Vertical Axis Hydrokinetic Turbine Research Articles

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.

Exploring the impact of flexible membranes on the performance of H- and S-type hydrokinetic turbines: An experimental investigation

Vertical axis hydrokinetic turbines (VAHTs) have the potential to harness deep-sea current energy without the need for a yaw mechanism. However, H-VAHTs have weak self-starting capabilities, and S-VAHTs also face startup dead point issues. To address the self-starting challenges of VAHTs, this study proposes attaching flexible membranes to the blades of VAHTs. The impact of flexible membranes on the performance of both types of VAHTs is evaluated through Particle Image Velocimetry (PIV) water flume experiments. The results demonstrate that attaching flexible membranes to the blade surfaces resolves the self-starting dead point issue for both turbines, with a greater improvement in self-starting performance for H-VAHTs than for S-VAHTs. The study found that for both turbines, attaching flexible membranes with a large opening on the blade’s outer side offers the best self-starting performance and power output. However, the flexible membranes reduced the CP of H-VAHTs, while slightly enhancing the performance of S-VAHTs. PIV tests showed that the flexible membranes form a cup-shaped structure when facing the flow. The pressure difference between the inside and outside of the membranes generates additional static torque, improving the self-starting performance of both turbines. Furthermore, even with one or two membrane blades missing, the self-starting capability of H-VAHTs was still enhanced; flexible membranes with a certain installation angle can also be attached to the endplates of S-VAHTs to address startup dead issues. In summary, attaching flexible membranes to VAHTs improves their self-starting performance and ensures power output, thereby facilitating the application of such turbines in deep-sea areas with low flow velocities.

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.

Enhancing savonius rotor model with additional grooves on hydrokinetic turbine performance

Hydrokinetic turbines use different rotors for technological and economic reasons. Even though it performs poorly, vertical-axis hydrokinetic turbines use the Savonius rotor. The object of research is a Savonius rotor model with additional grooves. The study addresses the need to improve the efficiency and overall performance of Savonius rotor models in hydrokinetic turbines, which are widely used for harnessing energy from flowing water currents. The problem involves understanding how different groove configurations affect the aerodynamic behavior and energy extraction efficiency of the Savonius rotor in hydrokinetic turbine applications. The test results revealed that incorporating grooves led to notable improvements in efficiency (ɳ) and coefficient of drag (CD). Grooved blades exhibited a maximum efficiency of 30.97 % and a maximum drag coefficient of 2.71. Notably, blades with a groove width of 12.5 mm emerged as the optimal model, demonstrating an efficiency peak of 35.66 % and a drag coefficient 3.08. This indicates a substantial increase in efficiency by 4.69 % and a corresponding rise in the drag coefficient by 0.37 for grooved blades. The grooves on grooved blades increase friction, improving performance. Grooved rotor blades improve turbine performance significantly. Savonius rotor models in hydrokinetic turbines extract more energy by optimizing groove width and arrangement to maximize drag coefficient and efficiency. This research affects hydrokinetic turbine design and optimization for renewable energy generation. Engineers and designers can improve the performance and efficiency of the Savonius rotor model in hydrokinetic turbine applications by applying this study’s findings

Numerical modeling and CFD simulation of diffuser augmented dual vertical axis hydrokinetic Banki-Michell turbine

Hydrokinetic Banki turbines present an affordable, technically feasible, environmentally friendly technology. Their construction without requiring more expensive structures like diversion weirs, canals, forebay, and penstock, makes their initial investment much lower than commonly used horizontal Banki turbine of the same capacity. The possibility to install in the existing canals for Ultra Low Head applications is the additional motivating factor for this research. The system studied includes two Banki runners without internal shafts mounted vertically side by side surrounded by nozzle and diffuser structures. In the first scenario, Nozzle and then the Nozzle-diffuser augmented structures were separately studied to enhance the output of the runner for ultra-low head application, and the effects of each on the speed, pressure, and power output were analyzed. For the case of commonly used Banki, without nozzle and diffuser augmentation the speed for Ultra Low Head was minimum and determined to be 344 rpm, which is far below the recommended value of 800 rpm for safe operation at a flow rate of 1 m^3/s. In view of this, in the present study the enhanced speed on account of improvement was found to be 850 rpm and 1025 rpm for the design without and with diffuser assemblies respectively. Besides, the performance is seen to be improved by 7.6% with the diffuser as compared with the one without diffuser assembly. Detailed simulation results are presented and discussed: 3D ANSYS-FLUENT optimization result provided optimum number of blades for each runner to be 19 and with the optimum throat width in both cases as 202 mm. On account of the lack of any results reported so far for this innovative geometry, validation of the simulated results was carried out with reported results for the dual horizontal axis Banki turbines with good agreement.

Numerical analysis of inflow turbulence intensity impact on the stress and fatigue life of vertical axis hydrokinetic turbine

The present study aims to analyze the effect of upstream turbulence intensity on the hydrodynamic and structural performance of the straight-blade vertical axis turbine. To achieve this, a one-way fluid structure interaction analysis is conducted within the ANSYS workbench environment. Initially, computational fluid dynamics (CFD) simulation is performed at different values of upstream velocity values. Additionally, the impact of upstream turbulence intensity is also analyzed. The CFD simulation results were validated against published experimental work. Once CFD simulation is performed then computed fluid loads are transferred to the ANSYS mechanical structural module. Finite element modeling is performed to compute the stresses and the fatigue life. The study reveals that increasing the upstream turbulence intensity from 5% to 20% leads to 8.6% improvement in the turbine's power performance. However, turbulence intensity also results in 35.6% increase in Von-Mises stresses produced within the designed turbine. However, even with this increase, the Von-Mises stresses remain below a critical threshold, measuring at 173.34 MPa when the upstream water velocity is 1.4 m/s, and the inflow turbulence intensity is at 20%. This stress level is well within the material's yield strength, ensuring the turbine's structural integrity. Moreover, the simulation results emphasize that turbulence intensity has a significant impact on the turbine's fatigue life. Further, it is predicted that an increase in turbulence intensity from 5% to 20% leads to a significant 40% reduction in the turbine's fatigue life. The stress analysis results reveal that struts, strut–blade joints, and strut–shaft joints are the key stress concentration areas. The results suggested that an increase in upstream turbulence intensity has favorable impact on turbine performance, however, for highly turbulent flows turbine should have higher strength and key areas should be focused on designing turbine for such flow conditions.

Enhancing the performance of vertical axis hydrokinetic Savonius turbines using a novel cambered hydrofoil profile for rotor blades

A novel rotor blade configuration using a cambered hydrofoil profile is developed to enhance the output power. Several design variables are considered including camber angle, overlap ratio, and camber position, in addition to integrating endplates. To assess the performance parameters at different design conditions, a comprehensive three-dimensional unsteady incompressible turbulent flow model based on Reynolds-Averaged Navier-Stokes equations combined with k-ω model is developed. The predicted numerical results is validated using the available numerical and experimental data. The findings indicate that using Savonius rotor with hydrofoil profile results in a substantial increase in the maximum output power for all investigated camber angles compared to the conventional semi-circular rotor. At a flow velocity of 0.4 m/s and an overlap ratio of 0.15, the Savonius rotor with hydrofoil profile attains a maximum power coefficient of 0.21 at a camber angle of 105°. By increasing the camber angle to 140°, the maximum power coefficient reaches 0.26 whereas it is 0.13 for the conventional design. The camber position at 50 % of the chord length achieves the highest power coefficient for all studied cases. In addition, adding the endplates significantly enhances the power coefficient. The current findings provide a promising approach in developing Savonius rotor blades configuration by utilizing hydrofoil profile.

Numerical comparison and efficiency analysis of three vertical axis turbine of H-Darrieus type

Hydropower is an important source of energy in Latin America. Many countries in the region, including Brazil, Peru, Colombia, and Chile, rely heavily on hydropower plants to meet their energy needs. However, there are also challenges related to the use of hydropower in the region, such as the construction of dams that can have negative impacts on ecosystems and local communities. A new alternative is the production of energy through hydrokinetic turbines because they are a clean and renewable energy source that does not emit greenhouse gases. In addition, its production is predictable and can be generated in a variety of environments, from coasts to rivers and canals. Within the hydrokinetic turbines are the H-Darrieus turbines although they are still under development, they are seen as an important opportunity to diversify the energy matrix and reduce dependence on fossil fuels. The main purpose of this study is to determine and compare the efficiency of three Darrieus H-type vertical axis hydrokinetic turbines numerically. The turbines were configured with different solidities. The NACA 0018 profile was used for the turbine design. The study was carried out using the ANSYS® Fluent 2022R2 software, two-dimensional (2D) simulations set up constant operating conditions. Rotation speed variations have been set between 21 and 74 RPM with 10 rpm increments. Furthermore, the General Richardson extrapolation method is used for the analysis of mesh convergence, monitoring the turbine power coefficient as a convergence parameter. The numerical results show that the turbine H-Darrieus with a solidity of 1.0, a wider operating range, and lower power and torque coefficient. At low TRS, the largest solidity provided the best efficiency and the greatest self-starting capability, but it also had the smallest operating range

Deep Learning-Based Prediction of Unsteady Reynolds-Averaged Navier-Stokes Solutions for Vertical-Axis Turbines

The following study investigates the effectiveness of a deep learning-based method for predicting the flow field and flow-driven rotation of a vertical-axis hydrokinetic turbine operating in previously unseen free-stream velocities. A Convolutional Neural Network (CNN) is trained and tested using the solutions of five two-dimensional (2-D), foil-resolved Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations, with free-stream velocities of 1.0, 1.5, 2.0, 2.5, and 3.0 m/s. Based on the boundary conditions of free-stream velocity and rotor position, the flow fields of x-velocity, y-velocity, pressure, and turbulent viscosity are inferred, in addition to the angular velocity of the rotor. Three trained CNN models are developed to evaluate the effects of (1) the dimensions of the training data, and (2) the number of simulations used as training cases. Reducing data dimensions was found to diminish mean relative error in predictions of velocity and turbulent viscosity, while increasing it in predictions of pressure and angular velocity. Increasing the number of training cases from two to three was found to reduce relative error for all predicted unknowns. With the best achieved CNN model, the variables of x-velocity, y-velocity, pressure, turbulent viscosity, and angular velocity were inferred with mean relative errors of 6.93%, 9.82%, 10.7%, 7.48%, and 0.817%, respectively.

Experimental and multiphase modeling of small vertical-axis hydrokinetic turbine with free-surface variations

Vertical-axis hydrokinetic turbines are promising option to harness the low velocity currents. However, limited investigations have been carried out considering the interactions between the turbine rotor and the channel section, including the free-surface. Thus, a vertical-axis turbine model has been designed and manufactured, to be tested in an open channel. Also, a three-dimensional multiphase simulation has been carried out, using the volume of fluid (VOF) model, to capture the air–water interface and to investigate the free-surface variations effects on the turbine output. Experimentally, the turbine model has been characterized under different flow conditions and free-surface levels. The peak power coefficients are found to increase with the upstream velocity. This effect is directly linked to the blockage ratio and the Froude number. A reasonably good match has been found between the experimental and the numerical results. The VOF model is able to simulate the free-surface longitudinal variations, and the effect of the turbine blockage of the channel. The velocity field and the pressure coefficient distribution, around the turbine rotor, have been studied and correlated with the free-surface variations from upstream to downstream of the turbine. Finally, the vortex street generated by the blade–plate interaction has been analyzed.

Numerical simulations of a vertical-axis hydrokinetic turbine with different blade-strut configurations under free-surface effects

Numerical simulations of a vertical-axis hydrokinetic turbine with different blade-strut configurations under free-surface effects

Experimental Investigation of the Effect of Passive Flap Configuration on the Performance of the Darrieus Hydrokinetic Turbine at Low TSR

The finite supply of fossil fuels has forced scientists to explore sustainable energy alternatives. One of the alternatives is using a hydrokinetic turbine to generate energy from the water current. Vertical axis hydrokinetic turbine Darrieus type has a range operation in medium to high TSR. In this study, a Darrieus hydrokinetic turbine was tested experimentally in lower TSR to observe the behavior of the attached passive flap on the turbine's blade with different placement configurations, i.e., inner flap, outer flap, and combined flap. The passive flap movements were limited to a maximum opening angle of 45° and 90° for each flap position compared to NACA 0018 (Clean) without a flap. The test was demonstrated inside the racetrack flume under Re 14500. All the tests were recorded using a video camera to give clear information regarding the flap's behavior. The turbine torque was measured using a rope brake dynamometer by gradually adding weights to create resistance between the rope and the turbine's rotation. As a result, the inner flap configuration with a maximum opening angle of 90° positively affects the turbine performance compared to all configurations. Attaching a passive flap outside the blade rotation will reduce the turbine performance. The smaller the opening angle of the outer flap, the higher the turbine performance and vice versa. It indicates that the outer flap for Darrieus hydrokinetic turbine is not recommended. Furthermore, the inner flap improves the operation range in lower TSR than the original NACA 0018.

Performance analysis of dual-stage vertical axis hydrokinetic turbine (VAHT) with azimuth variation at open canal hydrokinetic power plant

For several decades, the use of hydropower generation using hydrokinetic turbines has grown rapidly, aiming to get energy alternatives and reduce the dependency on fossil energy. Despite it has low efficiency, the vertical axis hydrokinetic turbine (VAHT) has been used to utilize hydro energy and has a promising result. A previous study had stated that the utilization of cascaded blade enhances the performance of VAHT. However, this technology produces fluctuating torque and power during its rotation. Hence the dual-stage VAHT is proposed to overcome this issue to improve VAHT’s efficiency. This research analyzes the dual-stage VAHT’s performances by variating its inter-stage azimuth of 45°, 60°, 75°, and 90°. For each stage, there is six blades that attach at three arms. The computational fluid dynamics (CFD) simulation is employed as its capability to provide in-depth information regarding flow phenomenon, force, and torque. This simulation has proven that the dual-stage configuration has an impact on reducing torque fluctuation of VAHT and show that different of inter-stage azimuth angle brings to different torque fluctuation pattern. The average torque value produced by the new turbine with variations in shift between stages of 45°, 60°, 75° and 90° is 10,119.21 Nm, 10,656.13 Nm, 10,490.31 Nm, and 10,457.3 Nm, respectively.

Structural Strength Study for Vertical Axis Hydrokinetic Turbine Frame

One of the renewable energy sources is ocean currents which can be extracted with the Darrieus vertical axis hydrokinetic turbine (VAHT). This research aims to analyze the deformation and structural stresses that occur in the Darrieus VAHT support frame due to the loads. In the VAHT installation, it is necessary to have a support structure in the form of a solid frame, so that the turbine remains in a stable condition when operating. The VAHT frame must be able to withstand the load from a rotating turbine and have a small drag force. This study conducted a numerical simulation using the finite element analysis method. The effect of the cross-sectional shape of the structural beams on the drag due to flow was also investigated. The result is the frame designed with the ASTM A36 Grade B pipe structure has maximum stress of 63,116 MPa and it is relatively smaller and remains within the safe limits of the material. In addition, based on CFD simulation, the drag caused by the flow across the structure with this design is also smaller. Therefore, this study can be used as a consideration in making decisions to design the Darrieus VAHT frame.

Synthetic jets as a flow control device for performance enhancement of vertical axis hydrokinetic turbines: A 3D computational study

In the present work, a vertical axis turbine with straight blades was analyzed through a numerical simulation in three dimensions, the performance of the turbine was studied while synthetic jets were used as an active flow control method. To carry out the simulations, the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations were solved on Star CCM+, through the k-ω SST turbulence model. The dynamics of the turbine movement were described using the Overset Mesh technique, capturing the transient characteristics of the flow field. Hydrodynamic coefficients and vorticity fields were obtained to describe the flow behaviour, and the results were compared with two-dimensional simulations of the same system. Turbine performance with tangential synthetic jets located on the intrados and extrados of the airfoil shows an increase in the torque and power output of the turbine. Moreover, using simple estimates, synthetic jets used less power than the increment in power generated at the turbine shaft, showing that efficiency of the turbine increases with the use of synthetic jets. However, the increment in the turbine performance is not as high as in previous two-dimensional studies reported in the literature.

Performance and near-wake analysis of a vertical-axis hydrokinetic turbine under a turbulent inflow

This study investigates the performance and near-wake characteristics of a full-scale vertical-axis hydrokinetic turbine under a uniform inflow and turbulent inflow with a 5% and 10% turbulence intensity. The governing equations of the flow field are the incompressible Navier–Stokes equations expressed within an arbitrary Lagrangian–Eulerian framework to account for mesh motion. To discretize the system of equations, the residual-based variational multiscale formulation, augmented with a weakly imposed Dirichlet boundary condition at no-slip surfaces, is used. Moreover, a turbulent inflow is prescribed using a synthetic turbulence generation method referred to as Smirnov’s random flow generation and the near-wake characteristics are studied using a multi-domain method. While the performance of the turbine slightly reduced under a turbulent inflow compared to a uniform inflow, there was a negligible difference in its performance between the two turbulent inflow conditions. A turbulent inflow also resulted in large fluctuations of the instantaneous power coefficient which has important implications for the fatigue life of certain components. Lastly, the wake recovery was notably improved under a turbulent inflow suggesting that a shorter streamwise inter-device spacing may be acceptable in highly turbulent tidal sites.

Some effects of turbine inertia on the starting performance of vertical-axis hydrokinetic turbine

Straight-bladed vertical-axis hydrokinetic turbines have a number of advantages for power extraction from river, tidal, and ocean currents. They are simple to construct, the generator does not need to be submerged, and they can have good power extraction efficiency. Among their potential disadvantages is that when the load is lost, or when they start with no load, they can reach high instantaneous blade speeds before returning to a “steady” runaway speed. These high speeds can cause high loads on the blades and must, therefore, be fully understood. This paper describes a computational investigation of the effect of inertia as a turbine starts from rest with no load and reaches runaway. Turbine inertia is modified by altering the blade density while the turbine geometry is not altered. At the minimum inertia, the added mass contributes significantly to the dynamics, and the highest overshoot occurs in blade speed. Increasing inertia damps the peak but slows the acceleration. The added mass depends on blade mass but is constant for the whole starting sequence and is independent of water speed. The results give guidance for the design of turbines to balance the minimization of the overshoot and starting time.

Performance enhancement of vertical axis hydrokinetic turbine using novel blade profile

Savonius hydrokinetic turbine is a promising technology for small-scale hydropower generation. The savonius turbine has a simple design and good starting characteristics but suffers from poor performance. In this study, a novel blade profile has been proposed to improve the performance of the conventional savonius turbine rotor. The new blade profile is based on a S1048 airfoil section. The geometry of S1048 airfoil section blades is composed of straight and curved segments. The long straight edge provides larger moment arm and gap flow while the curved segment decreases the effect of negative torque on the rotor. Unsteady RANS CFD simulations have been performed to evaluate and compare the performance of the proposed blade profile. It is shown that the maximum power coefficient of the conventional design can be improved by 14% at a tip speed ratio of 1, by using the new blade profile. The performance of the proposed design has also been evaluated by augmenting an upstream curtain arrangement with the turbine. As a result, an additional 13% increase in the power coefficient was realized when compared with the conventional augmented rotor.

Hydrodynamic performance of vertical axis hydrokinetic turbine based on Taguchi method

Hydropower generation is an important part of global renewable energy development. The vertical axis hydrokinetic turbine (VAHT) is a typical device to capture the kinetic energy of water. The optimization of its hydrodynamic performance can improve power coefficient. In this study, the Taguchi method was used to optimize the typical parameters of the vertical axis turbine, i.e., airfoil (NACA), pitch angle (β), enwinding ratio (ϖ), solidity ratio (σ), and small shaft position (O). An orthogonal array with five parameters and four levels was established; then, sixteen runs were simulated using computational fluid dynamics (CFD) software. A signal-to-noise (S/N) ratio analysis of the CFD simulation results was carried out, and the hydrodynamic performance of the optimized VAHT was studied. The results show that the influence strength order of each parameter on the power coefficient of the VAHT is featured by the relation NACA >σ > O > ϖ > β. According to the S/N ratio, the optimal combination of the five factors is as follows: NACA = 0020, β = 0°, ϖ = 1.25, σ = 0.382, and O = 0.5. In comparison with the initial design, the optimized minimum self-starting torque coefficient of the turbine is increased by 15.9%, which means that the self-starting performance is optimized. The power coefficient (CP) of optimized turbine is 0.1951, which is 17.59% higher than in the initial design, and the power coefficient fluctuation is 87.56% lower. Finally, the research findings could provide a reference for the optimal design of vertical axis turbines.

Development of a desmodromic variable pitch system for hydrokinetic turbines

The use of vertical-axis turbines is raising interest in the field of hydropower production from rivers or water channels, where suitable mass flows are available, without the need of high water jumps or large construction sites. Like their wind-based counterparts, these machines have many advantages in terms of installation and maintenance, but suffer from an inherently complex rotor hydrodynamics, characterized by a continuous variation of the blade angle of attack beyond the static stall limit and the corresponding onset of dynamic instabilities. In virtue of their typically lower rotational speed nonetheless, hydrokinetic machines can benefit from the possibility of active blade pitch control, which is barely feasible in case of wind turbines due to their high characteristic operation frequencies. Moving from this background, a novel control strategy, based on a double-cam desmodromic pitching system, has been developed in the present study by means of a combination of medium- and high-fidelity numerical approaches. In order to tailor the corresponding pitching law, here implemented in a parametric form, to this class of machines, a dedicated automatic optimization framework has been developed in the ANSYS® WORKBENCH® 20.2 suite. The latter combines a Multi-Objective Genetic Algorithm (MOGA) optimizer with an advanced two-dimensional Actuator Line Model (ALM) model of the turbine, developed by the authors. This optimization approach has then been applied to a test rotor with the objective of maximising the turbine power coefficient while containing the rotor stream- and cross-wise force oscillations. The resulting optimal configurations have been eventually verified via high-fidelity, fully-resolved CFD simulations. Results show that variable pitch can represent a promising solution for increasing the performance of vertical-axis hydrokinetic turbines, leading to a +35% efficiency enhancement as well as to a reduction of the machine unsteady loads.