Hydrokinetic turbine provides a viable option for tapping energy from free-flowing water, making it an attractive contributor to the renewable power landscape. This study investigates the effects of ...blade number and solidity on the performance and wake recovery of a small-scale vertical axis helical hydrokinetic turbine under different tip speed ratios and inflow velocities. Computational fluid dynamics simulations are employed, followed by experimental validation, to analyze power, self-start, torque pulsations, velocity deficit and flow field characteristics. The highest power coefficient is found to be 0.24 for a 4-bladed rotor with 0.3 solidity at a tip speed ratio of 1.0 and inflow velocity of 1.0 m/s. The performance of the studied rotors decreases as inflow velocity increases due to high turbulence experienced, resulting in flow separation. The self-start characteristics are shown to improve with solidity, while torque pulsations are greatly diminished with the increase in number of blades. The wake analysis results show that the velocity deficit and turbulence intensity increase significantly as the number of blades increases. Moreover, the time-averaged streamwise velocity values are observed to reach almost 95 % at a downstream distance of 19–25 times the rotor diameter for investigated rotors.
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•Impact of number of blades on VAHHT rotor performance and wake recovery is explored.•CFD results are validated with the experimental data.•Highest power coefficient is found to be 0.24 for a 4-bladed rotor with 0.3 solidity.•Velocity deficit in wake increased significantly as the blade number increased.•Wake recovery distance is accomplished at 19-25D for investigated rotors.
•Performance of Savonius rotor is improved using the FX74-CL5-140 airfoil-shaped blade.•The impact of a natural airfoil-shaped blade is demonstrated by the CFD approach.•The fluid flow ...characteristics are explored with POD model analysis.•Up to 8.7% and 16.5% enhancement in Cp was observed for different overlap ratios.
The present study introduces a novel rotor configuration with an airfoil-shaped blade, based on the low-speed high-lift FX74-CL5-140 airfoil, for enhancing the performance of the Savonius wind turbine for a practical application in urban areas. The preferment of the present design over the original one with a semicircular shape is confirmed by the sequence of unsteady two-dimensional (2D) numerical simulation. The results demonstrate a new power coefficient peak (up to 16.5 % better than that of the original rotor) could be gained at the tip speed ratio (TSR) of 1.1. The effective working range is further extended to TSR > 0.7 compared to that at TSR > 1.0 in the literature. Insight into the flow dynamic, including pressure, velocity, streamline, and wake analysis, reveals that the thick blade near the overlap region, benefiting in terms of the turbine’s high performance. The airfoil blade increases the momentum energy around the rotor, changes the pressure on the concave side, and varies the origin of the pressure force, leading to an increase in the moment arm with more torque exhibited on the rotor at high TSR. In addition, the proper orthogonal decomposition (POD) analysis is also performed to better understand the flow phenomena behind the rotor. Overall, the present design is beneficial for urban applications because it can enhance the rotor performance without losing the omnidirectional and compactness features.
Blades are the most important components of wind turbines in order to convert wind energy to mechanical energy. This study investigates the aerodynamic performance of Horizontal Axis Wind Turbines ...(HAWTs) with forward and backward swept blades. The effect of the blade sweep direction, the location of the sweep start up and the tip offset on the aerodynamic performance are investigated using a model HAWT with a 0.9 m rotor as the baseline configuration. Changes in power and thrust coefficients with swept blades are investigated for the design tip speed ratio of the baseline wind turbine at a wind speed of 10 m/s. The wind turbine with the forward swept blade that has sweep start up at rss/R = 0.15 and tip offset of d/D = 0.2 has been found to give a remarkable boost to the power output with an increase of about 2.9% over the baseline turbine. The backward swept blade with rss/R = 0.75 and d/D = 0.2 has shown the highest reduction in thrust coefficient, namely 5.4%, at the design tip speed ratio. In conclusion, it is found that the forward swept blades have the ability of increasing the performance while the backward swept blades tend to decrease the thrust coefficient.
•The aerodynamic performances of wind turbines with forward and backward swept blades are investigated.•The blade sweep direction, the location of the sweep start up and the tip offset are varied for the newly designed blades.•Changes in power and thrust coefficients with swept blades are investigated for the design tip speed ratio λ=6.•Forward swept blades can increase the performance while the backward swept blades tend to decrease the thrust coefficient.•It is found that a significant increase in power coefficient can be obtained using forward swept blades.
Renewable electricity is increasingly gaining importance due to the quest for energy security and the harmful effects of fuel-based energy sources. Savonius hydrokinetic turbine (SHKT) can be a ...suitable means to provide electricity using rivers, canals, etc. Optimization of blade shape can play a vital role in enhancing the efficiency of SHKTs. A novel method to generate blade shapes has been proposed in this work using a Bezier curve with six control points. The method involves splitting a blade into two halves and optimizing those separately to simultaneously increase the pressure difference and the normal incoming velocity. The generated blade shapes were studied using a 3D transient computational model, which was validated with the obtained experimental results. Results showed that the blades generated using the proposed model show superior performance compared to conventional semicircular blades as well as the blades generated using four points Taguchi method. The most optimum blade profile achieved a maximum power coefficient of 0.21 at a tip speed ratio of 0.8. The efficiency of this new blade profile was found to be 16.7% higher compared to the semicircular blade, while the best blade using four points method was merely 2.1% more efficient than the semicircular blade.
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In this paper, a three-dimensional numerical study has been conducted by solving the unsteady Reynolds Averaged Navier Stokes equations with shear stress transport (SST) k-omega turbulence model to ...investigate the power production efficiency of a three-bladed H-Darrieus vertical axis wind turbines (HDWT) using S-1046 airfoil under accelerated wind conditions of the cooling tower exhaust system. Aiming to extract the waste energy from the exhaust air, four HDWTs having different aspect ratios were tested by varying the turbine diameter; and the moment and power coefficient values were calculated at tip speed ratios (TSR) in the range of 1.5–3.5. The results showed that the HDWT with a smaller aspect ratio (AR) of 0.44 gives a better power coefficient of 0.294 at TSR 2.5 as compared to other testing conditions. Further, a detailed flow field analysis around the HDWT for different ARs and TSRs has been provided in this paper to discuss the turbine's performance. Finally, a comparative study with the free-stream flow condition showed that HDWT provides 58.5% lower performance than the flow in the exhaust system at lower AR, indicating a positive guided flow effect on the turbine performance under exhaust flow systems.
•Application of H-Darrieus vertical axis wind turbines (VAWT) under cooling tower exhaust air energy recovery systems.•Three-dimensional numerical simulations and analysis of the performance of H-Darrieus VAWT.•Effect of aspect ratio on the performance of H-Darrieus VAWT under cooling tower exhaust air conditions.•Flow Analysis around H-Darrieus VAWT blade under accelerated wind condition.
The present study treats numerically the performance of a straight-bladed, vertical axis, Darieus wind turbine. A two-dimensional (2D), Unsteady Reynolds-averaged Navier–Stokes (URANS) simulations ...were performed out by the solver ANSYS/FLUENT using the sliding mesh method. Four turbulence models, namely the one-equation Spalart– Almaras (SA) model, the two-equation Shear Stress Transport (SST) k-ω, the Transitional Shear Stress Transport (TSST), and the realizable k-ϵ models, with low Reynolds number capabilities, were tested.
The dependency of the power curve upon the torque coefficient and the Tip Speed Ratio (TSR) was evaluated under identical conditions to previously published experimental studies. The results suggest that the realizable k-ϵ model outperformed other turbulence models and matched better with the experimental data. Further numerical investigations were performed to determine the conditions for an optimal performance of the VAWT in question.
A cross-flow HKT can be deployed in rivers and canals having a shallow depth of water to harness the kinetic energy from free stream water. Few studies have been carried out on the hybrid HKT having ...a straight-bladed Savonius rotor in order to enhance the performance of the rotor. However, there is a scope to investigate the effect of radius ratio, attachment angle and water flow velocity on the average power coefficient of a hybrid HKT having a helical-bladed Savonius rotor. Under the present study, the effect of radius ratio, attachment angle and water flow velocity has been analysed numerically on a configuration of a hybrid HKT comprised of three Darrieus rotor blades and two Savonius helical blades. The simulations on different configurations of the hybrid HKT are performed using ANSYS v15. It is observed that the radius ratio and attachment angle significantly affect the energy harnessing capability (average power coefficient) of the hybrid HKT. The optimum radius ratio and attachment angle values for the best-configured hybrid HKT are 0.4 and 90°, respectively. The maximum average power coefficient of the hybrid HKT model with a radius ratio of 0.4 is enhanced by 46.2%, 27.6% and 5.2% compared to models with a radius ratio of 0.2, 0.8 and 0.6, respectively. The hybrid HKT with an attachment angle of 90° is found 4.3% and 4.8%, more efficient than the hybrid configurations with attachment angles of 30° and 150°, respectively. It has been observed that the hybrid HKT is found to have better efficient for low values of water flow velocity. Further, a significant effect of the Savonius blade profile is also found on the performance of the hybrid hydrokinetic turbine rotor.
•Radius ratio and attachment angle affect the performance of hybrid HKT.•The maximum efficiency is obtained for the hybrid HKT model with 0.4 radius ratio.•The hybrid HKT with an attachment angle of 90° is found more efficient.•Performance of hybrid turbine is highly affected with velocity and rotor speed.
The lift-type helical hydrokinetic turbine (LHHT) owns combined capabilities of low torque pulsations and high rotating speed, stimulating the researchers' attention towards power output enhancement ...compared to other cross-flow turbines. The blade tip vortex plays a key role in diminishing the performance; however, it can be countered by lengthening the rotor's blades. In this context, the numerical simulations are performed on the 3D-CFD LHHT model to investigate the influence of aspect ratio considered in the range of 0.75–1.75 on the performance at different tip speed ratios and water velocities. Besides, wake recovery analysis is carried out by measuring velocity deficit at various downstream locations of the rotor under constant 1.0 m/s velocity. The aspect ratio is seen to have a strong influence on power coefficient, torque pulsations and wake recovery as well. The simulation results show that the peak power coefficient is proportional to the aspect ratio and reached a value of 0.228 for 1.75 aspect ratio model, which is 32.5 % superior to the 0.75 model. It is noticed that for an aspect ratio ≥ 1.25, the water velocity recovers 100 % at a distance of 21 times the rotor diameter along the channel where the second machine would be installed.
•Aspect ratio influence on performance and wake recovery is analysed.•Blade tip vortex is observed to decrease with the lengthening of blades.•Aspect ratio should be designed with ≥ 1.5 for CPmax with less torque pulsations.•Wake recovery distance is calculated to deploy second machine along channel.
In the quest for renewable energy sources, kinetic energy available in small water streams, river streams or human-made canals may provide new avenue which can be harnessed by using hydrokinetic ...turbines. Savonius hydrokinetic turbine is vertical axis turbine having drag based rotor and suitable for a lower flow velocity of the water stream. In order to enhance the efficiency of the turbine, this paper aims to analyze the performance of twisted blade Savonius hydrokinetic turbine. Using CFD analysis, an attempt has been made to optimize blade twist angle of Savonius hydrokinetic turbine. The simulation of a twisted Savonius hydrokinetic turbine having two blades has been carried out to investigate the performance. Commercial unsteady Reynolds-Averaged Navier-Stokes (URANS) solver in conjunction with realizable k-ε turbulence model has been used for numerical analysis. Fluid flow distributions around the rotor have been analyzed and discussed. It has been found that Savonius hydrokinetic turbine having a twist angle of 12.5° yields a maximum coefficient of power as 0.39 corresponding to a TSR value of 0.9 for a given water velocity of 2 m/s.
•Savonius rotor having twist angle ranging from 0° to 25° is proposed.•CFD study is carried out for water velocity varied from 0.5 m/s to 2 m/s.•Flow distribution around the Savonius hydrokinetic turbine is discussed.•Effect of twist angle and Reynolds number on performance of rotor was studied.
This investigation aims to study experimentally and numerically the performance of a twisted modified Savonius rotor at various twisting angles. The experiments are conducted in front of a free air ...jet. The computations are performed using the three-dimensional incompressible unsteady Reynolds-Average Navier-Stokes (RANS) equations along with the RNG k-ε turbulence model. The comparison with the present measurements shows good prediction of the RNG k-ε turbulence model to the rotor performance. Furthermore, the power coefficient (CP) and the torque coefficient (CT) at different tip speed ratios (λ) for twist angles ranging from 0° to 180° are predicted under constant aspect ratio of 1.0 and overlap ratio of 0.15. The numerical results show that the maximum power coefficient (CPmax) increases with the increase of twist angle up to an optimum value of 45° and then decreases except for twist angle of 135°. The twisted modified rotor with a twist angle of 45° has the highest CP and CT(0.22 and 0.41, respectively) compared to the other studied twist angles.
•A twisted modified Savonius rotor is experimentally and numerically tested.•Computations based on RNG k-ε turbulence model are performed.•Measurements are carried out on four different shapes of rotors.•The helical modified rotor of 45° twist has the best performance.
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