Hydrokinetic Turbine Research Articles

Influences of Yaw characteristics on the performance of an Archimedes screw hydrokinetic turbine

A system for in situ power generation that exploits deep-sea current energy has been developed to meet the electricity demands of deep-sea observational equipment. The Archimedes screw hydrokinetic turbine (ASHT) is notable for its self-starting capabilities and energy efficiency, making it well suited for deployment in the low-speed deep-sea environment. This study elucidates two distinctive hydrodynamic characteristics of ASHT and explicates the underlying operational principles for the first time. Specifically, the ASHT is capable of self-yawing without the need for auxiliary yawing mechanisms and, when fixed, can harness ocean currents from a wide array of directions. Based on these hydrodynamic characteristics, passive yaw and fixed installation methods are proposed. A rigorously validated numerical model, supported by water flume tests, is utilized to illuminate the real-time flow mechanisms and assess the effect of different geometric variables on the ASHT yawing performance. An in-house Simulink model evaluates the power supply capabilities of both installation options, revealing that fixed installations are preferable for locations with varied incoming flow angles, whereas passive yaw installations are more appropriate for sites with a restricted range of incoming flow angles.

Numerical Investigation of Savonius Hydrokinetic Turbine Having Novel Thick Blades.

Recently, hydrokinetic energy is playing an important role in the production of green energy. It boasts a minimal ecological footprint and holds significant promise for generating energy on a small scale. Savonius Hydrokinetic Turbine (SHKT) acquires the hydrokinetic energy and converts it into useful energy. It has some specific advantages over other hydrokinetic turbines. Two unique thick blade designs have been utilized to replace the traditional semi-circular blades of the Savonius hydrokinetic turbine, resulting in the creation of two novel variants known as SHKT Design-1 and SHKT Design-2. Numerical investigations are carried out to assess and contrast the performance of SHKT Design-1 and SHKT Design-2 with conventional SHKT, with inlet velocity 0.9 m/s at various tip speed ratios between 0.7 to 1.1. The current study demonstrates that, the performance of SHKT is greater compared to SHKT Design-1 and SHKT Design-2. Savonius hydrokinetic turbine has a 10.5% and 7.5% higher maximum coefficient of power compared to SHKT Design-1 and SHKT Design-2 respectively. The flow field generated about the SHKT, SHKT Design-1 and SHKT Design-2 are examined and deliberated upon to evaluate performance across different facets.

Preface of the proceeding of 11th International Symposium on Current Research in Hydropower Technologies

The international symposium on Current Research in Hydropower Technologies (CRHT) aims to bring the researchers and students from the field of hydropower around the world in a common platform to share their research experiences. Since 2018, we have also been publishing papers from this conference in IOP Journal of Physics.This year in the symposium, we received 41 papers from Kathmandu University (KU), Tribhuwan University (TU), Norwegian University of Science and Technology (NTNU), École Polytechnique Fédérale de Lausanne (EPFL), Indian Institute of Technology (IIT-Roorkee), IIT-Delhi and Gujarat Technological University, Uka Tarsadia University and CK Pithawala, Gujarat.In the symposium, the overall event was divided into three sessions. The first group of sessions contained hydraulic turbines as well as hydropower and other technologies. We had presentations related to computational and experimental techniques related to the turbines, as well as civil and environmental aspects of the power plants, including sediment traps, tunnels and finding solutions for fish friendly and sustainable power plants. In the second group, there were sessions related to other forms of renewable energies as well, such as fuel cells, hydrokinetic turbines as well as seismic assessment of structures in hydropower. In the third group, we witnessed presentations related to condition monitoring of turbines, erosion and cavitation problems and some interdisciplinary aspects of the sustainable development.After receiving comments from the presentations and a peer review process, 36 papers have been selected for publication in this proceeding. We hope that the papers will be beneficial for the researchers and students involved in the sector of hydropower.

Impact of Blade and Solidity on the Performance of H-Darrieus Hydrokinetic Turbines by CFD Simulation

Purpose: In the present work, the 2D design of H-Darrieus turbines with a diameter of 900 mm and NACA blades 0018, 0025, 2415, and 4415 has been carried out for the solidity values of 0,5; 1 and 1,5. In order to know its maximum performance. Method/design/approach: The 2D simulations were developed with the ANSYS® FLUENT package in the transient state, varying the angular velocity (ω) for a peak velocity ratio (TSR) of 1 to 7 and the SST K-ω turbulence model, for a constant water flow rate of 1 m/s. This in order to know the results of the torque (Nm) generated and thus calculate the power coefficient (Cp). Results and conclusion: The NACA 0018 blade reached a power coefficient of 0,604 for a solidity of 0,5, followed by NACA 2415 blade at the same solidity with a maximum Cp of 0,594. On the other hand, the NACA 0025 blade for solidity of 1 reached a maximum Cp value of 0,570, while the NACA 4415 profile with a solidity of 1,5 obtained a maximum value of 0.495. Research implications: These results of maximum Cp values were given in a TSR range of 2 to 4 with a mean value of 3,5 for NACA profiles 0018 and 2415. Thus, evidencing the behavior of this type of turbine reaching maximum values to then begin to decrease. Originality/value: The present work contributes to the understanding of the impact of geometrical parameters on the operating coefficient of H-Darrieus.

Numerical analysis on the torque characteristics of hybrid hydrokinetic turbine for different configurations and operating conditions

A hybrid hydrokinetic turbine can become an efficient converter to harness the untapped hydrokinetic energy of small-scale hydro potentials sites such as canals and rivers, determining the optimal performance parameters becomes necessary. As the torque of a hydrokinetic turbine is considered one of the important performance parameters, an extensive numerical investigation has been carried out to analyse the torque characteristics of a hybrid HKT having a different value of radius ratio and attachment angle operated under different RPM and flow velocity. Under the present study, CFD analysis of four different configurations of hybrid hydrokinetic turbines covering the range of radius ratio from 0.2 to 0.8 and attachment angle from 30° to 150° have been carried out. A URANS with the conjunction of RNG k-ε has been exercised to accomplish the objectives of the present investigation. Based on the numerical results, the best configuration is found to have an optimum radius ratio value and attachment angle obtained as 0.4 and 90°, respectively. For the best-configured hybrid HKT, the average torque developed is improved by 51%, 20%, 19%, 6% and 24% compared to other hybrid configurations, corresponding to a TSR of 0.9 and Reynolds number of 1.12 × 105. The self-starting characteristics of the hybrid configuration with a 0.4 radius ratio and 90° attachment angle are better than the other considered hybrid configurations. Further, the instantaneous torque developed by the hybrid configuration with a 0.4 radius ratio and 90° attachment angle was found to be positive at each rotor angle during one cycle of revolution. Moreover, the least rate of torque pulsation is found for the hybrid HKTs operated at low RPM and Reynolds number.

CFD-based design optimization of ducted hydrokinetic turbines

Hydrokinetic turbines extract kinetic energy from moving water to generate renewable electricity, thus contributing to sustainable energy production and reducing reliance on fossil fuels. It has been hypothesized that a duct can accelerate and condition the fluid flow passing the turbine blades, improving the overall energy extraction efficiency. However, no substantial evidence has been provided so far for hydrokinetic turbines. To investigate this problem, we perform a CFD-based optimization study with a blade-resolved Reynolds-averaged Navier–Stokes (RANS) solver to explore the design of a ducted hydrokinetic turbine that maximizes the efficiency of energy extraction. A gradient-based optimization approach is utilized to effectively deal with the high-dimensional design space of the blade and duct geometry, with gradients being calculated through the adjoint method. The final design is re-evaluated through higher-fidelity unsteady RANS (URANS) simulations. Our optimized ducted turbine achieves an efficiency of about 54% over a range of operating conditions, higher than the typical 46% efficiency of unducted turbines.

Modeling and assessing the potential of the Boqueirão channel for tidal exploration

Exploring the energy potential of the oceans is a promising alternative to produce clean energy with a reduced environmental impact. Brazil has a significant tidal potential, particularly in the coastal region of the north, which covers the states of Amapá, Pará and Maranhão. The Boqueirão Channel, located in São Marcos Bay in Maranhão, is recognized for its wide tidal variability and strong tidal currents, which shows it has a significant tidal potential. This article examines the energetic characterization of this estuary in terms of tidal currents. Based on measurements taken in situ using an Acoustic Doppler Current Profiler and a Conductivity, Temperature and Depth sensor, the area is modeled in Delft3D software, with velocity results adjusted and validated to allow accurate representation of tidal currents. The theoretical potential of an area of 1.5 km2, considering a hydrokinetic turbine with diffuser, was estimated at 85.75 GWh. The results obtained are compared with those in the literature. Taking into account the available area and the physical constraints of the channel, it is possible to estimate a Levelized Cost of Energy - LCOE of 0.185 $kWh−1 for the projected hydrokinetic farm.

Design modification and performance prediction of ellipsoid cross-flow hydrokinetic turbine

In this study, an ellipsoid-shaped cross-flow hydrokinetic (ECFHKT) has been selected for the study. The performance of the ECFHKT was investigated for different design parameters, namely the number of blades, blade angle and blade length. The performance of ECFHKT was evaluated in terms of coefficient of torque (Ct) and coefficient of power (Cp) with respect to different tip speed ratios (TSR) by considering different flow velocities in the range of 0.5 m/s to 3.0 m/s, experimentally and numerically. Further, the Flow behavior across the ECFHKT was analyzed and discussed through pressure contour, velocity contour and velocity vector. It was found that design parameters play a vital role in enhancing the performance of the rotor and self-starting capabilities. For this analysis, the maximum Ct and Cp were obtained as 1.08 and 0.267, respectively. Further, It was observed that the ECFHKT performed well both in low and high flow conditions within a narrow range of tip speed ratio.

Design and performance investigation of a triple blade dual stage Savonius-alike hydrokinetic turbine from low flow stream reserves

ABSTRACT A trending technology that is being employed to generate hydro energy from low-flow stream reserves is the Savonius-alike hydrokinetic turbine (SAHT). Clearance between the stages of a dual-stage two-bladed SAHT was found to improve its performance at low flow speeds; however, the impact of clearance on the triple-bladed configuration of SAHT was not studied earlier. In this paper, a triple blade dual stage configuration of SAHT is designed, and its performance is investigated in a water flume under various stage clearances (0,5,10,15 and 20 mm), low flow speeds (0.45,0.55 and 0.65 m/s) and different brake loads. Detailed turbine performance under different design and off-design conditions are investigated to obtain meaningful performance insights. The findings show that torque production by the turbine increases with the increase of brake load, with maximum hydrodynamic torque generated at the highest brake load. The highest coefficient of performance and torque of 0.071 and 0.261 are obtained at a stage clearance of 5 mm, tip speed ratio of 0.273, and free-stream flow speed of 0.55 m/s. The present SAHT under design condition has improved performance compared to a dual blade dual stage SAHT exhibiting a wider tip speed ratio range for its application in low flow stream reserves. Further, this turbine may also be recommended for torque generation to work as a motor in a flow speed condition less than 0.5 m/s. The novelty of this work is the application of an additional flow control measure in the form of flow-through clearance to negotiate vertical water thrust through the clearance and exert additional pressure on the advancing blades of the SAHT in the upper stage.

The sustainable potential of hydrokinetic turbines in the Amazon basin

The Amazon, rich in biodiversity and natural resources, seeks renewable energy sources to minimize environmental impacts and reduce dependence on non-renewable sources. Hydrokinetic turbines emerge as a promising alternative by making it possible to convert the kinetic energy of river currents into electricity, without the need for dams. This study focuses on exploring the sustainable potential of hydrokinetic turbines in the Amazon region. For this, a prototype hydroelectric power plant that uses a hydrokinetic turbine was developed, and the feasibility of this technology as a renewable energy source was examined. The research included 3D modeling and propeller printing for the prototype, using materials such as carbon steel and 3D printing. The electrical components were dimensioned according to current technical standards, including cables, circuit breakers, batteries and converters. The methodology included tests on the real environment of a river in the Amazon region, evaluating the power generation capacity and the adaptability of the system to local conditions. The results demonstrated that the prototype is capable of producing electrical energy efficiently, taking advantage of the strength of river currents. The flexibility of the blades allowed adjustments according to the geometry of the watercourse, increasing the versatility of the system. In addition, the modular approach of turbines has shown promise for scalability and installation in different scenarios. This study contributes to the understanding of the potential of hydrokinetic turbines in the Amazon region, offering a renewable solution for electricity generation. The combination of technologies such as 3D printing, structural and electrical modeling has resulted in a prototype adaptable to local conditions, with the potential to provide clean energy to riverine communities, reducing dependence on non-renewable sources and promoting the sustainable development of the region.

Modeling of multi-phase, multi-fluid flows with applications to marine hydrokinetic turbines

In this paper, a numerical formulation for modeling turbulent multi-phase, multi-fluid flows over real-life marine devices is presented. The flow field is governed by the Navier–Stokes equations with an Arbitrary-Lagrangian–Eulerian (ALE) description of the continuum for handling independent domain movements. The multi-phase phenomenon is modeled for an iso-thermal homogeneous mixture of water vapor and liquid phases using a transport equation for the vapor volume fraction. The multi-fluid phenomenon is modeled using the level-set method where a geometric function, namely, the signed distance function (SDF) describes the level-set field. Turbulence modeling is handled in the context of the variational multiscale (VMS) method resulting in an ALE-VMS formulation for multi-phase, multi-fluid flows over moving hydrodynamic objects. Several augmentations to the formulation are discussed in this paper including the sliding interface (SI) operator and its role in enforcing the compatibility of solution fields between in-contact computational subdomains during the different steps of the solution. This formulation is validated against experimental data for a real-life horizontal-axis marine turbine under different flow conditions including single-phase flows, multi-phase flows and multi-fluid flows. The performance of the turbine as well as the expected flow behaviors are compared to the experimental data with success. An additional case is simulated for a multi-phase, multi-fluid flow condition showing the capabilities and robustness of the presented numerical formulation.

Transient starup performance of a micro horizontal axis river hydrokinetic turbine

Using the micro horizontal axis river hydrokinetic turbine to generate electricity is a low-cost power generation mode suitable for remote mountain areas. Startup performance is a key parameter related to annual power generation. Based on the numerical simulation, the influences of damping factor b, moment of inertia J, constant inflow velocity U and irregular inflow velocity (long-period and short-period inflow velocities) on the startup performance of a micro horizontal axis river hydrokinetic turbine are analyzed. Firstly, a decrease in b and J, as well as an increase in U, can reduce time required for startup. The increase of b and U cause the power coefficient Cp increase first and then decrease. The moment of inertia only affects the time required for startup, and has no impact on the Cp of the turbine in stable state. Secondly, for the long-period inflow velocity, an increase in T will result in a gradual increase in the average CP after the start-up is completed, however, the short-period has no significant effect on the mean value of each parameter. Finally, for the short-period inflow velocity, the fluctuation amplitude of hydrodynamic parameters decreases with T rising, but the fluctuation frequency increases.

A novel mechanism of turbulent kinetic energy harvesting by horizontal-axis wind and hydrokinetic turbines

We present a study on the influence of the turbulence generated by a cylinder on the performance of a free horizontal-axis turbine. The analysis focuses on the power coefficient, flow characteristics, and Turbulence Kinetic Energy (TKE) spectral density distribution. The mean velocity, turbulence intensity, and TKE are evaluated in the upstream and downstream planes of the turbine for configurations with and without the upstream cylinder. The results show that the power coefficient exhibits a peak when the rotor rotation frequency coincides with the frequency of vortex shedding from the cylinder, indicating a mechanism of conversion of TKE carried by large-scale structures into mechanical power. It was also observed that the turbine generates downstream turbulence in the absence of the cylinder but reduces the downstream turbulence when the cylinder is present. Spectral analysis of TKE confirms the influence of the frequency of vortex shedding on the velocity recovery of the turbine wake. The main contribution of this paper is the identification of a new mechanism of conversion of the TKE contained in large coherent turbulent structures into mechanical power. This study provides a further understanding of the complex phenomena involved in the interaction between the turbine and the upstream turbulent flow.

Effects of the spacing between two hydrokinetic turbines on the bedforms by numerical simulations

Accelerating hydrokinetic renewable energy development towards endurance requires investigating interactions between the hydrokinetic turbine and its surrounding physical environment. Interactions between hydrokinetic turbines (HT) and mobile sediment bed are considered as a critical area of assessment, however limited research studies have been published to address this issue. Hill et al. (2015) have shown experimentally that the presence of either single or multiple turbines and the rotation of the blades affect the bed morphology. Musa et al. (2019) have investigated experimentally the local effect of streamwise aligned turbines on the bedload, they found as a result that the geomorphic effects are stronger with increasing shear stress due to the presence of the rotors, inducing an alternating scour-deposition phenomenon. Chen et al. (2017) have investigated the influence of rotor blade tip clearance (distance between blades and seabed) on the scour rate of pile-supported horizontal axis current turbine. The results suggest that the decrease in tip clearance increases the scour depth, hence more sediment transport. Recently, Khaled et al. (2021) have studied the impact of hydrokinetic turbine on erodible sand banks, they showed numerically a significant interaction between the confinement of the turbine and its impact on the near bottom.
 
 In the present issue, we study the impact of two interacted turbines on the near bedform morphology. A modelling framework is derived to predict the significant transport induced by the turbines, such as the Euler-Euler (EE) multiphase model for sediment transport and the Blade Element Method (BEM) to model the forces generated by the turbines, using the open source platform OpenFOAM and the library SedFoam (Chauchat et al. 2017). A phase of validation is presented for the combined model (EE and BEM) using experimental results of Hill et al. (2015). The present study consists in considering one sediment class, sand of diameter of 0.25 mm, and two horizontal axis turbines with an axial flow direction corresponding to the riverine case. The approach is configured with four different axial inter-turbines distances. The wake distribution behind the second turbine is altered by the wake of the upstream turbine in all configurations (fig. 2). This interaction promotes the erosion under the turbines and the deposition along the axis of the turbines in the wake due to relation between the dynamics of ripples generation and the wake effects of turbines (fig. 3).

Conditional probabilistic encounter-impact model for fish-turbine interactions

Knowledge gaps exist in the collective effort to quantify risks and impacts of fish-turbine interactions. Empirical data and modeling studies have characterized stages of fish approach and pass through hydrokinetic turbines, but there has not been a comprehensive model that quantifies conditional occurrence probabilities of fish approaching and then interacting with a turbine in sequential steps. When calculating conditional probabilities, the probability of each step occurring is, in part, dependent on the occurrence of the previous step in the sequence. We combined acoustic data measurements and when data limited, published probabilities to estimate conditional probabilities of tidal turbine impacts on marine animals. The encounter-impact probability model includes approach, entrainment, and impact phases. The approach phase includes probabilities of entry into a spatial domain and zone of influence, followed by entrainment to the device. Each model component of an encounter includes probabilities of active or passive avoidance. Impacts are defined as fish collisions with a device, blade strikes by a rotating blade, and/or a collision followed by a blade strike. Probabilities are estimated using acoustic data from surveys in Admiralty Inlet, WA USA for Pacific herring (Clupea pallasii) encountering an axial or cross-flow turbine during day or night. Conditional probabilities are additive or multiplicative depending if events are cumulative or sequential. Impact probabilities for collisions and blade strikes are estimated individually and then combined to estimate the probability of overall impacts. Probabilities of occurrence for each model component range from 0.0000242 to 0.40. Impact probabilities for collision followed by a blade strike was lowest with estimates ranging from 0.0000242 to 0.0678. Impact probabilities for blade strike had the highest probabilities ranging from 0.000261 to 0.40. Overall impact probabilities had wide variability from 0.00110 to 0.689. Maximum probabilities occurred in each model component and overall impact probabilities for a cross-flow turbine at night with no active or passive avoidance. Estimates were lowest when probabilities were conditional on sequential events, and when active and passive avoidance was applied for an axial-flow turbine during the day. As expected, conditional probabilities were typically lower than equivalent model component and overall probabilities published in the literature. The encounter-impact conditional probability model can be applied to any marine animal in any environment for any hydrokinetic device. Estimating impact probabilities for Pacific herring in Admiralty Inlet for two device types illustrates utilization of existing data and simultaneously identifies data gaps needed to fully calculate empirical-based probabilities for any specific site-species scenario. As additional monitoring data are collected, accuracy of impact risks due to encounters of marine animals with hydrokinetic devices will increase and be confidently used in establishing regulatory policy.

Objective Functions for the Blade Shape Optimisation of a Cross-Flow Tidal Turbine under Constraints

Hydro-kinetic cross-flow tidal turbines (CFTT) are omni-directional and offer higher area-based power density compared to horizontal-axis tidal turbines, making them very attractive for tidal energy exploitation. However, the rotating motion around the vertical axis results in continuously varying angles of attack, causing alternating loads, which may lead to fatigue failure and structural damage. The OPTIDE Project addresses these challenges by implementing intracycle blade pitching to individually control the angle of attack, increasing the power coefficient CP and reducing structural loads. For this purpose a Darrieus turbine is designed with embedded actuators in each blade. Firstly a blade shape optimization will be conducted to fit the actuator at the quarter-chord position while ensuring sufficient thickness. The optimization procedure couples Computational Fluid Dynamics (CFD) with a Genetic Algorithm. The employed optimizer OPAL++ sets ten variables for each individual, which describe the hydrofoil shape, length and tip speed ratio (TSR). A smooth hydrofoil shape is generated from the variables, followed by an automatic mesh generation. Subsequently, numerical simulations of each individual at the desired TSR are conducted, while keeping the blade pitch angle constant. Simulation results provide the CP and stress acting on the turbine blades, which are the two optimization objectives (maximize CP while minimizing stress). This process is repeated during the optimization, aiming to determine the most suitable blade shape, that fits the actuator, and operating point (TSR) in a trade-off between CP and structural loads. This will lead to the increase of efficiency and a longer turbine lifetime.

Methodology to capture the single blade loads on a cross-flow tidal turbine flume model

The OPTIDE project aims to improve the efficiency and durability of Hydro-kinetic cross-flow tidal turbines (CFTT). These turbines are attractive for the exploitation of tidal energy, as the area-based power density of such turbine arrays is higher in comparison to those from horizontal-axis turbines. CFTT also generally feature a simpler design and the ability to operate under varying flow conditions. Nevertheless, the efficiency of single CFTT is lower relative to the most commonly used axial turbine type. Furthermore the life time can be affected by alternating and pulsating stresses, caused by continuous variations of the angle of attack and hydraulic loads during the rotation. These stresses may lead to structural damage and fatigue-induced material failures. A promising approach to overcome these drawbacks is intracycle blade pitching. In this case the angle of attack is continuously adjusted individually for each blade during the rotation. The consequence is smoothed peaks of the load alternations and a higher power coefficient CP . The project aims to explore the influence of active blade pitching on CFTTs and to optimize it with numerical and experimental means. Therefore, a lab-scaled three-bladed experimental turbine with embedded pitch actuators is developed. The model will subsequently be tested in the lab flume of the Institute of Fluid Dynamics and Thermodynamics of the Otto-von-Guericke University Magdeburg. Blade forces in tangential and radial components as well as the machine torque and the rotational speed are measured during the experiments. The turbine is equipped with two full-bridges of strain gauges for the detection of the blade loads, from which the structural stress is calculated subsequently. To ensure the turbine model’s mechanical durability, weakly coupled fluid-solid-interaction (FSI) simulations have been performed and will be presented. To this purpose, a 2D flow analysis, employing the open-source CFD toolkit OpenFOAM (v2206), has been coupled with a 3D structural analysis, using the Mechanical module of the commercial software package Ansys Workbench (2020 R2). The FSI simulations show that the current setup only allows for the measurement of the radial blade load component, because the pitching moment at blade level interferes with the measurements as soon as the profile stalls. The measurements are further distorted by secondary force paths from the loads on the other rotor blades. Possible measures for an improved instrumentation strategy on the flume model will be presented and discussed. It is shown that multiple equipment options allow for a decent investigation of the forces on blade level.

Synthetic eddy generation and modelling of turbine operation in a turbulent tidal flow

In the operation of hydrokinetic turbines in tidal sites, the effect of onset flow turbulence on device performance and reliability deserves particular attention. Computational Fluid Dynamics (CFD) models capable to describe this complex phenomenology are necessary to predict harmful operating conditions and to implement design strategies to mitigate the impacts. Similarly, the description of the interaction between turbine wakes and eddies in the onset turbulent flow is important in the study of tidal arrays.
 An original CFD methodology to simulate the operation of a tidal turbine in an arbitrary turbulent flow is presented. The methodology falls within the class of Synthetic Methods (SM). A randomly fluctuating velocity field is generated by a volume force distribution acting as forcing term in the Navier-Stokes equations. With respect to existing volume-force SM, an original definition of the forcing terms, and a control strategy to enforce a prescribed turbulence metrics are proposed. Volume force terms are imposed in a thin layer in the upstream region of the computational domain by a sinusoidal distribution with random variation of both intensity and phase. A Proportional-Integral-Derivative (PID) control is applied to minimize the difference between the intensity of the generated flow turbulence and the prescribed conditions.
 In [1] the model was applied to describe a turbulent stream in an unbounded flow by Detached Eddy Simulation (DES). The capability to generate eddies that evolve into a homogeneous, isotropic turbulent flow was demonstrated. Here, the model is applied to analyze the interaction between the generated onset turbulent flow and a tidal turbine. A computationally efficient approach is used here in which the turbine is described by a volume force method, in a similar fashion as turbulence generation is modelled. Specifically, a hybrid viscous/inviscid methodology is applied in which the DES solver is strongly coupled with a Boundary Integral Equation Method (BIEM) solver. At each time step, the blade load distribution is calculated by a time-accurate BIEM solution and recasts as volume force terms that are plugged into the DES solution. Examples of BIEM validation studies are given in [2, 3, 4] and in the results of a recent blind-test benchmark to be presented at the EWTEC 2023 Conference [5].
 The numerical application described here deals with a 3-bladed horizontal-axis tidal turbine in a 16% intensity, isotropic turbulent onset flow. In the full paper, the overall methodology is described, and numerical results are presented and discussed. Particular attention is given to characterize the generated turbulent stream in terms of key metric quantities like turbulence intensity, Power Spectral Density (PSD), time and spatial scales, isotropy, Probability Density Function (PDF). The results are analyzed to discuss the capability of the methodology to render a physically-consistent description of the phenomenology governing turbine operation in a real tidal flow.
 
 Gregori, M. et al., Mar. Sci. Eng. 2022. (https://doi.org/10.3390/jmse10101332)
 Sarichloo, Z. et al., Marine Energy Journal, 2022. (https://doi.org/10.36688/imej.5.77-90)
 Dubbioso, G.A. et al., Proceedings of EWTEC 2019.
 Salvatore, F. et al., Mar. Sci. Eng. 2018, 6, 53. (https://doi.org/10.3390/jmse6020053)
 Willden, R. et al., Submitted to EWTEC 2023.

Design, Manufacture and Testing of an Open-Source Benchmark Composite Hydrokinetic Turbine Blade

In a trend towards clean energy alternatives, recent years have seen great strides in the marine energy space. This has resulted in a pressing need for the design, development, and validation of novel energy harvesting technologies such as hydrokinetic devices, which capture kinetic energy from waves, tides, and currents. However, these devices span numerous concepts and designs that often lack solid benchmark research that can be freely referenced. This work focuses on the design process of an open-source composite hydrokinetic turbine blade for a three-bladed marine turbine rotor assembly with a diameter of 2.5 m. The proposed blade consists of two structural composite skins that are bonded with an adhesive and filled with a foam core. This study will explore and contrast the efficiency and resolution of low-fidelity rapid design methodologies and comprehensive high-fidelity approaches for the blade design, modeling, and analysis efforts, a key objective in this research. Blade hydrodynamic loads were modeled and applied to finite-element blade models to study deformations and potential failure. Ongoing efforts will result in blade manufacture and structural testing at the National Renewable Energy Laboratory. In future work, multiple blades will be deployed at the Living Bridge site at the University of New Hampshire and will be compared to rigid aluminum blades of the same geometry, developed by Sandia National Laboratories. Ultimately, this research will lay foundational groundwork for researchers and manufacturers, establishing a baseline composite blade design that will serve as a benchmark in the development of future hydrokinetic turbine blades.

A novel experimental method of power smoothing using supercapacitors and hydrogen for hybrid system PV/HKT

Nowadays, the intermittent nature of renewable energy systems represents one of the most significant challenges in isolated systems, where power fluctuations can cause instability and compromise energy quality. Although hydrogen systems and supercapacitors have been widely studied in the literature, they have been less investigated as participating agents, and further research is needed in this area. This paper presents a novel power smoothing method for an off-grid system that consist of photovoltaic panels, hydrokinetic turbines, fuel cells and a hybrid storage system (hydrogen and supercapacitors). Two well-known power smoothing methods were used to generate the power signals for the new method. The main novelty is based on controlling the state of charge of the supercapacitor using the fuel cell, for the reduction of power fluctuations and efficiently hydrogen produce. First, the capacity of the renewable system is optimized using the HOMER Pro software. Then, the optimized system was used to simulate the new method proposed in Matlab-Simulink. Finally, to validate the results obtained, extensive experiments were conducted in a laboratory test bench. The results showed that the power fluctuations index was reduced by up to 50 % in the electrolyzer and 20 % in the fuel cell, with a levelized cost of electricity of 0.19 USD/kWh. Therefore, the application of the new proposed energy smoothing method significantly improves hydrogen production.