Diffuser augmented wind turbines: review and assessment of theoretical models (original) (raw)
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Analytical models for concentrator and diffuser augmented wind turbines: A review
International Journal of Smart Grid and Clean Energy
Energy from wind is envisaged as one of the second largest inexhaustible and clean green energy resource around the world. It has the potential of replacing fossil fuel based energy, which has high carbon dioxide emissions contributing to global warming. In addition, wind energy can provide power in remote areas which are not connected to the national electricity grids. In wind energy technology, wind turbines convert wind energy to electricity. However, most commercially available wind turbines are made for wind speeds greater than 5m/s, therefore fail to operate in areas with low wind speeds. Innovative ways of improving the wind power output include the use of concentrators and diffusers. Although there are notable experimental and computational fluid dynamics researches on concentrator diffuser augmented wind turbines (CDAWTs), attempts to develop analytical to semi-empirical models are extremely scarce. Only analytical models for diffuser augmented wind turbines (DAWTs) dominate in literature. In this work, a comprehensive review of previously developed analytical models is presented. The information will assist researchers to comprehend current research efforts and to discover the knowledge gaps so as to develop accurate analytical models that incorporate CDAWTs structure. In this review, existing analytical models fail the validity tests due to their underlying assumptions which give incomplete explanations of the major flow phenomena. Once all these issues are considered, an analytical model that predicts accurately the power output of CDAWTs can be developed. This will be a step in the right direction in designing and constructng the CDAWTs for commercialization.
Performance Investigation of Diffuser Augmented Wind Turbine
2017
Renewable energy resources are becoming an increasingly important part of our total energy demands due to the depletion of fossil fuels and the emergence of global warming. Wind turbines are one type of renewable resource that is very usual in the offshore site has a stronger and steadier wind speed which can produce more energy. It is a fact that wind power is the best dilute and unpredictable source of energy that works with efficiency of great importance in the conversion of this energy to electricity. It is a common practice to place wind turbines on ridges and hills to increase wind velocity over that of free stream. If a device (shroud) can be added to a bare turbine to increase wind velocity just as our research was to add shrouds by means of computer simulations to encase the “bare turbine” thereby increasing efficiency. Our goal is to find a particular shroud that maximized air mass flow through the turbine beyond the best bare turbine operational conditions. In this analys...
Simulation of Diffuser Augmented Wind Turbine performance
2016 World Congress on Sustainable Technologies (WCST), 2016
The main objective of this research is to optimize the diffuser design of Diffuser Augmented Wind Turbine (DAWT). Specifically, this study investigates the effect of different shapes of diffusers to develop the suitable diffuser parameter for the wind turbine power enhancement. For that purpose, two diffuser cases have been recommended as an effective design in increasing wind speed, using a validated model of a small commercial wind turbine (AMPAIR-300) in it were developed and each case is simulated and analyzed using design software Solid-works and Computational Fluid Dynamic (CFD) software Fluent-ANSYS-15, As per the study, for diffuser case-1,the diffuser splitter degrades the diffuser effect when its open angle higher than the diffuser open angle, for diffuser case-2 the diffuser splitter enhance the diffuser effect when its open angle lower than diffuser open angle, also adding inlet shroud directs the wind flow into the inlet of diffuser and the diffuser flange effect on the power enhancement was significant and also its induced axial load was significant, and it is recommended to study the optimum dimension of inlet shroud, diffuser flange and diffuser splitter to minimize the coefficient of thrust and to enhance the coefficient of power.
Modeling and Analysis of Diffuser Augmented Wind Turbine
Renewable energy resources are increasingly becoming an important percentage of our total energy demands, largely due to the depletion of fossil fuels and the emergence of global warming. Wind turbines are one type of renewable resource that is very apparent in the South Texas region. The fact that wind power is at best a dilute and unpredictable source of energy makes efficiency of great importance in the conversion of this energy to electricity. Our research was to add shrouds by means of computer simulations to encase the “bare turbine”, thereby increasing efficiency. Our goal was to find a particular shroud that maximized air mass flow through the turbine beyond the best of bare turbine operational conditions.
Article A Multi-Element Diffuser Augmented Wind Turbine
2014
A new class of diffuser augmented wind turbines (DAWTs) is presented. The new diffuser concept exploits aerodynamic principles for the creation of high-lift airfoil configurations known from the aircraft industry. Combining this with our objective of obtaining a compact power-efficient design has enabled creation of a family of DAWT designs with energy capture potentials which exceed the power efficiency based on the diffuser exit area by 50%. The paper presents the 1D momentum theory governing the DAWTs, and discusses upper limits for power extraction, similar to the Betz limit applicable for bare Horizontal-Axis Wind Turbines (HAWTs). Inviscid axisymmetric panel code calculations are then used to drive the diffuser design towards higher power coefficients. Axisymmetric actuator disk Navier-Stokes calculations reveal the types of stall that inhibit the functionality of the ideal inviscid optimum, leading the design towards the new class of DAWTs. DAWT performance has been differently measured over time, creating confusion. Proper comparison with performance of existing DAWT designs is therefore emphasized. This involves reference to established literature results, and recalculation of earlier DAWT designs in an attempt to project all results onto a common metric.
A Multi-Element Diffuser Augmented Wind Turbine
Energies, 2014
A new class of diffuser augmented wind turbines (DAWTs) is presented. The new diffuser concept exploits aerodynamic principles for the creation of high-lift airfoil configurations known from the aircraft industry. Combining this with our objective of obtaining a compact power-efficient design has enabled creation of a family of DAWT designs with energy capture potentials which exceed the power efficiency based on the diffuser exit area by 50%. The paper presents the 1D momentum theory governing the DAWTs, and discusses upper limits for power extraction, similar to the Betz limit applicable for bare Horizontal-Axis Wind Turbines (HAWTs). Inviscid axisymmetric panel code calculations are then used to drive the diffuser design towards higher power coefficients. Axisymmetric actuator disk Navier-Stokes calculations reveal the types of stall that inhibit the functionality of the ideal inviscid optimum, leading the design towards the new class of DAWTs. DAWT performance has been differently measured over time, creating confusion. Proper comparison with performance of existing DAWT designs is therefore emphasized. This involves reference to established literature results, and recalculation of earlier DAWT designs in an attempt to project all results onto a common metric.
International Journal of Wind Engineering and Industrial Aerodynamics, 2023
The study investigates the soundness of a popular uncoupled design strategy for diffuser-augmented wind turbines (DAWTs), namely the use of an annular wing to enclose an existing open-rotor. To this aim, the paper presents a numerical analysis of the NREL-Phase-VI rotor enclosed into a shroud whose cross-section consists of the Selig-S1223 airfoil. Particular attention is devoted to the analysis of the blade pressure fields, velocity triangles, blade forces, tip-vortex and wake development. The data show that the duct induces a gain in the rotor inlet axial velocity and, therefore, in the local flow-angle. Consequently, the blade forces, the extracted work, and the risk of flow separation considerably rise. Thanks to the simultaneous increase in the ingested mass flow rate and extracted work, the DAWT experiences a higher power coefficient (C_{P,exit}) which, however, would be further improved if a coupled design-procedure was used. Indeed, in the present case, the maximum C_{P,exit} is obtained for the wind-speed value corresponding to the duct optimal flow behaviour. However, in this condition, the rotor operates at off-design with an extensive flow-separation on the blade suction-side. Finally, while the inefficiencies magnitude is specific of the analysed case, the conceptual relevance of the achievements remains valid in general.
International Journal of Mechanical Engineering and Robotics Research
A diffuser-driven wind turbine (DAWT) was used in this paper to increase the efficiency of small-sized horizontal axis wind turbines (HAWTs) by surrounding them with a suitable distributor. The study included two steps: first, knowing the effect of the number of blades inside the diffuser in three configurations (2-blades, 3blades, and 4-blades), and secondly, showing the effect of the turbine position inside the diffuser in three cases based on the largest increase in wind speed in the diffuser. The numerical simulation investigation was carried out using 3D CFD ANSYS software by methods that rely on the SST k-ω turbulence model. The performance of the models was evaluated in terms of strength and aerodynamics coefficients, by calculating power coefficients CP. The study showed that the turbine at the entrance to the diffuser gives the highest performance compared to other cases. Where the increase at the inlet the power coefficient of the turbine the diffuser is (22% and 14%) compared to its position in the middle of the diffuser and the end of the diffuser, respectively.
Optimization of the Power Output of a Bare Wind Turbine by the Use of a Plain Conical Diffuser
Sustainability
A plain conical diffuser is optimized to augment the wind speed at the throat of the diffuser. The diffuser is used in the construction of a diffuser augmented wind turbine (DAWT) to augment the power output of a bare wind turbine (BWT). Experiments with empty conical diffusers were done to determine optimum geometrical parameters for the diffuser to achieve maximum wind speed augmentation. Using the obtained optimum geometrical parameters, an optimized plain conical DAWT was designed, constructed, and field tested. A twin decentralized wind energy system which comprised a BWT and the optimized plain conical DAWT was erected. The electrical power output from these systems was measured and compared. The optimized plain conical DAWT reduced the cut-in wind speed of a BWT from 2.5 m/s to 1.6 m/s. The power output was increased by a factor of 2.5. This power output is comparable to that of flanged diffusers. However, flanged-DAWTs are more inert due to the addition of the flange. Its re...
International Journal for Research in Applied Science and Engineering Technology, 2018
Diffusers have been used to augment the wind speed in diffuser augmented wind turbines. However, there is no known method to estimate the wind speed augmentation by these diffusers. This study presents a mathematical model that estimates the wind speed augmentation by empty conical diffusers for use in diffuser augmented wind turbines (DAWT). The model is used by DAWT wind energy systems engineers in optimizing the power output of the DAWT. The model is based on the diffuser length (L), diffuser expansion angle (θ) and the diffuser inlet diameter (D). The model equation and the experimental data are correlated with R 2 = 0.9751 and RMSE = 0.034. It was shown that the diffuser expansion angle (θ), a predictor contributes more to the desired output as compared to the non-dimensional length (L/D) .