Horizontal Axis Hydrokinetic Turbine Research Articles

Wake characteristics in high solidity horizontal axis hydrokinetic turbines: a comparative study between experimental techniques and numerical simulations

Wake characteristics in high solidity horizontal axis hydrokinetic turbines: a comparative study between experimental techniques and numerical simulations

Structural Analysis of a First, Second and Third Generation Horizontal Axis Hydrokinetic Turbine

The objective of this work is to evaluate through computational simulation the structural integrity of a horizontal axis hydrokinetic turbine (HAHKT) when using various geometric configurations of diffusers. This study was carried out by fluid -structure interaction (FSI) sing Ansys Workbench V18.2, coupling CFX and mechanical structural, in which a structural analysis was carried out based on the results obtained at the hydrodynamic level of a HAHKT composed of three blades with profile NREL S822, which was also analysed under the implementation of two geometric diffuser configurations. The maximum stresses in the blades increase of 27 % using the third-generation diffuser.

Torques and Moments of Inertia Models for Horizontal Axis Hydrokinetic Turbine Driveline

The quantification of torques and moments of inertia of horizontal axis hydrokinetic turbine driveline is important to precisely predict the dynamic behavior of the complete system. Initially, this paper presents different models used in the literature for describing torques and moments of inertia of turbine components. A dynamic model of a small hydrokinetic turbine using belt transmission is developed. The model uses the Blade Element Momentum (BEM) for determining the power coefficient of the turbine rotor and considers the inertial effects and dissipative torques of whole system using some of the torque models and moments of inertia described previously. The results for the dynamical behavior of the turbine model are compared with experimental data, showing good agreement. In order to numerically analyze a more efficient drivetrain, the belt transmission is replaced by a planetary gearbox in the dynamic model, and the new results are also assessed. As a result, it was found that with planetary gears, a more compact transmission can be used, reducing the inertial effects, which brings a better efficiency in the starting of the machine and shortening the transient regime time.

Assessment of a Diffuser-Augmented Hydrokinetic Turbine Designed for Harnessing the Flow Energy Downstream of Dams

Harnessing the remaining energy downstream of dams has recently gained significant attention as the kinetic energy available in the water current is considerable. This work developed a novel study to quantify the energy gain downstream of dams using a horizontal-axis hydrokinetic turbine with a diffuser. The present assessment uses field data from the Tucuruí Dam, where a stream velocity of 2.35 m/s is the velocity at which the highest energy extraction can occur. In this case, a 3-bladed hydrokinetic turbine with a 10 m diameter, shrouded by a flanged conical diffuser, was simulated. Numerical modeling using computational fluid dynamics was carried out using the Reynolds averaged Navier–Stokes formulation with the κ – ω shear stress transport as the turbulence model. The results yield good agreement with experimental and theoretical data available in the literature. Moreover, the turbine power coefficient under the diffuser effect could increase by about 55% for a tip speed ratio of 5.4, and the power output increased by about 1.5 times when compared to the same turbine without a diffuser. Additionally, as there are no hydrokinetic turbines installed downstream of dams in the Amazon region, the present study is relevant as it explores the use of hydrokinetic turbines as an alternative for harnessing the turbined and verted flow from dams. This alternative may help avoid further environmental impacts caused by the need for structural extensions.

Design and economic analysis of a hydrokinetic turbine for household applications

Social and political concerns on climate change have made renewable energy an essential component of government’s work plans. Grid-connected horizontal-axis hydrokinetic turbines are promising eco-friendly power sources for electrical energy supply to households near middle-to-high discharge rivers, while providing an opportunity to sell the energy surplus. In this work, a rotor design analysis of a hydrokinetic turbine with a 1 m nominal radius is performed based on blade element momentum theory. Then, an economic analysis is presented in terms of the discounted payback period and the internal rate of return. The numerical results show that three-bladed hydrokinetic turbines with a nominal tip speed ratio of 5 and state-of-the art high lift-to-drag ratio hydrofoils (∼100) lead to maximum performance with a power coefficient around 0.45. Performance can be further improved in an affordable manner using diffuser-augmented hydrokinetic turbines. The use of hydrokinetic energy in household applications can be profitable in leading economic countries with a discounted payback period of 4–6 years. In energy developing countries, this technological solution can be cost effective accompanied by economic subsides and implementation of a local industry, resulting in similar payback periods.

Comprehensive Parametric Study of Blockage Effect on the Performance of Horizontal Axis Hydrokinetic Turbines

When a hydrokinetic turbine operates in a confined flow, blockage effects are introduced, altering the flow at and downstream of the rotor. Blockage effects have a significant effect on the loading and performance of turbines. As a result, understanding them is critical for hydrokinetic turbine design and performance prediction. The current study examines the main and interaction effects of solidity (σ), tip speed ratio (TSR), blockage ratio (ε), and pitch angle (θ) on how the blockage influences the performance (CP) of a three-bladed, untwisted, untapered horizontal axis hydrokinetic turbine. The investigation is based on validated 3D computational fluid dynamics (CFD), design of experiments (DOE), and the analysis of variance (ANOVA) approaches. A total number of 36 CFD models were developed and meshed. A total of 108 CFD cases were performed as part of the analysis. Results indicated that the effect of varying θ was only noticeable at the high TSR. Additionally, the rate of increment of CP with respect to ε was found proportional to both TSR and σ. The power and thrust coefficients were affected the most by σ, followed by ε, TSR, and then θ.

Numerical Investigation of the Performance, Hydrodynamics, and Free-Surface Effects in Unsteady Flow of a Horizontal Axis Hydrokinetic Turbine

This paper presents computational fluid dynamics (CFD) simulations of the flow around a horizontal axis hydrokinetic turbine (HAHT) found in the literature. The volume of fluid (VOF) model implemented in a commercial CFD package (ANSYS-Fluent) is used to track the air-water interface. The URANS SST k-ω and the four-equation Transition SST turbulence models are employed to compute the unsteady three-dimensional flow field. The sliding mesh technique is used to rotate the subdomain that includes the turbine rotor. The effect of grid resolution, time-step size, and turbulence model on the computed performance coefficients is analyzed in detail, and the results are compared against experimental data at various tip speed ratios (TSRs). Simulation results at the analyzed rotor immersions confirm that the power and thrust coefficients decrease when the rotor is closer to the free surface. The combined effect of rotor and support structure on the free surface evolution and downstream velocities is also studied. The results show that a maximum velocity deficit is found in the near wake region above the rotor centerline. A slow wake recovery is also observed at the shallow rotor immersion due to the free-surface proximity, which in turn reduces the power extraction.

Performance evaluation of high-lift hydrofoils with a flap used in the design of horizontal-axis hydrokinetic turbines

The hydrodynamic performance and the flow field of two horizontal-axis hydrokinetic turbines with and without a high-lift hydrofoil with a flap were investigated using computational fluid dynamics (CFD) simulation. For improving the accuracy of the numerical simulation, the user-defined function (UDF) of 6-degrees of freedom (6-DoF) was used in the Ansys Fluent software. Unsteady Reynolds-averaged Navier–Stokes (URANS) equations coupled to the SST 𝑘 − 𝜔 turbulence model were employed during the simulation. A three-dimensional model of both of the turbines with three blades was conducted for obtaining the performance curve of the power coefficient (𝐶𝑃) versus the tip speed ratio (TSR). The maximum power coefficients (𝐶𝑃𝑀𝑎𝑥) of the hydrokinetic turbines with and without a high-lift hydrofoil arrangement were 0.5050 and 0.419, respectively. Experimental data from the literature were used for the validation of the numerical results, specifically for the case when a rotor with traditional blades is utilized. In general, the simulation results were in good agreement with the experimental data.

Numerical and experimental study of hydrofoil-flap arrangements for hydrokinetic turbine applications

In this work, the efficiency of two horizontal-axis hydrokinetic turbines, whose blades were designed with and without multi-element hydrofoil cross-sections, has been numerical and experimentally investigated for tip speed ratio (λ) values ranging between 2.5 and 9.0 to compare the experimental rotor performance with numerical results. The Eppler 420 hydrofoil was used for the design of the blades applying the blade element momentum (BEM) theory. The variation of the power coefficient curve of the turbines was analyzed by using computational fluid dynamics (CFD) and experimental tests through ANSYs Fluent software with six-degrees of freedom (6-DoF) user-defined function (UDF) method and an open hydraulic channel, respectively. Numerically, for the turbine with a multi-element hydrofoil and without a multi-element (traditional) hydrofoil, maximum power coefficients (CPmax) of 0.5050 and 0.419 (at a λ value equal to 7.129 and 6.739, respectively) were obtained. It is worth noting that a reasonable agreement between the numerical and the experimental results was achieved. In this regard, the blade with a multi-element hydrofoil has a positive influence on the hydrokinetic turbine performance; therefore, it can be used for power generation in river or marine systems.

Surrogate-Based Optimization of Horizontal Axis Hydrokinetic Turbine Rotor Blades

A design method was developed for automated, systematic design of hydrokinetic turbine rotor blades. The method coupled a Computational Fluid Dynamics (CFD) solver to estimate the power output of a given turbine with a surrogate-based constrained optimization method. This allowed the characterization of the design space while minimizing the number of analyzed blade geometries and the associated computational effort. An initial blade geometry developed using a lifting line optimization method was selected as the base geometry to generate a turbine blade family by multiplying a series of geometric parameters with corresponding linear functions. A performance database was constructed for the turbine blade family with the CFD solver and used to build the surrogate function. The linear functions were then incorporated into a constrained nonlinear optimization algorithm to solve for the blade geometry with the highest efficiency. A constraint on the minimum pressure on the blade could be set to prevent cavitation inception.

Coaxial horizontal axis hydrokinetic turbine system: Numerical modeling and performance optimization

Hydrokinetic turbines extract energy from free-flowing water, such as river streams and marine currents. For river applications, the typical deployment location is highly space-constrained due to both the nature of the river (i.e., its natural width and depth) and the other usages of the river. Therefore, a modified design of a conversion device is desired to accommodate these space limitations. The objective of this work is to derive optimum design criteria for a coaxial horizontal axis hydrokinetic turbine system utilizing both numerical and experimental approaches. Single-turbine systems configured with different sizes of untwisted untapered blades were numerically studied to obtain the optimum solidity and to examine the blockage effects on the various-solidity rotors. The numerical modeling was, then, extended to analyze the performance of the coaxial multi-turbine system (equipped with optimum-solidity rotors) and characterize its ambient flow. The numerically predicted power outputs were validated against those measured with torque and rotational speed sensors in a water tunnel for both single-turbine and multi-turbine systems. Particle image velocimetry was also utilized to evaluate the wake structure and validate the numerical results of the flow characteristics. The optimum-solidity for the single-turbine system was found to be 0.222 48. An optimum-solidity three-turbine axial system can increase power output by 47% when compared to an optimum-solidity single-turbine system. Increasing the number of rotors from three to five only enhanced efficiency by about 4%. The study of wake structures behind a three-turbine system showed that the highest velocity deficit occurs behind the second rotor rather than the third rotor.

Numerical analysis on the use of multi-element blades in a horizontal-axis hydrokinetic turbine

The blades of a hydrokinetic turbine have a great impact on its performance due to they are the elements responsible for capturing the kinetic energy from water and transform it into rotational mechanical energy. In this work, numerical analyses on the performance of a multi-element blade section were developed. The lift and drag coefficients (CL and CD, respectively) of the hydrofoils with traditional and multi-element configurations were studied. For this purpose, 2D numerical analyses were conducted by using JavaFoil code. S805, S822, Eppler 420, Eppler 421, Eppler 422, Eppler 423, Eppler 857, Wortmann FX 74-CL5-140, Wortmann FX 74-CL5-140 MOD, Douglas/Liebeck LA203A, Selig S1210, Selig S1223 and UI-1720 profiles were tested. The results indicated that the Eppler 420 multi-element hydrofoil provided high efficiency to the turbine. This was attributed to its higher relationship between the maximum CL and CD (CLmax /CD), which was equal to 47.77, compared to that of the Selig S1223 profile (39.59) and other hydrofoils studied. Therefore, the final optimized blade section selected was an Eppler 420 multi-element hydrofoil with a flap chord length of 70% of that of the main profile. The hydrodynamic and structural designs of the optimized blade section were validated with detailed 3D numerical models, through ANSYs Fluent software. The fluid and structural domains were connected using one-way coupling. The influence of the blade geometry and the operational parameters on the stresses supported by the blades were found by analyzing the fluid-structure interaction. From the numerical analyses conducted, it was observed that the blades did not exhibit structural fails. In this regard, the multi-element hydrofoil might be used for the design of a horizontal-axis hydrokinetic turbine with a high efficiency.

On the upscaling approach to wind tunnel experiments of horizontal axis hydrokinetic turbines

In this work, we proposed an upscaling methodology to extrapolate results from wind tunnel experiments with small-scale model to the full-size hydrokinetic turbine. Small-scale 1:20 wind tunnel experiments ( $${\hbox {Re}}\sim 10^4$$ ), with a three-blade horizontal axis turbine, were carried out looking to identify the characteristic curves of a full-size turbine operating in water ( $${\hbox {Re}}\sim 10^6$$ ). The lack of dynamic similarity due to unmatched Reynolds numbers is analyzed in the framework of blade element momentum theory arguments. A new semi-empirical power-law equation is achieved, uniquely based on the BEM theory which relates the power coefficients of model and full-size turbine to the Reynolds numbers and a power factor, specific to each turbine. Computational fluid dynamic CFD simulations for the same rotor geometry, simulating different runners with varying diameters from small-scale model to full-scale turbine are carried out to validate the upscaling arguments, and to verify the accuracy of the power coefficient curves predicted by proposed methodology.

Experimental evaluation of coaxial horizontal axis hydrokinetic composite turbine system

Hydrokinetic energy conversion systems are emerging as a viable solution for harnessing kinetic energy. However, the typical deployment location is highly space-constrained due to both the nature and the other uses of the river. Therefore, a modified conversion device to overcome these constraints is necessary. The research objective of this work was to evaluate and enhance the performance of multiple coaxial horizontal axis hydrokinetic turbines (HAHkTs) mounted on a single shaft. The hydrodynamic performance of different configurations of single- and multi- HAHkTs with blades made of carbon fiber polymer composites was evaluated in a water tunnel. Increasing the number of rotors of the turbine system from one to two enhanced efficiency by approximately 75% and lowered the operational tip speed ratio. The third rotor also enhanced the efficiency, but the improvement was less (about 32%) due to the slower flow passing this rotor. A duct reducer was also incorporated, and its effect was studied. Finally, the wake behavior and its effect on the multi-turbine system operation were examined by using a particle image velocimetry system. From the structure aspect, composite materials have the appropriate properties that suit the water turbine blades. The composite blades were manufactured using the out-of-autoclave process.

Design and Optimization of a Diffuser for a Horizontal Axis Hydrokinetic Turbine using Computational Fluid Dynamics based Surrogate Modelling

Fossil fuels have remained at the backbone of the global energy portfolio. With the growth in the number of factories, population, and urbanization; the burden on fossil fuels has also been increasing. Most importantly, fossil fuels have been causing damage to the global climate since industrialization. The stated issues can only be resolved by shifting to environment friendly alternate energy options. The horizontal axis hydrokinetic turbine is considered as a viable option for renewable energy production. The aim of this project is the design and optimization of a diffuser for horizontal axis hydrokinetic turbine using computational fluid dynamics based surrogate modeling. The two-dimensional flat plate airfoil is used as a benchmark and flow around the airfoil is simulated using Ansys Fluent. Later, computational fluid dynamics analyses are carried out for baseline diffuser generated from the flat plate airfoil. The performance of this diffuser was optimized by achieving an optimum curved profile at the internal surface of the diffuser. The response surface methodology is used as a tool for optimization. A maximum velocity augmentation of 31.70% is achieved with the optimum diffuser.

Experimental evaluation of a shrouded horizontal axis hydrokinetic turbine with pre-swirl stators

Improving the efficiency and power output of hydrokinetic turbines is critical to making them a viable and cost-effective renewable energy solution. Diffusing shrouds have already been shown to improve the performance of horizontal axis, axial-flow turbines. It has been suggested that adding pre-swirl stators to the shroud could alter the inlet flow so as to maximize net tangential force on the turbine blades, thus increasing power output. There is a scarcity of published physical model test data from pre-swirl stator turbines. The present study explores this concept. Four different pre-swirl stator configurations were designed and tested on a shrouded 3-bladed turbine (26.54 cm diameter) in the 36.5 m towing tank at the United States Naval Academy. Three Reynolds numbers (6.07×104, 8.10×104, and 1.01×105 based on stator chord length), corresponding to flow speeds 0.91 m/s, 1.22 m/s, and 1.52 m/s respectively, were tested. At the lowest Reynolds number, all 4 stator configurations improved the maximum Cp by 5–23% compared to the turbine with shroud only. At the middle and highest Reynolds numbers, the stator effect was mostly neutral, with one configuration showing a negative effect at the highest Reynolds number (i.e., lowered the maximum Cp). These results indicate that pre-swirl stators have the potential to improve turbine performance, particularly at lower Reynolds numbers, where the flow is more laminar and the absolute velocities are lower (for a given blade dimension). Pre-swirl stators also appear to reduce the dependence of performance on Reynolds number, flattening the curve and allowing optimal performance over a wider range of operating conditions. Further analytical and computational studies are recommended to explore these findings further, and to develop broader guidance on when pre-swirl stators are advantageous.

Development of a semi-analytical model to select a suitable airfoil section for blades of horizontal axis hydrokinetic turbine

All modern hydro-kinetic turbines are being designed based on a lift, using airfoils, which should have a significant lift to drag ratio to achieve maximum efficiency.SG604X family airfoil has significant lift-to-drag ratio under an operating range of Re from 105–106, which also come under our working conditions. Blade Element Momentum (BEM) theory was used to obtain optimum blade shape. The iterative numerical approach was used in MATLAB to calculate optimized blade profile and coefficient of performance (Cp). After grid independency test, finally k-ω shear stress transport (SST) and the k-є model with enhanced wall treatment were used for calculation of the lift coefficient and the drag coefficient of airfoil SG6043. The performance of the rotor overall expected tip speed ratio (T.S.R (λ)) was calculated and found that maximum Cp,max is 0.51 at optimum λopt of 5. The suitability of SG6043 airfoil over NACA0012 airfoil in our case has been shown.

Performance characteristics of shrouded horizontal axis hydrokinetic turbines in yawed conditions

During operations, river and tidal hydrokinetic turbines encounter changes in flow direction that decrease their performance. Evaluating hydrokinetic turbines in yaw conditions contributes to estimating turbine performance, power stability, and power delivered to the grid. Water tunnel tests using a 19.8 cm diameter horizontal axis model turbine in yaw operation show the performance reduction using three designs: no shroud, a convergent-divergent shroud, and a diffuser shroud. Experimental results obtained at three Reynolds numbers of 1.38 × 105, 1.77 × 105, and 2.17 × 105 show that the output power decreases in off-axis flows for all designs investigated. The reduction is initially negligible up to a 10° yaw angle, but then increases with increasing the yaw angle. The convergent–divergent shroud experiences significantly less performance loss compared to the other two designs. The maximum performance loss of the convergent-divergent shroud design is 6% on average for the Reynolds numbers investigated. Based on the experimental results and in analogy to the linear momentum theory cosine cubed rule, we propose new cosine relations for shrouded turbines in yaw operations. Depending on the shroud's geometry, the maximum power of a shrouded turbine decreases either with the cosine or the cosine squared of the yaw angle.

Hydrodynamic performance evaluation of a new hydrofoil design for marine current turbines

Tidal energy has clear potential in producing large amounts of energy as the world’s capacity exceeds 120 GW. Despite being one of the oldest renewable energy sources exploited by man, the technology is still in its pre-commercialisation stage and so lags behind other renewable sources such as wind and geothermal energy in terms of development and energy produced. One of the emerging energy extraction technologies in the tidal energy field is the Horizontal Axis Hydrokinetic Turbine (HAHT) which harness tidal stream energy the same way Horizontal Axis Wind Turbine (HAWT) extract energy from the wind. While HAHT has been the topic of many researches over the past decade, design of hydrofoils plays a vital role in increasing the structural strength of the blade and maximizing the output of the marine current turbines. In this context, a numerical investigation is conducted in this research in which new hydrofoil for marine current turbines underwater conditions was designed and evaluated. The turbine blade is designed using XFLR5 code and QBlade which is a Blade-Element Momentum solver with a blade design feature. Then, the hydrodynamic performance of hydrofoil was tested using Computational Fluid Dynamics (CFD) consisting of lift and drag coefficients, and velocities distribution. The results showed that the new design of the hydrofoil of marine current turbine blade maintained a CPower value of 50% more from normal range at the TSR 5 to 9 and 51% more at TSR = 6,5 in the performance curve.

Design and hydrodynamic analysis of horizontal-axis hydrokinetic turbines with three different hydrofoils by CFD

The conversion of kinetic energy that comes from low-head water currents to electrical energy has gained importance in recent years due to its low environmental and social impact. Horizontal axis hydrokinetic turbines are one of the most used devices for the conversion of this type of energy [1], being an emerging technology more studies are required to improve the understanding and functioning of these devices. In this context, the hydrodynamic study to obtain the characteristic curves of the turbines are fundamental. This article presents the design and hydrodynamic analysis for three horizontal axis tri-blade hydrokinetic turbine rotors with commercial profiles (NACA 4412, EPPLER E817 and NRELS802). The Blade Element Momentum (BEM) was used to design three rotors. The DesignModeler, Meshing and CFX modules from the ANSYS® commercial package were used to discretize the control volumes and configure the numerical study. In addition, Grid Convergence Index (GCI) analysis was performed to evaluate the precision of the results. The computational fluid dynamics (CFD) was used to observe the behavior of the fluid by varying the speed of rotation of the turbines from 0.1 rad s-1 to 40 rad s-1, obtaining power coefficient of 0.390 to 0.435. For a maximum shaft power of 105W. In addition, it is evident that for the same conditions the rotor designed with the EPPLER E817 profile presents better performance than built with the NACA4412 and NREL S802.