Vertical-axis Turbine Research Articles

Structural dynamic characteristics of vertical axis wind and tidal current turbines

Vertical axis turbines have received great attention in both offshore wind and tidal current energy communities considering their advantages of economic design and unidirectional operation. However, their commercialization process is rather slow compared with the development of horizontal axis turbines due to technical challenges resulting from higher loads from unsteady aero/hydrodynamic forces, centrifugal forces and gravity of the structures. These are mainly because, while the inherent unsteady tangential pulls and fatigue loads intensify the structural vibration, aggravating structural safety and fatigue life, the relationship between the geometric parameters and the structural responses of blades remains unclear. Therefore, in order to clarify this issue, in this study, we focus on the modal and transient analysis of vertical axis turbines using multi-body dynamics, geometrically exact beam theory and detached eddy simulation. We find that the natural frequency of the rotor is directly related to the ratio of blade length and arm length. The effect of arms cannot be ignored in the structural analysis of the turbine. Moreover, an increase of blade length intensifies the deformation and vibration of the turbine’s structure, making the turbine more prone to fatigue failure. This article is expected to extend the existing knowledge of wind and tidal current turbines and provide a reference for choosing proper design parameters and developing suitable-capacity vertical axis turbines.

Investigation of Vertical-axis Tidal Turbine Mechanical Strength using FSI Analysis based on Blade Profile

Abstract Tidal energy, as a renewable energy source harnessed from the ocean, holds substantial promise owing to its heightened energy density, reliability, and longevity. An investigation encompassing the deployment of tidal stream electricity from 2003 through August 2020 revealed that blade malfunction was identified as the primary reason for system failures, with generator and monitoring system failures occurring subsequently. The majority of the research that has been done on the design of vertical-axis tidal turbine blades has focused on how well the blade performs in terms of power output without taking into account the generation of mechanical force. This force can potentially shorten the blade’s lifetime when implemented in a real-world scenario. By modelling a steady-state fluid-structure interaction (FSI) configuration, this study examines how the shape of the turbine blades affects the amount of mechanical force they generate, particularly in vertical-axis tidal turbines. The type of blade profile is the variable under consideration, and the stress levels experienced by a structure are influenced by the type of blade profile used. When comparing symmetrical and asymmetrical NACA straight blade types under similar climatic conditions, it has been found that the blade profile plays a significant role. Asymmetrical blade profiles, in particular, generate a higher lift force compared to symmetrical ones, thereby affecting stress levels more noticeably.

Publisher's Note: “Numerical analysis of the impact of helical-blade design on flow characteristics and energy utilization in vertical-axis water turbine [Phys. Fluids 36, 085182 (2024)

Publisher's Note: “Numerical analysis of the impact of helical-blade design on flow characteristics and energy utilization in vertical-axis water turbine [Phys. Fluids <b>36</b>, 085182 (2024)

Design and Optimization of a Gorlov-Type Hydrokinetic Turbine Array for Energy Generation Using Response Surface Methodology

Hydrokinetic arrays, or farms, offer a promising solution to the global energy crisis by enabling cost-effective and environmentally friendly energy generation in locations with water flows. This paper presents research focused on the design and optimization of a Gorlov-type vertical-axis hydrokinetic turbine array for power generation. The study involved (i) numerical simulations using computational fluid dynamics (CFD) software with the six degrees of freedom (6DoF) tool, (ii) optimization techniques such as response surface methodology, and (iii) experimental testing in natural environments. The objective was to develop an efficient system with low manufacturing and maintenance costs. A key finding was that the separation distance between rotors, both along and across the fluid flow, is a critical parameter in designing hydrokinetic arrays. For this study, a triangular array configuration, termed Triframe, was used, consisting of three Gorlov-type turbines with four blades each. The optimization process led to separation distances based on the diameter (D) of the turbines, with 15.9672D along the fluid flow (X) and 4.15719D across the flow (Y). Finally, an experimental scale model of the hydrokinetic array was successfully constructed and characterized, demonstrating the effectiveness of the optimization process described in this study.

A volume‐of‐solid implicit volume penalty method for moving‐body flows

AbstractAn original Immersed Boundary Method for solving moving body flows is proposed. This method couples (i) a Lagrangian Volume‐of‐Solid description of the solid object avoiding conservation issues and (ii) a robust implicit volume penalty forcing embedded in a low‐Mach number projection method to account for the solid's impact on the fluid dynamics. A new composite velocity field is introduced to describe both solid and fluid domains in a single set of governing equations. The accuracy of the method has been assessed on several academic cases, involving stationary or moving bodies and with different mesh resolutions. The predicted forces on the solid are in excellent agreement with body‐fitted reference cases. The system of equations is also proven to be fully mass conservative. Application of the method on a two‐dimensional vertical axis turbine case shows a reduction in computational cost compared to a body‐fitted method.

Semi-Empirical Model Based on the Influence of Turbulence Intensity on the Wake of Vertical Axis Turbines

In the context of energy shortages and the development of new energy sources, tidal current energy has emerged as a promising alternative. It is typically harnessed by deploying arrays of multiple water turbines offshore. Vertical axis water turbines (VAWTs), as key units in these arrays, have wake effects that influence array spacing and energy efficiency. However, existing studies on wake velocity distribution models for VAWTs are limited in number, accuracy, and consideration of influencing factors. A precise theoretical model (Lam’s formula) for wake lateral velocity can better predict wake decay, aiding in the optimization of tidal current energy array designs. Turbulence in the ocean, serving as a medium for energy exchange between high-energy and low-energy water flows, significantly impacts the wake recovery of water turbines. To simplify the problem, this study uses software ANSYS Fluent 2020 R2 for two-dimensional simulations of VAWT wake decay under different turbulence intensities, confirming the critical role of turbulence intensity in wake velocity decay. Based on the obtained data, a new mathematical approach was employed to incorporate turbulence intensity into Lam’s wake formula for VAWTs, improving its predictive accuracy with a minimum error of 1%, and refining some parameter calculations. The results show that this model effectively reflects the impact of turbulence on VAWT wake recovery and can be used to predict wake decay under various turbulence conditions, providing a theoretical basis for VAWT design, optimization, and array layout.

The Influence of Structural Parameters on the Ultimate Strength Capacity of a Designed Vertical Axis Turbine Blade for Ocean Current Power Generators

An ocean current power generator is a power plant that uses kinetic energy from ocean currents to generate electricity. Considering that the blade is the component that receives the biggest load from seawater currents, its structural design should be strong enough to sustain the applied load. Therefore, this research seeks a suitable design and material for turbine blades using the finite element method (FEM). A NACA 0021 blade with a total length of 3600 mm is used for the base geometry. A parametric study was conducted by varying the spacing between the supports, the pitch angle, the material, and the frame model. Considering a high load, the suitable amount of space between the stiffeners was 2200 mm. It was found that a pitch angle variation between −20° and +20° did not significantly affect the strength of the blade structure. The frame geometry variation caused the rigidity and cross-section area of the blade to differ. Therefore, web-shaped or bar-shaped frames are preferable because they have optimal maximum load-to-weight ratios. The material variation analysis resulted in CFRP material being chosen because it had a high maximum load/weight ratio and a high maximum stress.

Design and Analysis of a Vertical Axis Ocean Current Turbine Tunnel Using SolidWorks Computational Fluid Dynamics

The development of renewable energy in the marine power generation sector presents a promising approach to producing electrical energy in a sustainable and environmentally friendly manner. Indonesia, with its vast oceanic territory, holds significant potential for harnessing marine energy. However, the relatively slow speed of ocean currents in the region, typically ranging from 0.1 m/s to 1.5 m/s, poses a challenge to the efficiency of marine power generation. To overcome this limitation, this research focuses on the design and analysis of a vertical-axis ocean current turbine tunnel aimed at increasing the speed of ocean currents, thereby enhancing the overall efficiency of energy production. The study combines a thorough literature review with experimental research methods, utilizing SolidWorks Computational Fluid Dynamics (CFD) software to simulate the tunnel's impact on ocean current velocity. The simulations reveal that the tunnel construction significantly boosts current speeds, increasing them from 1.0 m/s to 1.7 m/s, and from 1.5 m/s to 2.6 m/s. This increase in velocity directly translates to higher kinetic energy available for conversion into electrical power by the turbine. Moreover, the study shows that the tunnel construction contributes to a more uniform flow of ocean currents, as evidenced by the Reynolds numbers obtained—100.250 at a current speed of 1.0 m/s and 150.375 at 1.5 m/s. These values, being below 2000, indicate laminar flow conditions within the tunnel, which are beneficial for optimizing turbine performance by reducing turbulence and ensuring a stable energy output. The findings underscore the effectiveness of the tunnel design in improving the efficiency of vertical-axis ocean current turbines, making it a viable solution for enhancing renewable energy production in regions with low ocean current speeds.

Energy Conversion by Helical Hydrokinetic Turbine in A Pipe

Hydrokinetic turbines are mechanisms designed for the purpose of utilizing the kinetic energy present in the movement of water bodies like rivers, tidal currents, or ocean currents, and transforming it into electrical power. These turbines function based on a principle akin to that of wind turbines; however, they are positioned underwater to harness the energy of the water flow. This study focuses on the fundamentals of hydrokinetic turbines and presents existing research. Additionally, simulations have been conducted to observe how the hydrokinetic turbine responds hydrodynamically inside a pipe. A three-bladed vertical-axis helical hydrokinetic turbine was installed within a circular conduit and subjected to analysis under varying flow conditions. The k-ω SST turbulence model was employed in the analyses. The results indicated that increasing the turbine's angular velocity initially raises the torque and the power coefficient until a peak is reached, after which the power coefficient decreases. The highest power coefficient was observed at a flow velocity of 2 m/s. Additionally, consistent with previous studies, the hydrokinetic turbine within the pipe surpassed the Betz limit.

Numerical analysis of the impact of helical-blade design on flow characteristics and energy utilization in vertical-axis water turbine

In this study, a vertical-axis helical-blade water turbine is innovatively proposed by drawing on the design scheme of the traditional straight-blade turbine, compared to which this blade form can effectively improve the self-starting capability and energy capture efficiency of the turbine. The study analyzes the hydrodynamic performance of the device under different parameters using CFD (computational fluid dynamics) software STAR-CCM+ and overlapping mesh technique, and the CFD simulation results are verified with published experimental work. First, the design concept of the hydraulic turbine is presented, focusing on the design of the blades and transmission mechanism to ensure the stability of the structure. Second, the effect of two-dimensional parameters on the flow field characteristics and efficiency is investigated, and then three-dimensional design parameters, such as blade helix angle and hub-to-tip ratio, are considered. The results show that a 20% increase in blade density results in a 10.74% increase in efficiency. Regarding flow velocity, a maximum output of 2.4 kW was achieved for four operating conditions (1.0, 1.5, 2.0, and 2.5 m/s). In addition, the average dynamic torque of the helical-blade turbine was 16.44% higher than that of the straight-blade turbine, indicating superior self-starting capability. It was also found that at an aspect ratio of 1.5–1.75 and a helix angle of 80°, the energy capture efficiency of the helical-blade turbine was 33.7%, which was 45.3% higher than that of the straight-blade turbine. Comparative analysis shows that the vertical-axis helical-blade turbine has favorable hydrodynamic performance, especially under low flow conditions, and the design scheme shows obvious advantages, which makes up for the defects of the traditional vertical-axis straight-blade turbine with poor self-starting ability and low efficiency, and fills up the research gaps of vertical-axis turbine design optimization, which is of certain research value.

Vertical axis turbine simulations based on sliding and overset meshes

Vertical axis turbine simulations based on sliding and overset meshes

Hydrodynamic performance analysis of dual vertical axis turbine

Abstract This article adopts a biomimetic approach and uses the profile of the fastest sailfish in the ocean as the airfoil profile of a water turbine. Integrating centrifugal and axial flow turbines on one drive shaft can effectively integrate wave and current energy (wave current integration). The wake of a centrifugal turbine flows into the flow field of an axial flow turbine, and based on the Kantar effect, the energy harvesting coefficient of the axial flow turbine is improved. The five blades of the axial flow turbine and centrifugal turbine are subjected to uneven forces, resulting in torsional and radial forces on the drive shaft, causing periodic series motion of the turbine and reducing the overall lifespan of the machine.

A methodology for modelling the vertical-axis turbine in two-dimensional (2D) based on the theory of actuator cylinder model

A methodology for modelling the vertical-axis turbine in two-dimensional (2D) based on the theory of actuator cylinder model

Performance Improvement of a Straight-Bladed Darrieus Hydrokinetic Turbine through Enhanced Winglet Designs

The global climate and energy crisis have underscored the importance of sustainability in energy systems and their efficiency. In the case of vertical axis turbines (VATs) for hydrokinetic applications, the increment in efficiency is a topic of interest. Using winglets as passive flow control devices has the potential to improve the power coefficient of straight-bladed (SB) Darrieus turbines highly due to their impact in the dynamics of the flow close to the tip blade and the general impact in the hydrodynamic performance of each blade. The aim of the present work is to study the influence of the geometric parameters of a symmetric winglet in the performance of an SB-VAT for hydrokinetic applications via numerical simulations based on Computational Fluid Dynamics (CFD). Several simulations were performed in Star CCM+ v2206 varying the cant and sweep angles of the designed winglet. Numerical results show that a cant angle of 45° in combination with a sweep angle of 60° achieved the highest power coefficient with an increment around 20% with respect to the model without winglets. Furthermore, the vortical flow structures that form around straight and winglet blades are examined. This involves assessing the distribution of pressure and skin friction coefficients at different blade azimuthal positions during a turbine revolution. In general, the predicted increment in performance is related to the influence of the winglets in the strength of the tip vortices and in the delay in the flow separation.

Systematic Review of Computational Fluid Dynamics Modelling and Simulation Techniques Employed in Vertical Axis Hydrokinetic Turbines

At present, Computational Fluid Dynamics (CFD) is being utilized to explore tidal and hydrokinetic turbine systems, advancing comprehension of turbulent flow phenomena and raising the accuracy of performance predictions for these fluid-driven turbines. Consequently, this utilization of CFD contributes to the optimization of efficiency in these devices. Turbines are subject to variations from the best design point due to the influence of fluctuating flow rates, despite the findings of recent research that have identified the ideal design points. In contrast to conventional literature reviews, systematic analysis offers numerous advantages. The methodological strategy applied in this study entailed cross-referencing the findings obtained from Web of Science (WOS) and Scopus databases to establish the comprehensiveness as well as reliability of researcher data. Improving the review process, elevating the prominence of the field of study, and establishing critical priorities to mitigate research bias are all potential strategies for enhancing the quality of these evaluations. This research divides its findings into three core themes: (1) Performance assessment for practical implications, (2) Numerical analysis for theoretical insights, and (3) Design parameter optimization for engineering relevance. These themes collectively provide a well-rounded examination of the research outcomes across practical, theoretical, and engineering dimensions. Finally, the research findings have the potential to act as a significant point of reference for informing the best design considerations pertaining to vertical axis turbines.

Numerical Study on Hydrodynamic Performance of a Pitching Hydrofoil with Chordwise and Spanwise Deformation

The hydrofoil plays a crucial role in tidal current energy (TCE) devices, such as horizontal-axis turbines (HATs), vertical-axis turbines (VATs), and oscillating hydrofoils. This study delves into the numerical investigation of passive chordwise and spanwise deformations and the hydrodynamic performance of a deformable hydrofoil. Three-dimensional (3D) coupled fluid–structure interaction (FSI) simulations were conducted using the ANSYS Workbench platform, integrating computational fluid dynamics (CFD) and finite element analysis (FEA). The simulation involved a deformable hydrofoil undergoing pitching motion with varying elastic moduli. The study scrutinizes the impact of elastic modulus on hydrofoil deformation, pressure distribution, flow structure, and hydrodynamic performance. Coefficients of lift, drag, torque, as well as their hysteresis areas and intensities, were defined to assess the hydrodynamic performance. The analysis of the correlation between pressure distribution and deformation elucidates the FSI mechanism. Additionally, the study investigated the 3D effects based on the flow structure around the hydrofoil. Discrepancies in pressure distribution along the spanwise direction result from these 3D effects. Consequently, different chordwise deformations of cross-sections along the spanwise direction were observed, contributing to spanwise deformation. The pressure difference between upper and lower surfaces diminished with increasing deformation. Peak values and fluctuations of lift, drag, and torque decreased. This study provides insights for selecting an appropriate elastic modulus for hydrofoils used in TCE devices.

Vertical-Axis Tidal Turbines: Model Development and Farm Layout Design

In this paper, we propose a new 3D model for vertical-axis tidal turbines (VATTs) embedded in the shallow-water code SHYFEM. The turbine model is based on the Blade-Element∖Momentum (BEM) theory and, therefore, is able to predict turbine performance based on the local flow conditions and the geometric characteristics of the turbine. It is particularly suitable for studying turbine arrays, as it can capture the interactions between the turbines. For this reason, the model is used to test a tidal farm of 21 devices with fluid dynamic simulations. In particular, we deploy the farm at Portland Bill, which is a marine site characterised by a wide spread in the direction of the tidal currents during a flood-ebb tide cycle. We optimised the lateral and longitudinal spacing of the turbines in a fence using computational fluid dynamics simulations and then performed a sensitivity analysis by changing the distance between the fences. The results show that the greater the distance between the fences, the higher the power output. The increase in power generation is around 16%, but this implies a huge increase in the horizontal extent of the farm. Further assessments should be carried out, as the expansion of a marine area dedicated to energy exploitation may conflict with other stakeholder interests.

Bioinspired Fluid Dynamic Designs of Vertical-Axis Turbines: State-of-the-Art Review and the Way Forward

Abstract With the increasing popularity of vertical axis turbines (VATs), researchers are now focusing on their performance improvement. Instead of adopting conventional means of performance improvements such as augmentation techniques and exhaustive parametric design optimization, the bio-inspired turbine designs have become a center of attraction, especially during the last decade. This review article attempts to compile the bio-inspired designs belonging to the VATs. Bio-inspired designs implemented in Savonius, Darrieus, Nautilus, and Seed-inspired turbines are elaborated besides giving a detailed explanation of the corresponding bio-organism and natural phenomenon. How the working principles of bio-organisms emulated in the form of fluid dynamic design are explained thoroughly in this paper. The bio-inspired designs for VATs are then classified pragmatically for the future designs. Research gaps are highlighted for the aspiring researchers, and this is followed by the important strategies and allied challenges.

Two-stage Taguchi-based optimization on dynamically-vented blade flaps to enhance the rotor performance of a Savonius turbine

Among the vertical-axis turbine groups for small-scale wind and hydrokinetic applications, the Savonius type is considered practical due to its simple construction, easy maintenance, and good self-starting characteristics. Unfortunately, it has a poor efficiency due to the exertion of negative torques during its returning sweeps. Recently, the technique of controlled dynamic venting has been shown to reduce this negative torque on a two-bladed Savonius rotor while preserving its omnidirectional capability. That investigation was extended in this numerical study by refining the controllable flaps of the same rotor to improve its performance using a two-stage optimization procedure. In the first stage, the design parameters of the controllable flaps were optimized using the Taguchi and Analysis of Variance (ANOVA) methods. In this analysis, the flap length was found to be the most significant parameter affecting the rotor performance with a contribution ratio of 79.8%, in contrast to a ratio of only 6.7% by the least effective parameter: the flap opening angle. The first optimization stage produced an improvement of 16.7% on the average power coefficient (CP) of the vented rotor, compared to the unvented one, at the optimal tip-speed ratio (TSR) of 1.0. In the second stage, the flap length was refined further to a shorter flap of 22.5% of the blade length, resulting in an improvement of 21% on the same metric at the same TSR. Crucially, these controllable flaps only used an energy cost of 6.1% of the total energy produced by the rotor, a significant improvement from the 12.2% energy cost obtained in the previous study.

Experimental investigation of motion response and mooring load of semi-submersible tidal stream energy turbine under wave-current interactions

Tidal stream energy turbines, mounted on floating platforms, harness higher current velocities at the water's surface across broader marine areas, which reduces construction costs. However, the interaction between waves and currents critically influences these platforms' motion patterns. This dynamic becomes more complex with a rotating turbine, challenging power efficiency, and increasing fatigue load. This study presents physical modeling and analysis of a semi-submersible platform equipped with a vertical-axis turbine. The proposed design features a Tri-floater semi-submersible, a suspended chain mooring system, and a Vertical-Axis Tidal Turbine. This study assesses the system's behavior under varying marine conditions, including pure wave, pure current, and combined wave-current scenarios. This study focuses on investigating the effects of structural coupling wave approach angles and evaluating the system's multi-degree-of-freedom motion response and mooring loads. Findings reveal that wave-current interactions significantly affect the motion and mooring tension of a floating tidal stream energy turbine. Wave periods mainly control motion periodicity; wave height influences its extent, and current velocity sets the equilibrium motion state and angle. Additionally, the rotation of the rotor introduces a secondary effect that significantly increases mooring tension. The study also elucidates the pronounced interdependence between the platform's motion and mooring loads.