Average Power Coefficient Research Articles

Aerodynamic performance improvement of Savonius wind turbine through a passive flow control method using grooved surfaces on a deflector

A Savonius rotor is a Vertical-Axis Wind Turbine (VAWT) that converts wind force into torque on a rotating shaft. The poor efficiency of this rotor is caused by the unfavorable negative torques generated as the returning blade rotates against the incoming flow. The current study aims to improve the aerodynamic performance of a Savonius wind rotor by installing a cylinder deflector with different grooved surfaces as a unique deflector system to offset the negative impact at the wake zone downstream of the deflector. The grooved surface is essentially one way to alter the surface roughness of a cylinder, which has shown to be quite successful to control vortex shedding and wake formation behind the cylinder. In contrast to previous research, a grooved surface of a cylinder deflector was used instead of traditional deflectors to increase the aerodynamic performance by disrupting the wake zone downstream of the deflector. With this motivation, a systematic parametric study via Computational Fluid Dynamics (CFD) method was implemented for different combinations of the flow and geometric characteristics including Tip Speed Ratio (TSR) value, groove shapes (rectangular, U, and V), groove number, and size. Besides, the flow over a smooth cylinder was analyzed and compared with that of grooved cases to determine the ideal groove configurations for enhancing the total output power. The results demonstrated that the optimal deflector with the U-grooved surface augmented the aerodynamic performance the most for all TSRs. The optimal deflector has 12 U-grooved surfaces with a diameter size of 0.025 of rotor diameter. The average power coefficient enhanced dramatically up to 24.2% and 15.8% through the deflector with a U-grooved surface at TSR = 0.9 in comparison to without deflector case and smooth cylinder deflector case, respectively.

Misaligned sheared flow effects on a ducted twin vertical axis tidal turbine

Most tidal turbines experimental tests are carried out in idealised conditions with uniform velocity profiles and without flow misalignment. However, at sea, the velocity profiles are mostly sheared and the flow direction spreads out around the main direction. In this study, we address experimentally the effect of those realistic conditions on the response of a twin counter-rotating vertical axis tidal turbine in Ifremer’s wave and current flume tank. At the whole turbine scale, the current shear hardly affects the drag and the average power coefficient but it leads to a 35 % increase of the power standard deviation. The flow misalignment does not affect the power production but it raises the average drag coefficient by 15 % for a ±15°angle of incidence. At the rotor column scale, both the shear and the misalignment modify the torque distribution with regard to the blades angular position, with a torque asymmetry up to 30 % between the upper and lower rotors, among other effects. Absolute rotor angular position as well as blades local flow visualisation would be needed to explain the complex torque distribution on a rotor column, which must be taken into account in the turbine design. This paper also provides a wide experimental database for the validation of numerical models applied to ducted twin vertical axis tidal turbines.

Experimental performance and wake study of a ducted twin vertical axis turbine in ebb and flood tide currents at a 1/20th scale

While studies on horizontal axis tidal turbines are plentiful, those on ducted twin vertical axis alike HydroQuest’s turbines are lacking. For such a device, both the relative counter-rotation direction of the rotors and the tripod base geometry upstream are different between ebb and flood tide. Consequently, this paper analyses the effect of the two opposed flow directions on the hydrodynamic performance and on the wake of the turbine. The study is based on experimental measurements at a 1/20th scale in Ifremer’s wave and current flume tank. The hydrodynamic performance of the model are characterised over a wide range of operating points with the turbine installed on a tripod and on a monopile base. In addition, the 3D wake of the turbine is thoroughly analysed in the two flow directions using 3-component laser Doppler velocimetry. Overall, the drag and the maximum average power coefficient are not affected by the current direction but the optimal tip speed ratio is 7 % lower during ebb with 1.5 times higher power fluctuations compared to flood tide. Besides, the wake of the two rotor columns interact differently depending on the flow direction, leading to a 30 % faster surface averaged velocity recovery in the flood tide configuration. The observed effect of flow direction provides a better knowledge of twin vertical axis turbine wake interactions and highlights the impact of the gravity base geometry on the development of the overall turbine wake. This paper also provides a wide experimental database for the validation of numerical models applied to ducted twin-vertical axis tidal turbines.

Evolutionary optimization of a Savonius rotor with sandeel-inspired blades

A possible way to capture the kinetic energy available in the wind and then convert it into a useful form of energy is to use wind turbines. Out of many kinds of wind turbines, a lot of in-depth studies have been conducted to improve the performance of the drag-based vertical-axis wind turbine called Savonius rotor. This kind of vertical-axis wind turbine usually suffers from poor energy conversion efficiency, particularly for its conventional shape (thin half-cylinders). In the current work, a bionic blade shape of the Savonius-type wind turbine rotor inspired by sandeels (also called sandlances) is proposed, combined with an optimization step in order to maximize performance. Sandeels are slim elongated fish that often swim in vast shoals. The bionic blade is described by two principal geometrical parameters, both divided by the blade length (d); the maximum blade camber (fmax) and its location (Xfmax). The optimization relies on evolutionary algorithms to maximize the average power coefficient of the Savonius rotor with sandeel-inspired blades when varying the two design parameters. A total of 128 individuals have been evaluated numerically using a series of two-dimensional transient simulations with the software Star-CCM+. In comparison to the conventional rotor with two arc-type semi-circular blades, the optimal design with sandeel-inspired blades exhibits a considerable increase in turbine efficiency of up to 9.21% at the design tip speed ratio (λ = 0.8). Investigating the performance over the entire operating range results in a maximum power coefficient of 0.255 by the optimal rotor, leading to a gain of about 10.58% with respect to the standard rotor at λ=1.

Fast prediction of hydrodynamic load of floating horizontal axis tidal turbine with variable speed control under surging motion with free surface

For floating HATT11HATT: horizontal axis tidal turbine with variable speed control, a numerical model based on CFD22CFD: Computational fluid dynamics method is proposed to predict the surge force. Compared with the hydrodynamic load of the HATT under the same condition but with fixed speed control, the variable speed control can effectively improve the power coefficient of the HATT. When the surge period is 1.5 s and the surge amplitude is D/8, the average power coefficient increases by 36.36%. But the load fluctuation in terms of the axial load and power coefficients are significantly larger than those with fixed speed control. Based on the hydrodynamic load decomposition model of the HATT with fixed speed rotation and surging motion and the variation law of damping coefficient, the hydrodynamic load prediction method of the HATT with variable speed rotation and surging motion is established. By comparing with the CFD results, it is evidenced that this prediction method can effectively predict the axial load and power coefficients of the HATT. The research findings can provide a reference for the rapid prediction of the hydrodynamic load of the HATT during the actual operation of the floating tidal power station.

Effects of unsteady stream on hydrodynamic behavior of flexible hydrofoil in semi-passive mode

The effects of unsteady stream on the hydrodynamic behavior of a flexible hydrofoil in the semi-passive mode are investigated in this study with the goal of improving power extraction. Specifically, the influences of flow velocity amplitude (λ), the frequency ratio (σ) between hydrofoil and flow velocity, and phase difference (ε) between the flow velocity and pitching motion of the hydrofoil are examined. The results reveal that σ has a significant effect on lift force and heaving velocity, thus severely affecting the average power coefficient (CP‾) and heaving response. The peak value of CP‾ is attained when σ = 2; this is attributed to the satisfactory synchronization between the flow velocity and heaving motion of the hydrofoil. Initially, CP‾ increases with ε until ε = 90°; then, it decreases as ε further increases. The equilibrium position of the heaving response is sensitive to both ε and λ. The relative relationship between the flow velocity and pitching motion is modified by ε, altering the evolution of the lift force, heaving velocity, vortex, and pressure distribution. Through comprehensive adjusting σ and ε according to λ, the hydrofoil encounters minimum incoming flow near the dead point. This is the key to improve power extraction.

Insights into the flow dynamics and rotor performance of a Savonius turbine with dynamic venting using controllable flaps

The drag-driven vertical-axis turbines with semicircular rotor blades, commonly known as Savonius turbines, remain potentially beneficial to extract renewable energy from wind and water streams, especially in terms of their practicality to provide low-cost solutions to rural areas. However, they suffer drawbacks due to the negative torques on their returning blades. We propose a novel solution by dynamically venting out these returning blades using controllable flaps, which retained their omnidirectional capability. Results from unsteady numerical simulations showed that the vented rotor attained a maximum average power coefficient (CP) of 0.275 at the tip-speed ratio (symbolized as λ) of 0.9, which was 21.7% better than that on the unvented rotor. Furthermore, the proposed dynamically vented blades produced large improvements in the average torque coefficient (CT), with maximum gains of 38.3% on the returning blade at λ = 0.4 and 24.8% on the full rotor at λ = 1.0, relative to those on the unvented rotor. The controlled dynamic venting was beneficial because it modified the pressure distributions surrounding the returning blade and changed the flow structure downstream of the vented blade that improved the torque on the subsequent blade entering the returning side. Elucidation on the flow dynamics revealed that the flows were vented outward through the flap aperture onto the convex side of the returning blade, rather than inward into its concave side, as initially hypothesized.

Effect of micro-cylinder as a passive controller on the Darrieus wind turbine performance

Vertical Axis Wind Turbines are more suitable for urban areas than Horizontal Axis Wind Turbines because they operate at lower wind speeds, and produce less noise, and are less expensive. In this study, the Darrieus turbine (three blades) is chosen as one of the (VAWTs) based on the NACA 0018 airfoil. The aerodynamic analyses are carried out by ANSYS Fluent software based on finite volumes method and the unsteady Reynolds averaged Navier–Stokes (URANS) equations with Shear Stress Transport (k-ω SST) turbulence model. The target of this work is to improve the performance of the Darrieus turbine by installing a micro-cylinder in various positions and various diameters. Three different micro-cylinder diameters are examined with a ratio of the micro-cylinder diameter to the chord (d/c = 0.029, 0.05, 0.065). It has been observed, the micro-cylinder improves the turbine performance in two cases: (1) The micro-cylinder diameter is smaller where the average power coefficient (CP-avg) increased by 9.5% compared to the conventional turbine at MC1 (d/c = 0.029). (2) By installing the micro-cylinder on the front of the blade leading edge where the average power coefficient (CP-avg) increased about 14.1% compared to the conventional turbine at the location (MC8). On the contrary, if the micro-cylinder diameter has lager diameter or located on the suction side or down towards the pressure side of the blade leading edge, the turbine performance decreases.

Investigation of the combined influence of arrangement and configuration parameters on the performance of vertical axis wind turbines in staggered arrangements

Vertical-axis wind turbine (VAWT) array has attracted much attention due to its higher power density, but existing studies put little emphasis on the configuration parameters of one VAWT in array. Thus, a comprehensive study was carried for the combination effect of arrangement and configuration parameters on the aerodynamic performance of two VAWTs in staggered arrangements. Mutual influence of two turbines under different relative arrangement angles (θ), turbine spacing, blade pitch angles (BPA), and tip speed ratios of the downstream turbine were investigated. A major finding is that the location of the downstream VAWT can be divided into two regions with θ = 60° as the turning point, where the regular patterns of the average power coefficient of double VAWTs (CP,avg) with BPA are different. When the downstream turbine is located in the high-speed zone (θ ≤ 60°), positive BPAs benefit the performance of turbines, and 2.5° is the general optimal BPA. While for the case of downstream VAWT in the wake region (θ > 60°), the optimal BPA is a variable related to turbine spacing. Compared with the zero pitch blade, the maximum CP,avg can increase by 7.3% at most (in the 2D-75° case). Flow characteristic analysis indicated that the trigger of the dynamic stall and the wake interaction is the main reasons for different operation features of staggered arrangements.

Numerical and experimental study on power extraction performance of a semi-active flapping airfoil with bioinspired dimple

Inspired from the special structure of dragonfly wings (cambered and corrugated groove), in this work, the bioinspired dimple structure is introduced into the design of the airfoil to improve the power extraction performance of a semi-active flapping airfoil, and the characteristic parameters of the bioinspired dimple structure are optimized by the combination of numerical analysis and Taguchi method. The results show that the bioinspired dimple can effectively improve the performance of the flapping airfoil. The average power coefficient and power extraction efficiency of the optimized dimple flapping airfoil are 31.73% and 31.23% higher than that of the baseline smooth airfoil respectively, and the influence of the three considered characteristic parameters on the power extraction performance is ranked as: lx (the location of bioinspired dimple) >ly (the depth of bioinspired dimple)>w (the inlet width of bioinspired dimple). Further analysis the flow field around the flapping airfoil shows that the bioinspired dimple can promote the separation of the leading edge vortex from the airfoil surface during stroke reversal, meanwhile at the process of upstroke and downstroke, the bioinspired dimple can also delay the leading edge vortex to separate, which is the reason for the dimple airfoil extract more power from the fluid. Based on the numerical results, experiments test are also carried out to evaluate the power extraction performance of the optimized bioinspired dimple airfoil, and the results show that at the same experiment condition, more 12.81% average power coefficient is extracted by the optimized dimple flapping airfoil, which again verifies the effectiveness of the numerical analysis conclusion obtained in this work.

Numerical Experiments on Hydrodynamic Performance and the Wake of a Self-Starting Vertical Axis Tidal Turbine Array

In this paper, based on the CFD software ANSYS-Fluent, two-dimensional numerical models are established to investigate the hydrodynamic performance of a self-starting H-Darrius vertical axis tidal turbine (VATT) array of three turbines in a triangular layout with 3D in axial and radial distance. Three main aspects are explored in this study: (1) the self-starting performance, power coefficient, flow fields, and blade force of the double-row VATT array, which are compared with a stand-alone turbine, (2) the wake development of the front and rear displacement turbines, and (3) the feasibility of the double-row self-starting VATT array in practical applications. It is found that the power coefficients of the three turbines in the array all improved compared with that of the stand-alone turbine, and as the load increased, the difference between the averaged power coefficient of the array and a stand-alone turbine was more obvious, with a maximum difference of 3%. The main effects of the front turbines on the rear turbine are energy utilization and turbine vibration. Due to the beam effect between the front turbines, the incident flow rate of the rear turbine increased to approximately 1.2 times the free flow rate. However, the greater rotational fluctuations of the rear turbine mean that although it had a higher power factor, it was more susceptible to fatigue damage. The wake of the rear turbine in the array had a much larger area of influence on both the length and width, but the velocity deficit recovered more quickly to over 95% at a distance of 10D behind it. The rate of wake velocity recovery is load-dependent for a stand-alone self-starting turbine, but this was not evident in the arrays. The positive torque of the turbine is mainly generated when the blade rotates through an azimuth angle from 45° to 160° and mainly benefits from the inner side of the blade. For the double-row three-turbine array, the axial and radial spacing of 3D is reasonable in practical applications.

Optimal design of Savonius wind turbine blade based on support vector regression surrogate model and modified flower pollination algorithm

Blade shape has a significant effect on the wind-capturing ability of the Savonius wind turbine. This paper proposes an intelligent optimization method for optimizing the shape of the blade of the Savonius wind turbine. This method firstly uses the cubic Bezier curve with four design parameters (x1, y1, x2, y2) to characterize the complex blade shape, and then uses the Latin hypercube sampling method to sample some design schemes throughout the design space, and uses computational fluid dynamics simulation to evaluate the response value, i.e. the moment coefficient, of each scheme, and then uses the support vector regression surrogate model to describe the relationship between the design parameters and their response values, finally uses modified flower pollination algorithm to solve the surrogate model to obtain the optimal blade shape. After comparing and analyzing the optimized blade and the classical semicircular blade, it is found that compared with the classical semicircular blade, the optimized blade has a better wind-capturing ability. When the wind speed is 7 m/s and the tip speed ratio is 1, its average power coefficient Cp is significantly increased from 0.260027 to 0.277902 (about 6.87% higher). In addition, the aerodynamic performance of the optimized blade is also better than the classical semicircular blade at other tip speed ratios (TSRs = 0.6–1.2). It is shown that the wind turbine with the optimized blade has great potential in a practical application environment.

Response Surface Optimisation of Vertical Axis Wind Turbine at low wind speeds

The Vertical Axis Wind Turbines (VAWTs) have an increasing global market and this emphasis the need for to improve the performance of VAWTs, especially at relatively low wind speed. This paper utilises the Response Surface methodology to optimise the performance of a VAWT. A three bladed VAWT configuration was considered with a NACA0015 profile. Three significant input parameters were selected including the tip speed ratio, the turbine solidity, and the pitch angle. An extended range of each input parameter was chosen in order to gain a good insight into how these input parameters affect the performance of the VAWT. The high-fidelity Computational Fluid Dynamics (CFD) simulations were carried out for the modelling of the turbine. The use of the Response Surface Optimisation based on Multi-Objective Genetic Algorithm (MOGA) along with the CFD simulations is found to be useful in the selection of the optimal design of VAWT. Moreover, the 3D aspects of the VAWT geometry are investigated and these include the turbine aspect ratio and the effect of the blade tip geometry. The implementation of an optimised winglet at the tip of the turbine blades is found to provide a significant enhancement of the cycle averaged power coefficient, especially at low aspect ratios.

Characterization of wake interference between two tandem offshore floating vertical-axis wind turbines: Effect of platform pitch motion

The wake interference within the offshore wind farms, especially with the tandem arrangement scenario, affects the designed total power output. Also, the six degrees of freedom motions of the platforms not only can change the aerodynamics of the offshore floating wind turbines, but also may influence the wake interference between them. In the present study, the effect of the platform pitch motion on the wake interference between two tandem offshore floating vertical-axis wind turbines (VAWTs) is characterized using the improved delayed detached-eddy simulation (IDDES). First, the power performance of the downstream turbine (VAWT Ⅱ) at different separation distances, 2D ≤ LS ≤ 10D, and tip speed ratios, 0.4 ≤ TSRⅡ ≤ 1.5, are analyzed, assuming that the upstream turbine (VAWT Ⅰ) is bottom-fixed and operates at an optimal TSRⅠ of 1.2. Then, the effects of the pitch amplitude, 5° ≤ APⅠ ≤ 15°, and pitch period, 2TⅠ ≤ TPⅠ ≤ 8TⅠ, on the wake interference are characterized by assuming that the platform pitch motion of VAWT Ⅰ follows a prescribed simple harmonic law. The results show that locating VAWT Ⅱ in the medium wake region of VAWT Ⅰ, e.g., LS = 6D, can appropriately balance the power performance and space cost of the bottom-fixed turbine array. Also, the platform pitch motion can reduce the mean velocity deficit in the core wake region of VAWT Ⅰ. The mean wake deficit reduction increases the averaged power coefficient of VAWT Ⅱ, e.g., up to 22.67% when LS = 6D, TSRⅡ = 1.2, APⅠ = 15°, and TPⅠ = 4TⅠ. In addition, relatively larger pitch amplitudes and smaller pitch periods will further alleviate the negative effect of the wake interference. This study may serve as a reference for designing offshore floating wind farms.

Power improvement of a cluster of three Savonius wind turbines using the variable-speed control method

The average power output of multiple Savonius wind turbines optimally arranged in a cluster is improved significantly compared to that of an isolated turbine due to the coupling effect. Previous investigations focused on the influence of the configuration and the initial phase angles of Savonius turbines operating at the same rotational speed in a cluster. This paper proposes to adopt the variable-speed control method to improve the power output of a three-turbine cluster, and simultaneously avoid the requirement for the accurate initial phase angle settings of the turbines. The Taguchi method is used to optimize the configuration of the cluster. The distances between the centers of adjacent turbines (L1-2, L1-3), the configuration angles (θ1-2, θ1-3), and the combination of rotational directions (RD) are taken as Taguchi experimental factors. The optimal configuration of the cluster is determined to be L1-2 = 2.0D, L1-3 = 2.4D, θ1-2 = 110°, θ1-3 = 110°, and RD = (-,+,-). The influence strength of the factors is ranked as configuration angle, RD, and distance between turbines. In addition, the average power coefficient of the turbines in the optimal cluster is 1.425 times that of an isolated turbine and the tip speed ratios of the three turbines are 1.13, 1.14, and 1.09.

Robust optimization of Savonius-type wind turbine deflector blades considering wind direction sensitivity and production material decrease

Savonius-type vertical axis wind turbine (SWT) has several characteristics appropriate for urban usage: low rotational speed, low noise, easy self-starting; but also has a low power coefficient. One of the methods to improve the SWT efficiency is to use fixed deflector blades, but this makes the SWT performance sensitive to wind direction. This paper performs a robust optimization of deflector blade shape, considering the whole range of wind directions. The objectives are to reduce the required production material and to maximize the annual energy production (which is related to the average power coefficient cPave). Each design efficiency is estimated using 2D CFD transient simulation with GEKO turbulence model. The results show that cPave is increased to cPave = 0.35 using an 8-blade optimized deflector (46% improvement compared to no-deflector) coupled with classical SWT rotor. The 4-blade deflector is inferior with 33% improvement (cPave = 0.32) but with 60% material reduction compared to the previous design. Application of the novel Scooplet-based design achieves a further improvement of cPave = 0.43 and cP,ave = 0.385 for 4-blade and 8-blade deflectors, respectively. A selected optimized design was evaluated using 3D CFD for various aspect ratios (Ar).

Optimization of a vertical axis wind turbine with a deflector under unsteady wind conditions via Taguchi and neural network applications

Vertical axis wind turbines (VAWTs), so named because of their vertical axis of rotation, are a sustainable, opportune, and versatile means of producing energy. Their operation is not dependent on wind direction, making them suitable for use in settings with turbulent and inconsistent winds (e.g., urban locations), and they can be installed at the bottom of towers for easier installation and maintenance. However, unsteady wind may cause a vertical axis wind turbine (VAWT) to operate under drag-controlled conditions and reduce its performance. The power coefficient of a VAWT under unsteady wind conditions is heavily impacted by the tip speed ratio (TSR). Understanding and optimizing TSR is critical to making VAWTs a more viable and attractive option for sustainable energy production. Deflectors have been shown to improve the aerodynamic performance of wind turbines. In the present study, the Taguchi method is used in the experimental design, and a high-fitting neural network (NN) model based on computational fluid dynamics (CFD) data is adopted to predict the optimal mean TSR for a VAWT operation with a deflector. The amplitude and frequency fluctuations of the mean inlet velocity are used to specify the unsteady wind conditions. The results show that the imposed unsteady wind reduces the average power coefficient (Cp-) of the VAWT. By applying the Taguchi method and NN analysis to the impact of unsteady wind conditions, it is found that the mean TSR (TSRmean) is the factor producing the greatest impact on Cp-. The optimal TSRmean is evaluated by the NN model. In light of the recommendation from the NN predictions, the Cp- value from CFD can be improved by up to 3.58 folds under the optimal TSRmean. Furthermore, the relative errors of predicted Cp- values between the NN and CFD simulation are less than 4%, showing the reliability of predictions of the developed NN model in efficiently calculating the optimal operation for a VAWT.

Effects of hydrofoil motion parameters and swing arm parameters on power extraction of a flexible hydrofoil in swing arm mode

This study aimed to numerically investigate the power extraction performance of an oscillating hydrofoil with a time-varying camber in the swing arm mode. The effects of the swing arm length (R), swing arm amplitude (H0), pitching amplitude (θ0), reduced frequency (f*), and flexure amplitude (α) on the average power coefficient (CP‾) and efficiency (η) were investigated. The results revealed that, with an increase in α, the force coefficients were improved, which is beneficial for improving the power extraction capability. At α = 15%, η of the flexible hydrofoil was 38.5%; this represents an increase of approximately 40.5%, as compared to rigid hydrofoils. Further, R and H0 of the swing arm caused variations in the vertical amplitude of hydrofoils, thereby altering the motion velocity and effective angle of attack and further affecting the evolutions of the flow fields and vortices, pressure distribution, and force coefficients. Moreover, the leading-edge vortex was found to separate from the hydrofoils gradually in advance with an increase in θ0, whereas the increase in f* decreased the synchronization between the directions of the force coefficient and motion velocity. Furthermore, it was found that the optimal f*, which could reach peak values of CP‾ and η, increased with θ0.

EFFECTS OF TWO TYPES OF CONTROLLABLE DEFORMATION ON ENERGY EXTRACTION OF A FLEXIBLE HYDROFOIL

Energy extraction capacity of controllably flexible hydrofoil was studied under two identified deformation modes. Deformation modes, flexure parameters (flexure amplitude  and flexure coefficient ) and motion parameters (reduced frequency f* and pitching amplitude 0) were investigated to understand the effects of controllably flexible deformation on energy extraction. The results reveal that deformation modes affect the effective angle of attack and vortex structure, which influence hydrodynamic performance. The energy extraction capacity improves from the deformation mode 2 to the rigid hydrofoil and then to the deformation mode 1. Under the deformation mode 1, lift, moment and power coefficients are increased obviously with the increase of , while they increase slightly with . Power coefficients and efficiency are sensitive to , which influences the development of leading-edge vortices. The flexible coefficient  affects the wake structure, which has less impact on variation of force coefficient. As the increase in f*, averaged power coefficients firstly increase and then decrease. Further, the optimal f* is subjected to 0. Interestingly, a critical reduced frequency f*s, which is generally increase with increasing 0, was found under three modes. The condition that f* > f*s. is a prerequisite for subsequent adjustments of flexure modes and parameters according to different requirement of power coefficient under different tidal currents. The range of high efficiency () is: deformation mode 1 (36.1%<<54.3%) > rigid hydrofoils (34.2%<<41%) > deformation mode 2 (26.9%<<30.3%).

Numerical simulation of flow in hydrokinetic turbine channel to improve its efficiency by using first and second-law efficiency analysis

Hydrokinetic energy uses the flowing water of the riverine systems to generate electrical power. The technology is used to meet the green energy requirements in remote villages, to provide power for the isolated areas and factories with a small utility scale. The present study aims to conduct an analysis of the Egyptian riverine systems for remote areas. Numerical analysis is applied using the URANS model. Verification and validation had been implemented with the proper boundary condition. Five ducted airfoils have been simulated around the hybrid Savonius-Darrieus current turbine as an augmentation technique. The ducted airfoils are NACA-0012, NACA-0015, NACA-0018, NACA-0021, and NACA-0024. The study concluded that the optimal ducted airfoil is the NACA-0015. The hybrid turbine had an average power coefficient of 0.114. Also, the first and the second laws of efficiencies were revealed, for the NACA-0015, of 64.9% and 83.4% respectively.