Ducted Wind Turbine Research Articles

Ducted wind turbines: A review and assessment of different design models

Wind energy technology is progressing at an accelerated pace due to the growing global demand for renewable energy, particularly horizontal axis wind turbines (HAWTs). Ducted wind turbines (DWTs) have emerged as a promising enhancement to traditional horizontal axis wind turbines, demonstrating substantial improvements in efficiency and power output. This study presents a comprehensive evaluation of four distinct designs for DWTs, with a focus on critical factors including efficiency, cost-effectiveness, durability, and environmental sustainability. Among the designs analyzed, the Diffuser configuration emerges as the most advantageous in terms of cost, delivering energy more economically than the Nozzle-Diffuser design. The durability analysis underscores the Diffuser design’s superior longevity, indicated by a durability index of 0.9, reflecting its robust construction and low maintenance demands. Additionally, the Diffuser design is shown to be highly environmentally sustainable, achieving an Environmental Impact Score of 0.91, highlighting its minimal carbon footprint and high recyclability. The study concludes that the Diffuser design offers a balanced and effective solution, combining cost efficiency, durability, and environmental considerations while maintaining competitive efficiency levels.

Enhancing Power Output of Ducted Wind Turbines through Flow Control

This study focuses on the performance enhancement of a ducted small-scale National Renewable Energy Laboratory (NREL) Phase VI wind turbine, utilizing a Wind Lens diffuser. The investigation is conducted at the critical cut-in wind speed of 5 m/s. The research evaluates the integration of passive flow control devices, including Vortex Generators, Microtab, and Slot, strategically positioned across the Wind Lens to augment the mass flow through the rotor. The results indicate significant amplifications in the turbine output of up to 127%, attributable to airflow manipulation across the diffuser, resulting in increased torque and power output. The study highlights the effectiveness of employed flow control devices in managing turbulence and/or flow separation, thereby enhancing aerodynamics, particularly under low wind conditions. A comprehensive analysis of various parameters such as pressure and flow fields, turbulence, and other relevant metrics is conducted to ascertain their collective influence on rotor aerodynamics. The results demonstrate the potential of these passive flow control devices in advancing small-scale wind turbine technology, especially in regions with low wind potential. Moreover, the design simplicity and cost-effectiveness of these passive flow control devices suggest wider applicability in the renewable energy sector, contributing to the reduction of carbon-intensive energy reliance.

Aeroacoustic investigation of a ducted wind turbine employing bio-inspired airfoil profiles

Ducted wind turbines for residential purposes are characterized by a lower diameter with respect to conventional wind turbines for on-shore applications. The noise generated by the rotor plays a significant role in the overall aerodynamic noise. By making modifications to the blade sections of the wind turbine, we can alter the contributions of aeroacoustic noise sources. This study introduces innovative wind turbine blade designs inspired by owl wing characteristics, achieving significant noise reduction without compromising aerodynamic performance. A three-dimensional scan of an owl wing was first employed to derive a family of airfoils. The airfoils were employed to modify the blade of a referenced wind turbine airfoil section at various positions on the blade span to determine a blade operating more efficiently at the tip-speed ratio of the original one. While maintaining the same aerodynamic performance, the bio-inspired profiles show a more uniform pressure coefficient distribution, considerably decreasing in the noise level. Furthermore, this study makes considerable progress in ducted wind turbine design by obtaining an 8 dB noise reduction and a 12% improvement in sound pressure level. An in-depth aerodynamic examination shows a 6.4% rise in thrust force coefficient and optimized power coefficients, reaching a peak at a tip speed ratio of 8, demonstrating improved energy conversion efficiency. The results highlight the dual advantage of the innovative design: significant noise reduction and enhanced aerodynamic efficiency, offering a promising alternative for urban wind generation.

The Ability of Convergent–Divergent Diffusers for Wind Turbines to Exploit Yawed Flows on Moderate-to-High-Slope Hills

Small-to-medium-sized wind turbines operate with wind speeds that are often modest, and it is therefore essential to exploit all possible means to concentrate the wind and thus increase the power extracted. The advantage that can be achieved by positioning the turbine on hilly reliefs, which act as natural diffusers, is well known, and some recent studies can be found on the effects of the characteristics of hilly terrain on the turbine performance. The literature shows numerous investigations on the behavior of ducted wind turbines, i.e., equipped with a diffuser. But so far, there is a lack of studies on the flow acceleration effects achievable by combining natural relief and a diffuser together. In this study, we analyze the performance of a 50 kW ducted turbine positioned on the top of hills of various shapes and slopes, with the aim of identifying the geometric characteristics of the diffuser most suitable for maximizing power extraction. The results show that a symmetrical convergent–divergent diffuser is well suited to exploit winds skewed by the slope of the hill, and therefore characterized by significant vertical velocity components. Due to its important convergent section, the diffuser is able to convey and realign the flow in the direction of the turbine axis. However, the thrust on the diffuser and therefore on the entire system increases dramatically, as does the turbulence released downwind.

Energy Generation Intensity (EGI) of Solar Updraft Tower (SUT) Power Plants Relative to CSP Plants and PV Power Plants Using the New Energy Simulator “Aladdin”

The current investigation provides information about solar updraft tower power plants, SUTPPs (also called solar chimney power plants, SCPPs), which form a unique method of solar-powered electricity production through a ducted wind turbine driven by induced airflow as a result of solar heating. The investigation is conducted using numerical modeling via the system-level simulation tool Aladdin (developed and released freely by the Institute for Future Intelligence, IFI) for solar energy systems, wind energy systems, or the built environment. The Aladdin energy simulator is first evaluated here by comparison with published experimental and numerical results corresponding to the historical 50 kW prototype SUTPP that was successfully tested in Manzanares (Spain) between 1982 and 1989. This prototype has a height of about 195 m for the chimney (the updraft tower) and a radius of about 122 m for the solar heat absorber (the solar air collector or the greenhouse). Next, various climate and performance characteristics are investigated and contrasted for nine different locations around the world with a similar latitude of 24°, which is within the sunbelt, assuming that the same Manzanares SUTPP prototype geometry is employed in these locations. These nine locations are Muscat (Oman), Al Jawf (Libya), Riyadh (Saudi Arabia), Karachi (Pakistan), Ahmedabad (India), Havana (Cuba), Culiacán (Mexico), Dhaka (Bangladesh), and Baise (China). The energy generation intensity (EGI) for the Manzanares-type solar updraft tower power plant in these nine examined locations was between 0.93 kWh/m2 per year (in Baise) and 2.28 kWh/m2 per year (in Muscat). Also, Muscat had the smallest seasonality index (maximum-to-minimum monthly electric output) of 1.90, while Baise had the largest seasonality index of 4.48. It was found that the main limitation of the overall SUTPP energy conversion efficiency is the chimney efficiency (the process of accelerating the air after entering the chimney). This study concludes that solar updraft towers (SUTs) cannot compete with existing mature and modular renewable energy alternatives, particularly photovoltaic (PV) panels, if the aimed use is commercial utility-scale electricity generation. Instead, SUTs may become attractive and achievable if viewed as hybrid-use projects by serving primarily as a large-scale greenhouse area for agricultural applications while secondarily allowing energy harvesting by generating clean (emissions-free) electricity from the incoming solar radiation heat.

Unsteady Reynolds-Averaged Navier–Stokes Simulations of a Ducted Wind Turbine

Abstract An unsteady Reynolds-averaged Navier–Stokes model on body-fitted meshes in a commercial package (SimericsMP+) with a mismatched grid interface is used to study fluid dynamics around a ducted wind turbine. The model is validated by studying turbulent flow past a marine propeller. The nondimensional thrust and torque coefficients are compared against experimental data and results from a large eddy simulation model. Both coefficients are found to be within 3% of experimental results. Following this validation, the impact of different tip speed ratios on the ducted wind turbine's fluid dynamics is assessed. The optimal tip speed ratio is found to be the design value of 3.93 with a maximum power coefficient of 0.465 based on the duct exit area. The corresponding thrust coefficient is found to be 1.02 based on the rotor area. Lower tip speed ratios experience larger flow separation on the duct interior. Higher tip speed ratios decrease the size of the low-velocity region behind the hub. The ducted wind turbine's performance at design conditions is compared to an open rotor. The ducted wind turbine increases the power coefficient by 96% over the open rotor. The impact of hub size on the ducted wind turbine is also studied by simulating a smaller hub with 77% diameter. At the design tip speed ratio, the smaller hub has a power coefficient of 0.417. The maximum power coefficient is found to be 0.446 at a higher tip speed ratio of 4.5.

Numerical and experimental investigation of geometric parameters influence on power generation of INVELOX wind turbine

Wind energy is a key contributor to current transitional trends toward green energy resources. Wind turbines, therefore, act as the main of the wind energy power generation hierarchy, which converts the kinetic energy of wind into electric power. However, low wind velocity is a limiting factor that significantly diminishes the power generation capacity of wind turbines. Alternatively, ducted wind turbines provide a sustainable solution for application in areas with low wind velocity. In the present work, a numerical investigation has been performed to investigate the variation in the power generation capacity of INVELOX with varying geometric parameters. Initially, a numerical investigation of the original INVELOX model was performed to validate the numerical framework and establish the obtained results as a reference. Afterwards, the shape of the funnel, fins/supporting structure, and venturi parameters were varied to analyze their influence on the maximum velocity achieved at the throat. Subsequently, a novel semi-dome concept is added to the model based on numerical results. The results showed that the maximum velocity ratio has been improved from 2.125 to 3.13. Furthermore, power generation capacity was also increased by 3.2 times compared with the original INVELOX design by applying optimized geometric parameters and the semi-dome concept.

DESIGN OF A FLOATING PLATFORM FOR AN INNOVATIVE DUCTED WIND TURBINE

This paper analyses the dynamics loads exerted by waves on a floating offshore platform in the Straits of Messina, (South of Italy), hosting an innovative ducted wind turbine. The force exerted by largest sea waves occurring during lifetime on the floating platform are predicted by the quasi-determinism theory, which foresees what happens if a group of waves of exceptionally large height occurs at a given point in the sea.

Numerical investigation of rotational speed effects on flow separation and boundary layer dynamics in ducted wind turbines

In this paper, we conduct a comprehensive numerical investigation of a ducted wind turbine under various rotational speeds, focusing on aspects such as boundary layer thickness and momentum thickness. Our study utilizes advanced computational fluid dynamics techniques to assess the intricate flow characteristics and aerodynamics of the ducted wind turbine, providing a detailed understanding of its operation under different speed conditions. The primary objectives are to comprehend the effect of the wind turbine’s rotational speed on the boundary layer thickness and the momentum thickness, two crucial parameters influencing the turbine’s performance and efficiency. Our findings reveal a significant correlation between the increase in rotational speed and the growth of flow separation, a phenomenon typically indicated by an expansion in the area of negative wall shear stress. This research contributes valuable insights into the behavior of ducted wind turbines at varying rotational speeds, and the acquired knowledge could potentially be utilized in designing and improving wind turbine systems to achieve better performance and enhanced operational efficiency.

Experimental study of the effect of the duct on dual co-axial horizontal axis wind turbines and the effect of rotors diameter ratio and distance on increasing power coefficient

Due to the recent growing interest in wind energy in urban industry, the present research investigates the increase in power of a micro-wind system using a duct and an auxiliary rotor. The system has the capacity to be employed separately to generate electricity or to be used as part of other systems such as INVELOXes. A duct increases the air flow rate through the turbine, while an auxiliary rotor allows the extraction of the wake kinetic energy. For this purpose, the effect of the duct on increasing wind speed is first studied, and then increasing wind turbine power is investigated. The built duct increases the wind speed up to 42% (from 5 m/s to 7.1 m/s); consequently, the wind turbine power increases over two times. Next, in order to achieve more power, a rotor is placed inside a duct within the front rotor wake. The effect of rotor diameters and the rotors' distance have been investigated by evaluating different configurations to obtain the highest system power. The results show that in the case of adding an auxiliary rotor with the same diameter in a duct, the power coefficient of the rotary part increases to 16%. Moreover, if the two rotors have different diameters (the front rotor has a smaller diameter), the power coefficient will increase up to 13% compared to two rotors with the same diameter. Importantly, as the system is designed to test rotors with independent rotation speed, using the same TSR for both rotors increases the power coefficient of the rotary part by up to 23% compared to the case where two rotors operate at the same rotational speed. Considering the frontal area of the system instead of the rotor area, the power coefficient of the system for ducted wind turbines can also be computed. Accordingly, it is found that its value will be significantly reduced.

Computational fluid dynamic and response surface methodology coupling: A new method for optimization of the duct to be used in ducted wind turbines

Wind energy technology, particularly power generation by wind turbines, has received substantial attention due to resource depletion and global warming concerns. These concerns highlight the importance of conducting studies to enhance their efficiency by increasing their power output. The goal of this work was to combine the RSM (Response Surface Methodology (RSM) with CFD (Computational Fluid Dynamics) to discover the optimal design parameters and conditions for ducted wind turbines. To that purpose, twenty-seven runs were chosen using Central Composite Design (CCD) in the design phase. Duct simulation was performed by employing different dimensional parameters and feeding them into a third-order polynomial that fitted to an eight-order function. The analyzed runs discussed the maximum available wind velocity and power at the throat area of the various designed ducts. The wind-enhanced power and speed were studied under different design parameters, and their effects were discussed. The optimum design conditions to capture maximum power were 0.16 m, 2, and 1.5 for design parameters of the duct's throat diameter, contraction ratio, and length-to-throat diameter ratio, respectively. A good selection of design parameters can increase the outpour power up to six times as a general result. By modeling CFD simulations using the RSM method, it is possible to minimize the time and cost of calculation to find the optimized range for the design parameters of the ducts.

Finding an absolute maximum theoretical power coefficient for ducted wind turbines

This study investigates power coefficients for ducted wind turbines to determine an absolute maximum value corresponding to a maximum ideal power output. A maximum power coefficient using the rotor area in the available kinetic energy is still an open question in the research community. Here, the available kinetic energy of a free stream uses the largest device area, diffuser outlet, funnel inlet, and virtual diffuser outlet areas in the power coefficient calculation. The virtual diffuser outlet is defined as the downstream location at which the static pressure of the fluid inside the stream tube recovers to the pressure of the free stream flow. This study performs a one-dimensional analysis based on the continuity, momentum, and energy principles and the Euler Turbomachinery equation. The results show the absolute maximum power coefficient of 0.384 using the virtual diffuser outlet area in the available kinetic energy calculation. Another finding is that both the maximum ideal power output and the cp = 0.384 happen at the same value of the rotor thrust coefficient, CT,R≈ 2/3. The power coefficient based on the rotor area is more convenient for idealized bare turbines; therefore, the power coefficient based on the virtual diffuser outlet area applies only to ducted wind turbines.

Single-objective optimization design of convergent-divergent ducts of ducted wind turbine using RSM and GA, to increase power coefficient of a small-scale horizontal axis wind turbine

Single-objective optimization design of convergent-divergent ducts of ducted wind turbine using RSM and GA, to increase power coefficient of a small-scale horizontal axis wind turbine

Numerical and experimental investigation of a wind rotor equipped with wind catcher system

Abstract Wind energy is a key driver for the transformation towards a sustainable energy system. From a certain point of view, the main parameter is to increase the turbines' height and the rotor's size to improve the economic aspect and performance. On the other hand, ‘ducted wind turbines’, which can significantly improve the performance of smaller wind turbines, are attracting much attention. The objective is to create system compatible with urban environments and at the same time improve the efficiency of ducted wind turbines. This article studies a configuration, namely a wind turbine equipped with a wind catcher system, by studying it both experimentally and numerically. First, the tests are carried out on the system without inserting the wind rotor. Then the results of the developed model are compared via experimental tests, showing that it is possible to accept wind from all directions and from different heights by using the wind collector system and the cones. The results also show that the maximum wind speed increases by 2.5 times in the middle of the cylindrical part where the turbine is planned to be placed. Finally, the effects of inserting a vertical axis wind turbine inside the cylindrical part of the system on its power coefficient are studied. The results show that the system significantly improves the maximum power coefficient of the turbine.

Performance analysis of various types of ducted wind turbines – A review

Performance analysis of various types of ducted wind turbines – A review

Novel INVELOX design with unique intake to improve wind capturing mechanism

Renewable energy sources, such as wind energy, have been utilized to mitigate climate change. INVELOX is a ducted wind turbine (DWT) consisting of an omnidirectional intake and a Venturi section. The INVELOX original design was found to have multiple points of high friction points that restrict the wind flow inside the INVELOX. In addition, intake in the original design allows the wind stream to escape the INVELOX, thus, limiting its performance. An improved INVELOX model was developed to overcome high wind friction points in the original design and to overcome INVELOX intake limitations by a novel intake mechanism. Computational fluid dynamics (CFD) was used to simulate the improved model in a similar setup to the original design. The simulation methodology is divided into three main stages: validation, analysis, and improvement of the original design. Results showed that the novel intake design improved the average wind speed at the Venturi section to 18.6 m/s from the initial 6.7 m/s wind stream. This performance was also maintained at higher wind speeds, unlike the original INVELOX design.

High-Order Large Eddy Simulations of a Wind Turbine in Ducted and Open-Rotor Configurations

Abstract High-order large eddy simulations are performed to study the performance and flow fields of a ducted wind turbine (DWT) operating at different tip speed ratios. To evaluate the effects of the duct, simulations with the same tip speed ratios are also performed on the corresponding open-rotor turbine. It is found that the ducted turbine consistently obtains higher power outputs than the open-rotor counterpart, and the duct itself enhances flow turbulence and blade trailing-edge vortices but weakens tip and hub vortices. Flow bifurcation is observed at the largest tip speed ratio and is identified to be caused by blade blockage effects. Comparative simulations are also performed on both turbines under different yaw angles. It is noticed that the ducted configuration is insensitive to small yaw angles and maintains higher power outputs than the open-rotor configuration at all yaw angles. Moreover, it is observed that the wakes of both configurations recover more quickly as the yaw angle increases.

Numerical and Experimental Investigation of the Ducted Wind Turbine Performance With and Without Obstacle Plates

Numerical and Experimental Investigation of the Ducted Wind Turbine Performance With and Without Obstacle Plates

An innovative design of INVELOX wind turbine: a numerical study on the effects of implementing long flange and Venturi holes

There is a global interest in renewable energy resources such as wind energy. INVELOX (increased velocity) is an innovative ducted wind turbine system. Some research has been performed to improve the efficiency of this machine by various geometrical modifications. Two ideas are presented and numerically analyzed in the present research to study their effects on the wind velocity when approaching the wind turbine, and consequently, on the wind turbine efficiency. In one of them, a relatively long flange is added to the original design, and in the other one, a pair of holes is considered in the venture to try to increase the mass flow rate of wind when reaching the turbine. Three various sizes of holes are studied here. The results reveal that using the long flange leads to an increment in the maximum wind velocity (about 15.45%) and more than 176% increase in the harvested power. In addition, the pair of holes in the Venturi with a diameter of 35 cm results in a slight improvement in the harvested power. For the first time, the turbine has been modeled inside the Venturi. A comparison between the results for the INVELOX, including the turbine, and that of the turbine in the free stream indicates that implementing INVELOX leads to 3.14 times more power generation.

Numerical Study of the Effect of Flap Geometry in a Multi-Slot Ducted Wind Turbine

One possible way to harness wind more efficiently in low-wind urban areas is to place wind turbines inside a duct. A known issue of such approach is due to the flow separation that can occur at the diffuser walls. This can be avoided using a channelled structure consisting of a duct and a flap, also known as a multi-slot system. The present work describes the effects of a flap geometry on the turbine performance, through computational fluid dynamics (CFD). Four flaps based on airfoils, with different thicknesses and cambers, were evaluated. It was found that thinner and more cambered flaps produce higher wind turbine performance, showing power augmentations up to 2.5 compared to a bare turbine. A comparison between the multi-slot design and a single-piece duct of the same geometry was also performed, showing that the multi-slot design is more efficient if the flow is maintained attached to the flap.