefficient and flow behavior were then numerically investigated. The results suggest that vortices shed from previous blade passages and the close encounter of a rotor blade with these vortices can cause a variation in performance for this type of turbine during operation at different tip speed ratios.

Dynamic Performance Simulation of Hydraulic Transmission for Low Speed Vertical Axis Marine Current Turbine Using MATLAB Simulink

For Malaysia, ocean energy can be the best resource of green marine renewable energy. This is for the reason, the generation of the electricity by burning of fossil fuels produces undesired greenhouse gases and moreover the reserves of fossil fuels are being depleted and there is no accurate way to determine how much still remains. Turbines using hydraulic drive are being used for generating electricity by some manufacturers in the wind industry as an alternative to gearbox drive-trains because of reliability issues. Likewise, in the marine renewable sector, hydraulic-drive is an attractive option in terms of improved system efficiency, reliability and robustness. This paper presents a time domain simulation of hydraulic transmissions for Low Speed Vertical Axis Marine Current Turbines (VACT) using MATLAB Simulink software. These turbines are applied to harness marine current energy because of their relative simplicity and represent a promising technology to exploit low speed currents due to their small plants with reduced installation and maintenance costs.

Computational Fluid Dynamics Based Optimal Design of Vertical Axis Marine Current Turbines

Marine turbines are being increasingly used to harness kinetic energy of water and convert it into other useful forms of energy. Widespread commercial acceptability of these machines depends upon their efficiency. This largely depends upon the geometric features of the marine turbines such as number of blades, shape of blades etc. Researchers have been using experimental facilities to optimise these machines for maximum power generation. With the advent of advanced computational techniques, it has now become possible to numerically simulate the flow of water in the vicinity of marine turbines and monitor their performance output. In this work Computational Fluid Dynamics (CFD) based techniques have been used to analyse the effects of number of blades within the stator and rotor, of an in-house built Vertical Axis Marine Current Turbine (VAMCT), on the performance output of the turbine. Furthermore, an effort has been put forward towards better understanding of the flow structure in the vicinity of the blades during transient interaction between rotor and stator blades. This study provides vital information with regards to the flow sensors’ requirements and placements in order to monitor various blade configurations of a VAMCT in real world. The results of this study show that the torque output from a VAMCT is a strong function of blade configurations and there is a significant degradation in the performance output of marine turbines as the inequality between the number of rotor and stator blades increases. Hence, CFD has the potential to optimise the design of marine turbines and can be used as a potential modelling tool in the near future for on-line health monitoring of such systems.

Experimental Studies on Savonius-type Vertical Axis Turbine for Low Marine Current Velocity

Renewable energy resources need to be explored to maintain and meet energy demand and replace the slowly depleting fossil fuels. Malaysia, surrounded by sea with long coastlines, is poised to exploit the potential of this energy. This research work aims at designing a suitable device to extract energy from Malaysian sea current. Malaysia’s ocean has a low current velocity averaging 0.56 m/s, which is below the working velocity of presently available current energy devices. To overcome this velocity limitation, a Savonius-type Vertical Axis Marine Current Turbine (VAMCT) design was proposed. The experiment to measure the torque of a Savonius-type turbine, which hitherto has been used for wind energy application, is presented in this paper. The laboratory experiment was carried out in the towing tank facility in Marine Technology Laboratory at Universiti Teknologi Malaysia. The Savonius model was attached to the towing carriage and current flow was simulated by moving the carriage in still water. The results show that turbine with double stacking rotors each with two paddles and overlap ratio of 0.21 give the best performance.

Hydrodynamic analysis models for the design of Darrieus-type vertical-axis marine current turbines

This work reviews hydrodynamic analysis models developed for the design of Darrieus-type vertical axis marine current turbines, with particular emphasis on the prediction of hydrodynamic rotor performance, as well as their suitability for aiding the optimization process, either directly, or as a fast filter of potential blade profiles. In order to improve the performance of a marine current turbine it is necessary accurately to model the flow passing the turbine’s blades. Several types of models exist for Darrieus-type turbines, from momentum-based streamtube models to complex computational fluids dynamics (CFD) simulations. With continuously varying large angles of attack on the blades, the main issue is accurate prediction of the flow field around the rotor and thus its loads and torque. This is further complicated by the significant inherent unsteady hydrodynamic characteristics and potential for dynamic stall. Comparisons of the analytical results with experimental data are presented to compare these different models and thus illustrate their areas of suitability in this context. In conclusion, vertical axis machines have the potential of high power capture compared with that of their horizontal counterparts but this will depend on blade profile and design configuration, solidity, and tip speed ratio. None of the existing theoretical methods really captures the actual performance of the machines except for detailed CFD simulations, which are inevitably computational time intensive.

Numerical study of straight-bladed Darrieus-type tidal turbine

This paper presents developments in numerical simulations of a cross-flow vertical-axis marine current turbine (straight-bladed Darrieus type) with particular emphasis on rotor-performance prediction and hydrodynamic loads for structural design calculations. This study initially used theoretical double-multiple-streamtube models, followed by physical testing on a scaled-down model turbine and primarily numerical simulations. Numerical investigations of a proposed full-scale turbine (power coefficient, blade loads and flow behaviour) were undertaken using the developed computational models. The turbine design was studied using a time-accurate Reynolds-averaged Navier–Stokes (RANS) commercial solver. A transient-rotor-stator model with a moving mesh technique was used to capture the change in flow field at a particular time step. A shear stress-transport [Formula: see text] turbulence model was used to model turbulent features of the flow. The numerical results show good agreement with experimental measurements and the theoretical double-multiple-streamtube model. Turbine sensitivity to parametric variations was also demonstrated in the full-scale numerical study. This work concludes that the developed model can effectively predict hydrodynamic performance and structural design blade loads of a vertical-axis marine current turbine.

Development of a hydraulic control mechanism for cyclic pitch marine current turbines

Tidal power generation by means of marine current farms is potentially a large renewable energy resource which could be harnessed in many coastal waters. Its availability is highly predictable in time, and the technology promises high energy conversion efficiency along with a relatively low impact on sea life due to its relatively small disturbance of natural tidal flows. A series of devices have so far been proposed and developed for the extraction and conversion of kinetic energy present in tidal flows into useful electrical power [1]. Designs include horizontal axis turbines, vertical axis turbines, and devices with oscillating lift surfaces. Up to date no technology has firmly established itself. This paper describes a novel hydraulic control mechanism designed for vertical-axis marine current turbines of the straight-bladed Darrieus type. It has been found to significantly improve turbine efficiency over conventional Darrieus turbines when operated at low blade tip-speed to tidal-flow-velocity ratios (TSR) and to give the turbine the ability to self-start reliably. The control mechanism enforces a cyclic pivoting motion on the turbine blades as they move around their circular flight-path. The movement of the pitch control is of sinusoidal shape and is continuously variable in amplitude. The blade actuation is powered by the turbine's own rotation and is implemented using a swash-plate mechanism in conjunction with a hydraulic circuit for every blade. For surface piercing turbines, this control mechanism may be remotely positioned in a dry nacelle above sea level. If the appropriate design is applied, this can offer access to the cyclic pitch control mechanism, gearbox and generator, even when the turbine is operational, promising lower maintenance and operating costs compared with submerged systems.