Performance investigation of cavity shaped blade on H-Darrieus wind turbine in built environmental condition
14 Feb 2022-Energy Sources Part A-recovery Utilization and Environmental Effects-pp 1-17
TL;DR: In this paper , the effect of circular cavity on aerodynamic performance of the H-Darrieus rotor is investigated using a subsonic wind tunnel test facility to check which side cavity on the airfoil (inner or outer side) is beneficial in terms of the rotor's static and dynamic performances.
Abstract: This present investigation is carried out to improve the performance of H-Darrieus wind turbine in the built environment, where it mostly experiences low wind speed. Here the effect of circular cavity on aerodynamic performance of the rotor is investigated using a subsonic wind tunnel test facility to check which side cavity on the airfoil (inner or outer side) is beneficial in terms of the rotor’s static and dynamic performances. For this, S1046 and NACA 0021 airfoil blades are considered at various low wind speeds of 5, 6 and 7 m/s for different rotor aspect ratios. A Computational Fluid Dynamics (CFD) study is also simultaneously conducted to realize the intrinsic flow physics of the cavity airfoil blade profile. Results show that inner surface cavity on both the blades improves their self-starting ability but only at 5 m/s wind speed, which is not so when wind speed is 7 m/s at which NACA 0021 blade without cavity performs better. Again, NACA 0021 blade without cavity exhibits the highest performance of all the considered blade shapes, for which the highest power coefficient of 0.15 is achieved at a tip speed ratio of 1.25 and wind speed 6 m/s. At wind speed 7 m/s, the NACA 0021 blade rotor having outside cavity has a lower maximum power coefficient but wider operating range than that of NACA 0021 blade without cavity. CFD results show that H-Darrieus rotor having NACA 0021 blades at 30° azimuthal angle with circular cavity at 1/4th chord distance from its leading edge located at its inner surface, can generate higher lift force. However, circular cavity will be useful for starting performance of H-Darrieus rotor, which is not so for its dynamic performance, although operating range is improved.
TL;DR: In this article , the authors incorporated protrusions in the leading edge of the NACA 4415 airfoil as a passive flow control measure on the wind turbine blades for a horizontal axis wind turbine (HAWT) to investigate its performance.
Abstract: In the present study, protrusions in the leading edge of the NACA 4415 airfoil were incorporated as a passive flow control measure on the wind turbine blades. Three airfoil models: unmodified leading-edge (ULE), spherical leading-edge protrusion (SLEP), and triangular leading-edge protrusion (TLEP), were investigated experimentally. Thereafter, CFD investigations were carried out using ANSYS 14.0 simulation tool to observe the flow characteristics around the airfoils. Further, LEP-based passive design was applied on a horizontal axis wind turbine (HAWT) to investigate its performance. An amplitude (A) of 1% of the chord length (C) was considered as the height of protrusion, while a distance of 0.25C was maintained between the protrusions to fabricate the experimental models. The study was performed at a low Reynolds number (Re) of 1.5 × 105 for a wide angle of attack (α) of 0°–20°. The experimental results demonstrate that the SLEP model has a higher lift coefficient at α ≥ 18°, whereas the TLEP model performs poorly when compared with the ULE model. The instantaneous lift coefficient plot indicates that the SLEP model generates a more stable force at a higher angle of attack. The computational analysis reveals that a larger primary circulation (extended till 0.2C) is observed in the ULE model at a post-stall angle of attack (α = 18°), indicating early flow separation. Whereas, in the SLEP and TLEP models, it is extended to 0.70C and 0.54C, respectively, indicating the best flow controlling measures achieved by using the SLEP model. The investigations of HAWT rotors with LEP revealed that SLEP HAWT exhibit 8.2% more power coefficient than ULE HAWT.
TL;DR: In this article , the performance of the H-Darrieus VAWT having NACA 0018 airfoil by use of semi-cylindrical attachments at the trailing edge and hybridization using two bladed S-Savonius rotor with zero overlap conditions was examined at a low wind speed of 4 m/s.
Abstract: Vertical axis wind turbines (VAWTs) work efficiently in low wind speed regions and varying wind directions like urban environments due to their omnidirectional capability. The current study examines experimentally the performance of the H-Darrieus VAWT having NACA 0018 airfoil by use of semi-cylindrical attachments at the trailing edge and hybridization using two bladed S-Savonius rotor with zero overlap conditions. The rotor's static torque and dynamic performances are investigated at a low wind speed of 4 m/s. The results show that the semi-cylindrical attachment increases the range of positive static torque. The static torque of Darrieus with attachment at 90° inside is more consistent, which enhances the starting capability of the Darrieus turbine with a static torque coefficient of 0.031, which is 29.7 % higher than a simple Darrieus turbine. The hybrid configuration shows maximum dynamic torque only at the 90° azimuthal position. The power coefficient of all configurations with attachments is lower than simple Darrieus due to drag created by attachments. The power coefficient value of 0.03 for hybrid configuration is the highest, with a wide range of tip speed ratio (TSR).
TL;DR: In this article, a combined experimental and computational study into the aerodynamics and performance of a small scale vertical axis wind turbine (VAWT) was presented, where wind tunnel tests were carried out to ascertain overall performance of the turbine and two-and three-dimensional unsteady computational fluid dynamics (CFD) models were generated to help understand the aerodynamic of this performance.
Abstract: This paper presents a combined experimental and computational study into the aerodynamics and performance of a small scale vertical axis wind turbine (VAWT). Wind tunnel tests were carried out to ascertain overall performance of the turbine and two- and three-dimensional unsteady computational fluid dynamics (CFD) models were generated to help understand the aerodynamics of this performance. Wind tunnel performance results are presented for cases of different wind velocity, tip-speed ratio and solidity as well as rotor blade surface finish. It is shown experimentally that the surface roughness on the turbine rotor blades has a significant effect on performance. Below a critical wind speed (Reynolds number of 30,000) the performance of the turbine is degraded by a smooth rotor surface finish but above it, the turbine performance is enhanced by a smooth surface finish. Both two bladed and three bladed rotors were tested and a significant increase in performance coefficient is observed for the higher solidity rotors (three bladed rotors) over most of the operating range. Dynamic stalling behaviour and the resulting large and rapid changes in force coefficients and the rotor torque are shown to be the likely cause of changes to rotor pitch angle that occurred during early testing. This small change in pitch angle caused significant decreases in performance. The performance coefficient predicted by the two dimensional computational model is significantly higher than that of the experimental and the three-dimensional CFD model. The predictions show that the presence of the over tip vortices in the 3D simulations is responsible for producing the large difference in efficiency compared to the 2D predictions. The dynamic behaviour of the over tip vortex as a rotor blade rotates through each revolution is also explored in the paper.
TL;DR: In this article, the performance of the straight Darrieus turbine (H-rotor) was investigated for 20 different airfoils (Symmetric and Non-symmetric) by two-dimensional Computational Fluid Dynamics in order to maximize output torque coefficient and output power coefficient (efficiency).
Abstract: Since millenaries humans have attempted to harness the wind energy through diverse means. Vertical axis wind turbines (VAWTs) were originally considered as very promising, before being superseded by the present, horizontal axis turbines. For various reasons, there is now a resurgence of interests for VAWTs, in particular Darrieus turbines. Using modern design tools and computational approaches, it should be possible to increase considerably the performance of traditional VAWTs, reaching a level almost comparable to that of horizontal axis turbines. Since VAWTs show many specific advantages (compact design, easier connection to gears/generator, easier blade control if needed, lower fatigue…), it is important to check quantitatively the efficiency of such turbines. This is the purpose of the present work, starting from the standard, straight Darrieus turbine (H-rotor). The aerodynamic investigation will be carried out for 20 different airfoils (Symmetric and Non-symmetric) by two-dimensional Computational Fluid Dynamics in order to maximize output torque coefficient and output power coefficient (efficiency). A considerable improvement of the H-rotor Darrieus turbine performance can be obtained in this manner.
••01 Feb 2007
TL;DR: In this paper, a case study is presented based upon the use of the widely used and well documented, symmetrical NACA 0012 turbine blade profile, and it is shown that a lightly loaded, three-bladed rotor always has the potential to self start under steady wind conditions, whereas the starting of a twobladed device is dependent upon its initial starting orientation.
Abstract: Darrieus-type vertical axis wind turbines have a number of potential advantages for small-scale and domestic applications. For such applications, the issues of cost and reliability are paramount and hence simplicity of design of the structure, the generator, and any control system is vital. A particular concern relating to Darrieus turbines is their potential to self-start. If, as has been suggested by several authors, they require external assistance to start then much of their advantage is lost. The purpose of the study described here is, therefore, to investigate their starting performance through the development and validation of computational simulation and to determine the parameters that govern the capability to self-start. A case study is presented based upon the use of the widely used and well documented, symmetrical NACA 0012 turbine blade profile. It is shown that a lightly loaded, three-bladed rotor always has the potential to self start under steady wind conditions, whereas the starting of a two-bladed device is dependent upon its initial starting orientation.
TL;DR: In this article, a comparison between ANSYS Workbench and Gambit meshing tools for the numerical modeling is performed to summarize a final numerical sequence for the Darrieus rotor performance.
Abstract: Vertical axis wind turbines like the Darrieus turbine appear to be promising for the conditions of low wind speed, but suffer from a low efficiency compared to horizontal axis turbines. A fully detailed numerical analysis is introduced in this work to improve the global performance of this wind turbine. A comparison between ANSYS Workbench and Gambit meshing tools for the numerical modeling is performed to summarize a final numerical sequence for the Darrieus rotor performance. Then, this model sequence is applied for different blade airfoils to obtain the best performance. Unsteady simulations performed for different speed ratios and based on URANS turbulent calculations using sliding mesh approach. Results show that the accuracy of ANSYS Workbench meshing is improved by using SST K-omega model but it is not recommended for other turbulence models. Moreover, this CFD procedure is used in this paper to assess the turbine performance with different airfoil shapes (25 airfoils). The results introduced new shapes for this turbine with higher efficiency than the regular airfoils by 10%. In addition, blade pitch angle has been studied and the results indicated that the zero pitch angle gives best performance.
TL;DR: In this article, the impact of solidity and number of blades on the aerodynamic performance of 2-, 3-and 4-bladed Darrieus H-type vertical axis wind turbines was analyzed.
Abstract: The current study systematically analyzes the impact of solidity (σ) and number of blades (n) on the aerodynamic performance of 2-, 3- and 4-bladed Darrieus H-type vertical axis wind turbines (VAWTs). Solidity varies within the wide range of 0.09–0.36. A large number of operational parameters, i.e., tip speed ratio (λ), Reynolds number (Re), turbulence intensity and reduced frequency (K) are investigated to provide a deeper insight into the impact of σ and n on the dynamic loads on blades, the turbine performance and the wake. High-fidelity unsteady Reynolds-averaged Navier-Stokes (URANS) simulations, extensively validated with experiments, are employed. The results show that the turbine optimal tip speed ratio (λopt) is invariant to a newly-introduced parameter ‘ σ λ 3 ’, regardless of the turbine geometrical and operational characteristics. In addition, a new correlation is derived to estimate λopt as a function of σ, which can also be employed to predict the optimal σ for a turbine with a given λ. It is also found that: (i) for constant-speed urban VAWTs, which due to the low mean wind speed in the urban environment, frequently operate at moderate to high λ, a relatively-low σ is optimal; (ii) an optimal VAWT is a moderately-high-solidity variable-speed rotor maintaining a relatively-low λ, where due to the large blade chord length the resulting Re and K are favorably high; (iii) within the turbine optimal operational range, turbine power coefficient (CP) is almost independent of n. The present findings support the optimal aerodynamic design of small-to large-scale VAWTs.
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