Performance Of Ducted Wind Turbines Research Articles

Ground effect for ducted wind turbines: A computational study

Ducted wind turbines (DWTs) can take the advantage of ground effect (GE) when installed close to urban areas. To this aim, a parametric study to investigate the aerodynamic performance of DWTs in relation to three different ground distances are investigated. The flow around a commercial DWT model using a simplified duct actuator disc (AD) model based on Reynolds Averaged Navier-Stokes (RANS) equations is performed. The results indicate that DWTs placed close to the ground will lead to increased mass flow rate the turbine plane, and thereby improving the aerodynamic performance. However, the additional ground force leads to an asymmetric flow-field at the turbine plane, which will ultimately induce unsteady forces on the DWT system. The present analysis will serve as a strong recommendation to address siting issues for DWT manufacturers.

Ducted wind turbines in yawed flow: a numerical study

Abstract. Ducted wind turbines (DWTs) can be used for energy harvesting in urban areas where non-uniform flows are caused by the presence of buildings or other surface discontinuities. For this reason, the aerodynamic performance of DWTs in yawed-flow conditions must be characterized depending upon their geometric parameters and operating conditions. A numerical study to investigate the characteristics of flow around two DWT configurations using a simplified duct-actuator disc (AD) model is carried out. The analysis shows that the aerodynamic performance of a DWT in yawed flow is dependent on the mutual interactions between the duct and the AD, an interaction that changes with duct geometry. For the two configurations studied, the highly cambered variant of duct configuration returns a gain in performance by approximately 11 % up to a specific yaw angle (α= 17.5∘) when compared to the non-yawed case; thereafter any further increase in yaw angle results in a performance drop. In contrast, performance of less cambered variant duct configuration drops for α>0∘. The gain in the aerodynamic performance is attributed to the additional camber of the duct that acts as a flow-conditioning device and delays duct wall flow separation inside of the duct for a broad range of yaw angles.

A design of experiment approach as applied to the analysis of diffuser-augmented wind turbines

Since the 1930s ducted-wind-turbines have received considerable attention due to the possibility of obtaining a significant increase in the extracted power compared to an open turbine with the same rotor swept area. The incomplete knowledge of the flow phenomena occurring in these devices and the large design-space to be explored generally hampers the development of an effective and robust design-procedure. This work investigates the performance of ducted wind turbines through a fully automated analysis procedure based on a Computational-Fluid-Dynamics-Actuator-Disk approach. The method duly takes into account the effects of the design parameters, the rotor-duct coupling, the wake rotation and expansion, and the spanwise variability of the rotor load. A Design-of-Experiment analysis is carried out to quantify the impact of the change of all geometric parameters and their mutual interactions. The latter explicitly account for the simultaneous variation of all design parameters. As such, it is a powerful pre-design tool that allows to reduce and confine the design space. It is found that the chord and stagger angle of the duct contribute more than 85% to the improvements of the turbine performance, while the effects of the thickness are negligible. Finally, the sensitiveness of the performance to the variation of the operating conditions is also analysed revealing that the optimal configuration is also the most robust.

Effects of yawed inflow on the aerodynamic and aeroacoustic performance of ducted wind turbines

Ducted Wind Turbines (DWTs) can be used for energy harvesting in urban areas where non-uniform inflows might be the cause of aerodynamic and acoustic performance degradation. For this reason, an aerodynamic and aeroacoustic analysis of DWTs in yawed inflow condition is performed for two duct geometries: a baseline commercial DWT model, DonQi®, and one with a duct having a higher cross-section camber with respect to the baseline, named DonQi D5. The latter has been obtained from a previous optimization study. A numerical investigation using Lattice-Boltzmann Very-Large-Eddy Simulations is presented. Data confirm that the aerodynamic performance improvement, i.e. increase of the power coefficient, is proportional to the increase of the duct thrust force coefficient. It is found that, placing the DWT at a yaw angle of 7.5°, the aerodynamic performances of the DonQi D5 DWT model are less affected by the yaw angle. On the other hand, this configuration shows an increase of broadband noise with respect to the baseline DonQi® one, both in non-yawed and yawed inflow conditions. This is associated to turbulent boundary layer trailing edge noise due to the turbulent flow structures developing along the surface of the duct.

Characterization of aerodynamic performance of ducted wind turbines: A numerical study

AbstractThe complex aerodynamic interactions between the rotor and the duct has to be accounted for the design of ducted wind turbines (DWTs). A numerical study to investigate the characteristics of flow around the DWT using a simplified duct–actuator disc (AD) model is carried out. Inviscid and viscous flow calculations are performed to understand the effects of the duct shape and variable AD loadings on the aerodynamic performance coefficients. The analysis shows that the overall aerodynamic performance of the DWT can be increased by increasing the duct cross‐sectional camber. Finally, flow fields using viscous calculations are examined to interpret the effects of inner duct wall flow separation on the overall DWT performance.

Multi-element ducts for ducted wind turbines: a numerical study

Abstract. Multi-element ducts are used to improve the aerodynamic performance of ducted wind turbines (DWTs). Steady-state, two-dimensional computational fluid dynamics (CFD) simulations are performed for a multi-element duct geometry consisting of a duct and a flap; the goal is to evaluate the effects on the aerodynamic performance of the radial gap length and the deflection angle of the flap. Solutions from inviscid and viscous flow calculations are compared. It is found that increasing the radial gap length results in an augmentation of the total thrust generated by the DWT, whereas a larger deflection angle has an opposite effect. Reasonable to good agreement is seen between the inviscid and viscous flow calculations, except for multi-element duct configurations characterized by large flap deflection angles. The viscous effects become stronger at large flap deflection angles, and the inviscid calculations are incapable of taking this phenomenon into account.

Towards improving the aerodynamic performance of a ducted wind turbine: A numerical study

This paper aims to study the aerodynamic performance of ducted wind turbines (DWT) using inviscid and viscous flow calculations by accounting for the mutual interaction between the duct and the rotor. Two generalized duct cross section geometries are considered while the rotor is modelled as an actuator disc with constant thrust coefficient. The analysis shows the opportunity to significantly increase the overall aerodynamic performance of the DWT by a correct choice of the optimal rotor loading for a given duct geometry. Present results clearly indicate that the increased duct cross section camber leads to an improved performance for a DWT. Finally, some insights on the changes occurring to the performance coefficients are obtained through a detailed flow analysis.

Effects of the duct thrust on the performance of ducted wind turbines

This work investigates the performance of ducted wind turbines (DWTs) through the axial momentum theory (AMT) as well as through a semi-analytical approach. Although the AMT points out that the duct thrust plays a key role in the enhancement of the power extraction, it does not allow for the evaluation of the flow field around the duct. For this reason, a semi-analytical model is also used to investigate the local and global features of the flow through a DWT. In comparison to the AMT, the proposed semi-analytical method can properly evaluate the performance of the device for each prescribed rotor load distribution and duct geometry. Moreover, in comparison to other linearised methods, this approach fully takes into account the wake rotation and divergence, and the mutual interaction between the turbine and the shroud. The analysis shows the opportunity to significantly increase the power output by enclosing the turbine in a duct and that the growth in the duct thrust has a beneficial effect onto the device performance. Finally, some insights on the changes occurring to the performance coefficients with the rotor thrust and the duct camber are obtained through a close inspection of the local features of the flow field.

RANS simulations of the stepped duct effect on the performance of ducted wind turbine

With the rise in oil price and population growth, renewable energies are assumed to be the main source of energies for the next generation. Wind as a natural, eco-friendly and renewable source of energy has been at the center of concentration for decades. Recently there has been some ideas regarding the self-regulating urban wind turbines. Researchers have shown that a proper enclosure increases the wind velocity and therefore more torques can be exerted on the rotors, therefore more power can be generated. These enclosures are light and cheap, therefore they are applicable and effective. In the present study, an enclosure was modified to increase the exerted torque with implementing a step at the outlet region of the enclosure. Comparison between the stepped and simple duct indicates the significance of the step role on the wind profile inside the enclosure. In order to find the proper position of the turbine inside the enclosure, three different locations for the turbine inside the enclosure were investigated and it was found that placing the turbine at inlet section of the enclosure has the most power coefficient. In the present case, implementing this simple step has increased the power coefficient by approximately 16%.

Performance analysis of open and ducted wind turbines

In this paper the analysis of the aerodynamic performance of ducted wind turbines is carried out by means of a nonlinear and semi-analytical actuator disk model. It returns the exact solution in an implicit formulation as superposition of ring vortices properly arranged along the duct surface and the wake region. In comparison with similar and previously developed models, the method can deal with ducts of general shape, wake rotation and rotors characterised by radially varying load distributions. Moreover, the nonlinear mutual interaction between the duct and the turbine, and the divergence of the slipstream, which is particularly relevant for heavily loaded rotors, are naturally accounted for. Present results clearly show that a properly ducted wind turbine can swallow a higher mass flow rate than an open turbine with the same rotor load. Consequently, the ducted turbine achieves a higher value of the extracted power. The paper also presents a detailed comparison between the aforementioned nonlinear and semi-analytical actuator disk method and the widely diffused CFD actuator disk method. The latter is based on the introduction of an actuator disk model in a CFD package describing the effects of the rotor through radial profiles of blade forces distributed over a disk surface. A set of reference numerical data, providing the inviscid axisymmetric velocity and pressure field distributions, are generated with controlled accuracy. Owing to an in-depth analysis of the error generated by the semi-analytical method and to the exactness of the solution in its implicit form, the collected data are well-suited for code-to-code validation of existing or newly developed computational methods.