Vertical Axis Tidal Current Turbine Research Articles

The study on the load and flow field of a twin-rotor vertical axis tidal current turbine

ABSTRACT The purpose of this paper is to investigate the influence of interference effects on the load and flow field of double-rotor vertical axis tidal current turbines. Numerical simulations were conducted using computational fluid dynamics (CFD) methods. The study demonstrates that interference effects result in significant changes in both the load and flow field of double-rotor turbines. Compared to single-rotor turbines, the power coefficient and force coefficient of double-rotor turbines increase by 21% and 28%, respectively. The stronger the interference effects, the more significant these differences become, as interference effects lead to an increase in flow velocity near the double-rotor turbines. As the tip speed ratio decreases and the spacing between the two rotors increases, interference effects gradually weaken, while rotor rotation direction also influences interference effects.

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.

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.

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.

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.

Investigations on the hydrodynamic interference of the multi-rotor vertical axis tidal current turbine

In the development of tidal energy, in order to extract more energy in the limited tidal farm, large-scale deployment of tidal current turbine is needed. In this paper, based on the PimpleDyMFoam solver in Open Source Fluid Dynamics Software (OpenFOAM), an effective numerical method is proposed for the two-dimensional VATCT (Vertical Axis Tidal Current Turbine). Secondly, the symmetrical simplified model is introduced to simulate the multi-rotor VATCT array. The interaction and wake characteristics of each turbine in different array layout schemes are studied in order to enhance the understanding of the interaction between multiple turbines. It is well known that the interaction between multiple turbines improves the overall power conversion efficiency, so it is of great significance to conduct in-depth research. The CFD numerical simulation results of the multi-rotor turbine array are compared in three aspects: blade force, wake flow field and power conversion efficiency. The results show that the power conversion efficiency of multi-rotor turbine array is higher than that of the stand-alone turbine. The smaller the spacing of each turbine in the multi-rotor turbine, the larger the overall output power. The single-row multi-rotor array in the form of opposite-rotation is more advantageous for energy acquisition. The analysis of the multi-rotor array from the aspect of the wake flow field can provide some insights into the reasons for the increased power conversion in the array. In this paper, force characteristics, wake characteristics and the energy efficiency of multi-rotor VATCT under different array layouts are considered comprehensively. The array optimization scheme proposed from the point of view of hydrodynamics will provide technical insights for the industrialization of large-scale VATCT array farm.

Numerical simulation of foil with leading-edge tubercle for vertical-axis tidal-current turbine

The main disadvantage of the vertical-axis turbine is its low coefficient of performance. The purpose of this work was to propose a method to improve this performance by investigating the hydrodynamic forces and the flow-field of a foil that was modified with a sinusoidal leading-edge tubercle. NACA 63(4)021 was chosen as the original foil since it has a symmetrical profile that is suitable for use on a vertical-axis tidal-current turbine. The study was conducted using a numerical simulation method with ANSYS-CFX Computational Fluid Dynamics (CFD) code to solve the incompressible Reynolds-Averaged Navier-Stokes (RANS) equations. Firstly, the simulation results of the original foil were validated with available experimental data. Secondly, the modified foils, with three configurations of tubercles, were modelled. From the simulation results, the tubercle foils, when compared with the original foil, had similar lift performances at low Angles of Attack (0-8 degrees of AoA), lower lift performances at medium AoA (8-19 degrees) and higher lift performances at high AoA (19-32 degrees). A tubercle foil with Height/Chord (H/C) of 0.05 can maintain the static stall condition until 32 degrees. Therefore, a vertical-axis turbine with tubercle-blades provides an opportunity to increase its performance by extending the operational range for extracting energy in the dynamic stall condition.

Forced Motion CFD Simulation and Load Refinement Evaluation of Floating Vertical-Axis Tidal Current Turbines

Abstract Simulation of the hydrodynamic performance of a floating current turbine in a combined wave and flow environment is important. In this paper, ANSYS-CFX software is used to analyse the hydrodynamic performance of a vertical-axis turbine with various influence factors such as tip speed ratio, pitching frequency and amplitude. Time-varying curves for thrust and lateral forces are fitted with the least squares method; the added mass and damping coefficients are refined to analyse the influence of the former factors. The simulation results demonstrate that, compared with non-pitching and rotating turbines under constant inflow, the time-varying load of rotating turbines with pitching exhibits an additional fluctuation. The pitching motion of the turbine has a positive effect on the power output. The fluctuation amplitudes of thrust and lateral force envelope curves have a positive correlation with the frequency and amplitude of the pitching motion and tip speed ratio, which is harmful to the turbine’s structural strength. The mean values of the forces are slightly affected by pitching frequencies and amplitudes, but positively proportional to the tip speed ratio of the turbine. Based upon the least squares method, the thrust and lateral force coefficients can be divided into three components, uniform load coefficient, added mass and damping coefficients, the middle one being significantly smaller than the other two. Damping force plays a more important role in the fluctuation of loads induced by pitching motion. These results can facilitate study of the motion response of floating vertical-axis tidal current turbine systems in waves.

Array Arrangement on Vertical Axis Tidal Current Turbine Using Free Vortex Model

Han, R.; Ma, Y., and Li, L., 2020. Array arrangement on vertical axis tidal current turbine using free vortex model. In: Yang, Y.; Mi, C.; Zhao, L., and Lam, S. (eds.), Global Topics and New Trends in Coastal Research: Port, Coastal and Ocean Engineering. Journal of Coastal Research, Special Issue No. 103, pp. 361–365. Coconut Creek (Florida), ISSN 0749-0208.In order to study the hydrodynamic performance of multiple vertical tidal current turbines, an analysis model based on free vortex model is proposed. By comparing with experiment data, the present model can obtain reasonable results. Then the hydrodynamic performance of twin-turbine and quad-turbine systems are studied using the present model. For twin-turbine system, five sets of turbines spacing and three sets of rotation direction are researched. And five sets of rotation direction are researched for quad-turbine system with one turbine spacing. By comparison, it is shown that positive effect on the relative power coefficient can be found at high TSR when turbines are side-by-side arrangement. At the same time, in most cases, it can obtain a higher relative power coefficient when turbines are rotating inward and have a smaller spacing. Due to the low computational time, the present method can be used in preliminary study on array arrangement of vertical axis tidal current turbine.

Numerical study on energy-converging efficiency of the ducts of vertical axis tidal current turbine in restricted water

Installation of the channeling device around a tidal turbine can stabilize flow field, increase flow velocity and improve energy utilization efficiency significantly. The application of channeling devices on improving the efficiency of vertical axis tidal turbines in restricted water has hardly been investigated. In the present study, two ducts with different inside wall shapes have been taken as examples to investigate the bank and free surface effects on energy-converging efficiency of the ducts around a vertical axis tidal current turbine in shallow and narrow water. The three dimensional viscous flow field around the ducts is simulated by using CFD technology. RANS equations are employed as viscous-flow solvers and the realizable two-layer k-ε turbulence model is applied to predict the energy-converging efficiency of the ducts. Investigation of grid dependence is conducted and grid independent solution is obtained by analyzing the numerical results of several sets of computational grids. For the duct around the vertical axis tidal current turbine near or piercing the free-surface of the water in some cases, Volume of Fluid (VOF) method is employed to capture the free surface. Based on the numerical results, it is known that the average energy flux density in W02 model is much larger than that in W01 model, so it can be concluded that the inside wall shape of the ducts dominates the energy-converging efficiency of the ducts in great extent and bank effect on energy-converging efficiency of the duct varies with inside wall shapes of the duct. What's more, the free surface plays an important role in the energy-converging efficiency of the ducts, and smaller clearance between free surface and the top of duct will induce higher energy-converging efficiency.

Numerical Study on the Vertical-Axis Tidal Current Turbine with Coupled Motions (Part I)

ABSTRACT Xu, G.; Li, H., and Wang, S., 2019. Numerical study on the vertical-axis tidal current turbine with coupled motions (Part I). In: Hoang, A.T. and Aqeel Ashraf, M. (eds.), Research, Monitor...

Analysis of Hydrodynamic Characteristics of Ocean Ship Two-unit Vertical Axis Tidal Current Turbines with Different Arrangements

Ji, R.; Sun, K.; Wang, S.; Li, Y., and Zhang, L., 2018. Analysis of hydrodynamic characteristics of ocean ship two-unit vertical axis tidal current turbines with different arrangements. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and OceanEngineering. Journal of Coastal Research, Special Issue No. 83, pp. 98–108. Coconut Creek (Florida), ISSN0749-0208.In order to study the hydrodynamic performance of the two-unit turbinesin different arrangements, a reasonable turbine layout plan was proposed to improve the power generation efficiency of tidal power stations. In this paper, the transient numerical simulation of a three-blade vertical-axis tidal current turbine is carried out, and the hydrodynamic performance of the turbine units with different arrangement (tandem, parallel, and staggered) is analyzed, and the influence of the mutual interference between the turbine units on the efficiency of the power generation is explored. Taking into account the same characteristics of the profile of the vertical axistidal current turbine blades along the extension, the model is simplified to two-dimensional. Firstly, based on the open source software OpenFOAM, a k-ω SST turbulence model and a PIMPLE algorithm are used for a 2D vertical axis tidal current turbine. A numerical simulation method is proposed and compared with the experimental results to verify the correctness of the numerical simulation method. Then the operation of a single turbine was simulated, and the variation of energy utilization with the tip speed ratio and the force characteristics of the turbine during operation were obtained. Finally, the vertical axis tidal turbine units with different arrangements are analyzed in detail, and the energy efficiency, force characteristics, and wake field of the vertical axis turbine units are compared and analyzed. For tandem tidal turbine units, the flow distance Dx of the two-unit turbines is used as a variable to study the effect of tidal turbine spacing on the hydrodynamic performance of downstream turbines. For parallel tidal turbines, the influence of the horizontal distance Dy and three different rotations on the hydrodynamic performance of tidal turbines is studied. For staggered turbine units, the relative distance Dr and the relative position angle ψ of the turbine are used as variables to study the relationship between the capacity of the turbine and the two parameters.

Numerical simulation on hydrodynamic performance of parallel twin vertical axis tidal current turbines

Single and parallel twin vertical axis hydro turbines were numerically simulated by using OpenFOAM software, studying the interference effects, such as torque and load of turbine, as well as hydrodynamic performance influenced by the distance and rotation forms between twin turbines, and analyzing the wake flow field to show the velocity profile distribution. The results showed that the average power of parallel twin turbines is always higher than the power of a single turbine, and the closer the lateral distance between turbines, the higher the power. When lateral distance approximates to 1.25 times turbine diameter, and turbines rotate in the opposite inward direction, the average energy efficiency value of parallel twin turbines is about 25 % higher than that of a single one. Additionally, opposite inward rotation is the best arrangement form for twin turbines to obtain more power and counteract lateral force.

Hydrodynamic performance of a vertical axis tidal current turbine with angular speed fluctuation

ABSTRACTThe angular speed of Vertical axis tidal current turbines (VATTs) should undulate in one periodic rotation given their inherent special structure. A coupled dynamic numerical simulation method is presented to study the effect of angular speed fluctuation on the performance of a VATT. The CFX User Fortran interface is applied to simultaneously solve the fluid conservation and rigid motion equations. The angular speed and acceleration of the turbine at specific time steps are determined by solving the moment equation of the rigid blade, and the force on the blade is obtained from the dynamic integral of the fluid field. The numerical simulation and experimental results suggest that coupled numerical simulation is necessary for small moment of inertia because the amplitude of the angular speed fluctuation is approximately 28% of the average value. Undulation of the load and the moment caused by unsteady angular speeds will reduce the turbine’s energy extraction.

Numerical Investigation of Contra Rotating Vertical-Axis Tidal-Current Turbine

In this study, the performance of a contra rotating vertical-axis tidal-current turbine was investigated. The incompressible unsteady Reynolds-averaged Navier-Stokes (U-RANS) equations were solved via two-dimensional (2D) numerical simulation using ANSYS Fluent computational fluid dynamics (CFD) code. An algorithm known as SIMPLE from the CFD code was used to calculate the pressure-velocity coupling and second-order finite-volume discretization for all the transport equations. The base turbine model was validated using the available experimental data. Three given scenarios for the contra rotating turbine were modeled. The contra rotating turbine performs better in a low tip speed ratio (TSR) than in a high TSR operation. In a high TSR operation, the contra rotating turbine inefficiently operates, surviving to rotate in the chaotic flow distribution. Thus, it is recommended to use contra rotating turbine as a part of new design to increase the performance of a vertical-axis tidal-current turbine with a lower TSR.

The influence of time step setting on the CFD simulation result of vertical axis tidal current turbine

The influence of time step setting on the CFD simulation result of vertical axis tidal current turbine

Hydrodynamic analysis of vertical-axis tidal current turbine with surging and yawing coupled motions

The hydrodynamic performance of the rotated vertical-axis tidal current turbine with another two (i.e. surge and yaw in this paper) degrees of freedom (DOF) coupled motion in unbounded uniform flow is analysed by the dynamic mesh. The effects of the turbine's hydrodynamic loads have been studied and illustrated considering the 3-DOF coupled motion. Numerical results show that: 1) the effects of the hydrodynamic load is mainly caused by the surging motion, but the effects of the yawing motion is reflected when its frequency is greater than that of the surging; 2) There are fluctuations in the envelope curves of the thrust and lateral force, rotational and yawing moment coefficients of the turbine, and the fluctuation amplitudes have a positive correlation with the surging and yawing motion frequencies; 3) the calculation formula of the turbine's hydrodynamic loads coefficients are obtained. The results of the hydrodynamic loads calculated by the formulations and CFD numerical simulation show good agreements, which verify the calculation formulas reasonably. The results of this research can provide relevant data for the hydrodynamic analysis of turbines with multi-degree of freedom motion and the structural design.

Optimization on the Law of Variable-Pitch Vertical-Axis Tidal Current Turbine

In order to improve the hydrodynamic performance of the vertical-axis variable-pitch current turbine, with analyzing on the existing design mentality of blade control mechanism, an optimized law of variable-pitch vertical-axis tidal current turbine was given in terms of the instantaneous moment coefficient of the blade. A method for solving the lift - drag coefficient of Blade by wind - hole test data is given. The optimized kinematic model has a significant reference value for the further development of vertical axis turbine model test.

Structural Dynamic Analysis of a Tidal Current Turbine Using Geometrically Exact Beam Theory

This paper presents a numerical study of the dynamic performance of a vertical axis tidal current turbine. First, we introduce the geometrically exact beam theory along with its numerical implementation the geometric exact beam theory (GEBT), which are used for structural modeling. We also briefly review the variational-asymptotic beam sectional analysis (VABS) theory and discrete vortex method with free-wake structure (DVM-UBC), which provide the one-dimensional (1D) constitutive model for the beam structures and the hydrodynamic forces, respectively. Then, we validate the current model with results obtained by ANSYS using three-dimensional (3D) solid elements and good agreements are observed. We investigate the dynamic performance of the tidal current turbine including modal behavior and transient dynamic performance under hydrodynamic loads. Finally, based on the results in the global dynamic analysis, we study the local stress distributions at the joint between blade and arm by VABS. It is concluded that the proposed analysis method is accurate and efficient for tidal current turbine and has a potential for future applications to those made of composite materials.

Application of 2D numerical model to unsteady performance evaluation of vertical-axis tidal current turbine

Tidal current energy is renewable and sustainable, which is a promising alternative energy resource for the future electricity supply. The straight-bladed vertical-axis turbine is regarded as a useful tool to capture the tidal current energy especially under low-speed conditions. A 2D unsteady numerical model based on Ansys-Fluent 12.0 is established to conduct the numerical simulation, which is validated by the corresponding experimental data. For the unsteady calculations, the SST model, 2×105 and 0.01 s are selected as the proper turbulence model, mesh number, and time step, respectively. Detailed contours of the velocity distributions around the rotor blade foils have been provided for a flow field analysis. The tip speed ratio (TSR) determines the azimuth angle of the appearance of the torque peak, which occurs once for a blade in a single revolution. It is also found that simply increasing the incident flow velocity could not improve the turbine performance accordingly. The peaks of the averaged power and torque coefficients appear at TSRs of 2.1 and 1.8, respectively. Furthermore, several shapes of the duct augmentation are proposed to improve the turbine performance by contracting the flow path gradually from the open mouth of the duct to the rotor. The duct augmentation can significantly enhance the power and torque output. Furthermore, the elliptic shape enables the best performance of the turbine. The numerical results prove the capability of the present 2D model for the unsteady hydrodynamics and an operating performance analysis of the vertical tidal stream turbine.