Tidal Turbine Performance Research Articles

Multi-Objective Optimization Design of Dynamic Performance of Hydrofoil with Gurney Flap

The horizontal axis tidal turbine, as a crucial device for capturing tidal energy, has gained significant attention because it has better energy efficiency performance. Enhancing the performance of foils, a vital part of tidal turbine blades, can significantly improve tidal turbine performance. Among numerous methods to enhance the foil performance, the Gurney flap has gained significant attention due to its avoidance of complex structural design. Currently, there is limited research on optimizing the design of Gurney flaps while considering the dynamic performance of foils. In this study, the S809 foil with a blade cross-section was selected as the research subject, a multi-objective optimization design platform was created by integrating a multi-objective optimization algorithm with Computational Fluid Dy-namics (CFD) numerical simulation techniques. The objective of this platform is to enhance the dynamic performance of the hydrofoil by optimizing the geometric structure of the Gurney flap. The improvement of dynamic lift and the size of the dynamic stall hysteresis loop are used as objective variables in this study to evaluate the hydrofoil’s dynamic performance. The optimal Latin hypercube design method is used in the optimization process to choose sample locations, and the Kriging approximation model is used to determine the relationship between the design variables and the objective variables. Meanwhile, the Non-Dominated Sorting Genetic Algorithm-II (NSGA-II) is used to create a multi-objective optimization platform for solving the optimization problem, and the optimized results are validated using CFD. Comparative validation results show that quantifying the dynamic performance during hydrofoil pitching oscillation and using the optimal Latin hypercube design method and Kriging approximation model for optimizing the Gurney flap structure is rational and accurate. This study explores the mechanism of the Gurney flap through in-depth CFD numerical simulations and finds that the Gurney flap affects the flow characteristics at the hydrofoil’s trailing edge, thereby influencing the performance. It increases the pressure difference between the pressure and suction surfaces, thus enhancing the hydrofoil’s lift. Finally, this article provides three recommended parameters to improve the dynamic performance of the hydrofoil. This research can serve as a reference for the application of Gurney flaps in tidal turbine blade design.

Tidal turbine blade design optimization based on coupled deep learning and blade element momentum theory

The practical design optimization of blade structures is crucial for enhancing the power capture capability of tidal turbines. However, the significant computational costs required for directly optimizing turbine blades through numerical simulations limit the practical application of blade structure optimization. This paper proposes a framework for tidal turbine blade design optimization based on deep learning (DL) and blade element momentum (BEM). This framework employs control points to parameterize the three-dimensional geometric shape of the blades, uses convolutional neural networks to predict the hydrodynamic performance of each hydrofoil section, and couples BEM to forecast the performance of tidal turbine blades. The multi-objective non-dominated sorting genetic algorithm II is employed to optimize the geometric parameters of turbine blades to maximize the power coefficient and minimize the thrust coefficient, aiming to obtain the optimal trade-off solution. The results indicate that the prediction of the DL-BEM model agrees well with experimental data, significantly improving optimization efficiency. The optimized tidal turbine blades exhibit excellent power coefficients and reduced thrust coefficients, achieving a more balanced structural solution. The proposed optimization framework based on DL accurately and rapidly predicts the performance of tidal turbines, facilitating the design optimization of high-performance tidal turbine blades.

A deep learning approach for hydrofoil optimization of tidal turbines

Hydrofoil optimization plays a crucial role in improving the hydrodynamic performance of tidal turbines. However, the high-dimensional representations in hydrofoil design space require significant Computational Fluid Dynamics (CFD) simulations, increasing computational load and time expenditure. This paper proposes a hydrofoil optimization framework based on deep learning to achieve an effective mapping between design parameters, pressure fields, and hydrodynamic characteristics. The designed hydrofoil represented using the Signed Distance Function (SDF) is input to Convolutional Neural Networks (CNN) for fast prediction of hydrodynamic coefficients and pressure field. Due to the effective integration of the prediction model and genetic optimization algorithm, this framework can generate a large number of smooth hydrofoils and rapidly predict their hydrodynamic performance to achieve efficient optimization of hydrofoils. The optimized hydrofoil shapes obtained based on the above framework exhibit a higher lift-to-drag ratio than common hydrofoils. Furthermore, the optimized hydrofoils are applied to design tidal energy turbine blades. The simulation results demonstrate that the hydrodynamic performance of tidal turbines can be effectively improved through hydrofoil design optimization. The proposed framework enhances the design efficiency of the tidal turbine rotor and provides turbine hydrofoils with higher power coefficients.

Study on the performance of a floating horizontal-axis tidal turbine with pitch motion under wave–current interaction

Waves can induce motion in the floating platforms that support tidal turbines, affecting their hydrodynamic loads. To study the non-constant hydrodynamic of floating tidal turbines in a wave condition, this paper investigates the effect of pitch motion on the power coefficient (CP), thrust coefficient (CT), and wake flow of a tidal turbine using computational fluid dynamics. A pitch motion experiment is designed to verify the validity of the numerical method. The results show that the CP and CT exhibit periodic fluctuations under pitch motion, with the fluctuation period being consistent with the pitch period. Waves do not change the overall fluctuation trend of the CP and CT, but they do complicate the fluctuations and increase the likelihood of blade fatigue damage. Pitch motion reduces the mean power, with large-amplitude pitch motions particularly likely to result in severe power loss. The low-velocity region of the wake under pitch motion exhibits significant periodic oscillations. The wake is more susceptible to the pitch period than the pitch amplitude, and small-period pitch motions force the wake to deform earlier, accelerating wake vortex dissipation and velocity recovery. Increasing the immersion depth reduces the effect of waves on tidal turbine performance, but is not conducive to wake recovery. In summary, the rational design of the immersion depth and limiting the movement amplitude of the floating platform have the potential to prolong the working life of tidal turbines and increase their power output.

Effect of Wavelength on Turbine Performances and Vortical Wake Flows for Various Submersion Depths

When tidal turbines are deployed in water areas with significant waves, assessing the surface wave effects becomes imperative. Understanding the dynamic impact of wave–current conditions on the fluid dynamic performance of tidal turbines is crucial. This paper aims to establish a fundamental understanding of the influence of surface waves on tidal turbines. OpenFOAM, an open-source computational fluid dynamics (CFD) library platform, is utilized to predict the performance of current turbine under waves and currents. This research investigates the effects of two critical wave parameters, wave height and wavelength, on the fluid dynamics and wake structures of current turbine. Additionally, this study explores the influence of various submersion depths on turbine performance. The findings indicate that, under various wave conditions, the turbine’s average power coefficient remains constant, but significant fluctuations are shown. Increasing submersion depth can mitigate the impact of waves. However, in regions characterized by longer wavelengths, altering the submersion depth has limited effects on turbine performance.

The Advantages and Challenges of Carbon Fiber Reinforced Polymers for Tidal Current Turbine Systems - An Overview

A significant step in reducing the effects of greenhouse gases is obtaining electric energy from renewable sources. Electricity from tidal currents using underwater turbines is one of the most promising and well-liked technologies. The turbine systems are the key element in the tidal current energy. They are built using hydrodynamic principles to extract the most power possible from tidal ocean currents and are designed to last for extended periods in a maritime environment. The performance of tidal turbines is also significantly influenced by their materials, i.e., carbon fiber reinforced polymers (CFRP) used in them. This paper also reviews the CFRP materials used in tidal current turbine systems. Besides, an analysis of their advantages and challenges regarding CFRP materials that can impact tidal current turbine efficiency is further explored.

Hydrodynamic Performance and Flow Field Characteristics of Tidal Current Energy Turbine with and without Winglets

In order to gain a more comprehensive understanding of the influence of winglets on the hydrodynamic performance and flow field characteristics of tidal current energy turbines, two different shapes of winglets are designed, and numerical simulation results for turbines with and without winglets are compared and analyzed. The results show that both shapes of winglets can improve the energy conversion efficiency, and the winglets with a cant angle (60°) are more effective than the flat (0°) winglets; the winglets transfer the tip vortices to the winglet tips and weaken the tip vortices, increase the pressure coefficients of the cross-section in the tip region, and inhibit the three-dimensional flow phenomenon in the tip region; the winglets will make the wake axial velocity deficit larger in the near-wake region, and with the axial distance increases, the axial velocity of the wake flow with winglets recovers faster than that without winglets; winglets can make the vortex pairing and breaking of the turbine tip vortex faster, which can also be observed by the change in the turbulent kinetic energy (TKE).

Numerical Study of Ducted Turbines in Shallow Water Environment

The development of tidal turbines, particularly for shallow water applications, is still in its early stages. Vertical axis tidal turbines (VATT) are often preferred for shallow water due to the bidirectional nature of tidal currents. Implementing a channelling system around a tidal turbine can significantly stabilise the flow field, increase the current velocity, and enhance the energy efficiency of the turbine. However, there has been limited exploration of using channelling techniques to improve the performance of VATTs in turbid areas. This study employs a numerical analysis using computational fluid dynamics (CFD) to investigate VATTs. The VATT model is represented by a cylindrical object with a diameter and height of 5 meters. The simulation focuses on the wake characteristics and the design of turbine arrays. The Reynolds-Averaged Navier-Stokes (RANS) equations are utilised as flow viscous solvers in ANSYS Fluent, and the effectiveness of the ducts in energy conversion is calculated using the realizable two-layer turbulence model. The primary objective of this study is to examine the impact of converging devices on tidal turbine performance and propose an optimal design for shallow water applications. The proposed ducted design shows an increase in current speed passing through the device by 11.1%. Although the wake generated by the multi-row staggered array layout disperses the flow to the side of the domain, the model demonstrates a 0.9% improvement in velocity magnitude. Conversely, the results for the single-row inline layout indicate the most favorable arrangement for shallow water applications, with a 19.4% increase in velocity magnitude and a shorter wake generation.

A Numerical study on the effect of solidity on the performance of Transverse Axis Crossflow Tidal Turbines

This paper presents a three-dimensional numerical study employing an actuator line model to investigate the effect of turbine solidity on the performance of a Transverse Axis Crossflow Turbine (TACTs). Transverse Axis Crossflow Turbines have a low rectangular form and are ideally suited to relatively shallow tidal and riverine sites due to their ability to handle bi-directional flow intake. Lift based TACTs are not well understood due to their complex hydrodynamics when the downstream sweep passes through the wake produced by the turbine shaft and the upstream sweep. The blade loading, hydrodynamics and ultimately power produced during the downstream sweep depends on the number of blades and turbine solidity. This numerical study is carried out using OpenFOAM and replicates planned fieldwork where the power and in-service blade loading will be monitored as a function of turbine solidity. Turbine solidity is a dimensionless parameter that measures the proportion of blade area to the projected turbine frontal area. Turbines achieve peak performance at an optimum solidity and tip speed ratio. Solidity can be varied by changing the number of blades or changing the turbine radius. An increase in solidity causes the peak performance to reduce and shift to a lower tip speed ratio albeit with a greater torque.
 This paper also explores the effect that maintaining turbine solidity has on turbine performance over a range of typical inflow velocities. Turbine solidity is held constant by varying both the number of blades and turbine diameter. Iso-solidity has been investigated for horizontal axis wind turbines but little is known about the effect of maintaining turbine solidity on TACT performance.

Influence of the number of front and rear rotor blades on the hydrodynamic performance of counter-rotating horizontal-axis tidal turbines

The coaxial rotor structure presents significant potential for the development of tidal turbines. In order to study the effect of the number of front and rear rotor blades on the hydrodynamic performance of counter-rotating horizontal-axis tidal turbines (CRHATTs), three models (CRHATT 3-2, CRHATT 3-3 and CRHATT 3–4) are established at the same tip speed ratio (TSR), and the accuracy of the numerical method is verified by experiments. The effect of blade number on the performance coefficients, velocity and pressure pulsations and vortex structure of CRHATTs are calculated based on CFD method and spectral analysis. The results show that the relationship of the power coefficient for the three models is: CRHATT 3–4 > CRHATT 3-3 > CRHATT 3-2. The turbulent kinetic energy in the flow field can be transferred more quickly from the large-scale vortex structure to the small-scale as the number of rear rotor blades increases. By weighing aspects such as load fluctuation and power coefficient, the CRHATT 3–4 can produce the largest power coefficients, the best stability during operation and the least vibration on the blades among the three models. This paper provides significant guidance for the engineering design and optimization research of CRHATTs.

Influence of the spatial variation of upstream velocity on a vertical-axis tidal turbine performance

Assessment of the upstream flow available to the tidal energy converters (TEC) is key to evaluate its performance. Simultaneously, TEC technology has been innovating on its concepts and designs to expand the potential sites to harvest energy generated by tidal currents and rivers. The Gkinetic CEFA 12 is an easy-to-deploy device suitable to operate on estuary environments. The design consists of two 1.2 m vertical axis turbines attached to the sides of a buoyant platform, which uses a bluff body to accelerate the incoming flow to the rotors. The device was deployed on a single point mooring enabling passive flow alignment. As part of the Vertical axis tidal turbines in Strangford lough project (VATTS), the upstream flow has been measured using acoustic doppler profilers (ADP) mounted on the TEC during its operation in Strangford lough. Recommendations of IEC-200 were followed when mounting the ADPs relative to Gkinetic. However, the continuous repositioning of the TEC according to the prevailing tidal regime affects the ADPs heading. The implications of the spatial variation of the rotor’s upstream velocity on the resource assessment and device performance are not clear since this situation is not typical.To investigate the spatial variation of the upstream velocity two ADCP deployment locations were made. A seabed (upward facing) ADCP as per the current standards and a device mounted (downward facing) ADCP upstream of the rotor plane. Evaluation of the influence of the following three factors were made: i) the ADPs direction repositioning according to prevailing tidal regime, ii) the proximity of the sensors to the sea-surface, and iii) the proximity of the sensors to the TEC.These three factors will be evaluated using ADP datasets collected at Strangford narrows during the VATTS project. The datasets were obtained at approximately the same location of the TEC operation. They enable the study of the following scenarios 1) incoming flow to the rotors during operation, 2) incoming flow on undisturbed conditions (no turbine operation), and 3) a harmonic analysis prediction of the undisturbed incoming flow, which solely captures the tidal-driven flow.The investigation of these three scenarios will provide a better understanding on the rotor’s upstream flow spatial variation, and the influence of the device’s proximity and near sea surface conditions on the mean flow. These findings would benefit developers of alternative TEC designs that operate near the sea-surface.

Designing Vortex Generators for Tidal Turbine Blades

Increasing tidal turbine performance through innovation is crucial if the cost of tidal energy is to become competitive compared to other sources of energy. The present investigation deals with the application of Vortex Generators (VGs) on tidal turbines in view of increasing their performance. The more mature wind energy industry uses passive VGs either as a retrofit or in the blade design process to reduce separation at the inboard part of wind turbine blades. Tidal turbine blades also experience flow separation and here we examine whether passive vane VGs can be used to reduce or suppress that separated flow.
 Vortex generators (VGs) in various forms have been used and studied for flow separation control on wings since the 1940s [1]. Their working principle is relatively simple: they generate streamwise vortices that energise the boundary layer on the surface they are attached to, by bringing high momentum fluid closer to the surface [2]. This mechanism has been described by various researchers [3–6], while a number of studies have provided optimization guidelines under a variety of flow conditions [7–13].
 In the present investigation, a VG configuration is selected following a thorough wind tunnel campaign. It is found that sizing parameters for the tidal turbine profile are very similar to the wind turbine relevant literature [13,14]. The best performing vane VG configuration had a height of 0.007c, which corresponded to half the local boundary layer height (0.5δ) for operational Reynolds numbers. The results are also used to validate a Reynolds Averaged Navier Stokes (RANS) VG modelling approach using the BAY model [15]. The validated method is used to simulate the flow past a tidal turbine in both model size (1:8) and full scale, see Figure 1. The results show that VGs do suppress flow separation in both cases. However, and importantly, it is revealed that the significance of rotational effects is such that when deciding VG placement locations, only the full size blade should be considered. In the interest of brevity, the performance increase caused by a standard VG configuration is show in Figure 2, where a power coefficient improvement of 1.05% is predicted at λ=3. Figure 3 shows the effect on the normal and tangential forces on the blade. In the final paper and presentation, the results for different VG locations will be included and analysed in detail.

Viability Analysis of Tidal Turbine Installation Using Fuzzy Logic: Case Study and Design Considerations

Tidal energy represents a clean and sustainable source of energy generation that can address renewable energy challenges, especially the global challenge of optimizing alternatives for stable supply. Although tidal stream energy extraction technology is in the early stages of development, it shows great potential compared to other renewable energy sources. The main objective of this research is to provide a digital tool for the optimization of the installation of turbines through fuzzy logic. The methodology in this study includes the design and development of a fuzzy-logic-based tool for this purpose. Design criteria included parameters such as salinity, temperature, currents, depth, and water viscosity, which affect the performance of tidal turbines. These parameters are obtained from the geographic location of the installation. A decision-making system is provided to support the tool. The designed fuzzy logic system evaluates the suitability of different turbine locations and presents the results through graphics and probability of success percentages. The results indicate that currents and temperatures are the most limiting factors in terms of potential turbine locations. The program provides a practical and efficient tool for optimizing the selection of tidal turbines and generating energy from ocean currents. This tool is evaluated and validated through different cases. With this approach, the aim is to encourage the development of tidal energy and its adoption worldwide.

Effects of Slotted Blades on the Hydrodynamic Performance of Horizontal Axis Tidal Turbines

The horizontal axis tidal turbine (HATT) is a device that harnesses the energy of ocean currents and converts it into electrical energy. The blade plays a crucial role in the efficiency of power generation in HATTs. This study focuses on the use of slotted blades to enhance the efficiency of HATTs and investigates the flow control mechanism of these slots using computational fluid dynamics (CFD) methods. Initially, CFD simulations were conducted to analyze the impact of the slot’s geometry parameters on a two-dimensional (2-D) slot and to demonstrate its passive fluid control mechanism. Subsequently, the slot was implemented on three-dimensional (3-D) blades to examine its effect on the hydrodynamic performance of the blades. The results of the 2-D simulation indicate that the width and position of the slots have a significant influence on the lift-to-drag ratio of the hydrofoils, resulting in a maximum increase of 166%. For the 3-D blades, the simulation results reveal that the slot can enhance the power coefficient of the blades, particularly at low tip-speed ratios, with a maximum increase of 7.8%.

Experimental and Computational Fluid Dynamic Study of Water Flow and Submerged Depth Effects on a Tidal Turbine Performance

This study involves an experimental and numerical analysis of the Hunter turbine, a vertical axis turbine utilized for tidal energy. A laboratory model of the Hunter turbine, featuring an aspect ratio of 1.2, was designed and tested. Numerical equations, including the Reynolds-averaged Navier–Stokes (RANS) constant, were analyzed through computational fluid dynamics (CFD) software using the k-ω turbulence model to forecast turbine performance and other related flow specifications, such as pressure lines, stream velocity, and pressure. This simulation was conducted on the surface of the turbine blade, and the results were obtained accordingly. The experimental data were utilized to verify the numerical results, and the difference between the two was reasonably acceptable. The turbine was studied in six different flow coefficients and four different vertical positions. The results indicated that the power coefficient increased as the submerged depth from a water-free surface increased, and after a specific depth, the output power remained constant. It was also observed that the minimum depth from a water-free surface for maximum power coefficient was three times the diameter of the turbine drum (3D).

Research on Wake Field Characteristics and Support Structure Interference of Horizontal Axis Tidal Stream Turbine

The harnessing and utilization of tidal current energy have emerged as prominent topics in scientific inquiry, due to their vast untapped resource potential, leading to numerous investigations into the efficacy of hydrokinetic turbines under various operational conditions. This paper delineates the wake field characteristics and performance of horizontal axis tidal stream turbines under the influence of support structures, using a comprehensively blade-resolved computational fluid dynamics (CFDs) model that employs Reynolds-averaged Navier–Stokes (RANS) equations in combination with the RNG k-ε turbulence model. To achieve this, the study utilized experimental tank tests and numerical simulations to investigate the distribution characteristics and recuperative principles of the turbine’s wake field. The velocity distribution and energy augmentation coefficient of the wake field showed strong agreement with the experimental results. To further assess the effect of support structures on the flow field downstream of the unit and its performance, the hydrodynamic attributes of the turbine wake field were analyzed with and without support structures. The interference elicited by the support structure modified the velocity distribution of the near-wake flow field, resulting in a 4.41% decrease in the turbine’s power coefficient (Cp), significantly impacting the turbine’s instantaneous performance.

Research on the effect of yawing motion on tidal turbine performance based on actuator-line method

An actuator line method (ALM) code is used to investigate the yaw motion of tidal stream turbines, using different induced frequencies, amplitudes and starting angles. The relative velocity in the ALM calculation is corrected by considering the reaction force of the water on the floating tidal turbine. Because the ALM directly converts the flow velocity characteristics on the mesh element into the force characteristics, more small-scale and high-frequency signals appear, compared to Blade-Resolved Method simulations. In the results, the oscillation frequency of power coefficient and thrust coefficient (Cp, Ct) is twice of the yawing motion frequency when the starting yaw angle is 0°. Increasing the yawing amplitude as well as the starting angle both lower the mean values of Cp and Ct whilst the effect of frequency is slight. The turbine's hydrodynamic coefficients are obtained by best-fit model. The yawing amplitude has a moderate effect on the constant hydrodynamic terms.

Using vortex generators for flow separation control on tidal turbine profiles and blades

Tidal energy can play an important role in the Net Zero transition. Increasing tidal turbine performance through innovation is crucial if the cost of tidal energy is to become competitive compared to other sources of energy. The present investigation is a proof-of-concept study for the application of Vortex Generators (VGs) on tidal turbines in view of increasing their performance. The more mature wind energy industry uses passive VGs either as a retrofit or in the blade design process to reduce separation at the inboard part of wind turbine blades. Tidal turbine blades also experience flow separation and here we examine whether passive vane VGs can be used to reduce or suppress that separated flow. First, a wind tunnel investigation is performed to assess the performance of VGs on a 20% thick profile from the blade. Then, the VG effect on the 2D-profile is modelled in a Reynolds Averaged Navier-Stokes in-house solver. Results show that low profile VGs, i.e. VGs shorter than the local boundary layer, can increase the performance of the blade profile and successfully reduce flow separation. The VG effect on blade performance is examined in model scale and in full-size. VGs successfully suppress separation in both cases and it is shown that full-size information should be used for the placement of VGs. A maximum power coefficient increase of 1.05% is observed at a tip speed ratio of λ=3. The present proof-of-concept study demonstrates for the first time the potential of passive VGs to be included either in the design process of a tidal turbine blade or as a retrofit solution.

An investigation of tidal turbine performance and loads under various turbulence conditions using Blade Element Momentum theory and high-frequency field data acquired in two prospective tidal energy sites in Australia

Potential tidal energy sites are characterized by strong currents and high levels of shear, which is the main source of turbulent kinetic energy production. Enhanced turbulence levels are known to intensify fatigue loads acting on turbine blades, possibly causing premature device failure. Blade Element Momentum (BEM) numerical models allow for the investigation of device performance and loadings prior to device deployment and support turbine design optimization at low computational expenses. High-frequency novel Acoustic Doppler Current Profiler (AD2CP) data from two tidally energetic sites in Australia are used to feed a BEM model optimized to incorporate unsteady flow corrections. Power, thrust and bending moments coefficients as well as separation points are estimated to describe the performance of a turbine under various turbulence intensities and integral length scales. Results reveal that standard deviations were more sensitive than mean coefficients and turbulence intensities had a greater impact on performance coefficients than integral length scales. Periodic oscillations of separation points at two stations suggest the presence of weak dynamic stall but also that leading-edge vortex shedding is constrained to the blade roots. These findings highlight the need of assessing turbulence in tidal energy sites and support design improvements which can endure unsteady conditions.

Tidal turbine performance and loads for various hub heights and wave conditions using high-frequency field measurements and Blade Element Momentum theory

Understanding the impacts of unsteady flows on tidal turbine performance and loadings prior to device deployment is essential for mitigating the effects of large hydrodynamic forces and avoiding premature fatigue. High-frequency velocity measurements from an energetic tidal channel were fed into a model that couples Blade Element Momentum (BEM) theory with dynamic stall and rotational augmentation corrections. A model turbine operating in real-world conditions was used to investigate different hub submergence depths and also extreme wave conditions. Mean turbine coefficients were more affected by varying levels of shear than by waves while standard deviations were more sensitive to shear than to the proximity of surface waves. Under long waves, power and thrust coefficients reached more than twice the average values and standard deviations are enhanced by over 70%. Waves moved the separation point towards the leading edge in over half the blade span and thus impacting the stall behaviour. These outcomes contribute to the understanding of power extraction and hydrodynamic forces around turbine blades in real-world conditions. This analysis is important for turbine developers to design resistant structures and thus extend device durability, but also to improve turbine performance.