1,720,976 research outputs found
Effects of yawed inflow on the aerodynamic and aeroacoustic performance of ducted wind turbines
Get PDFDucted 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 aero-acoustic 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
Ducted wind turbines in yawed flow: A numerical study
Get PDFDucted 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 angle
Experimental Study Of Flow Field Of An Aerofoil Shaped Diffuser With A Porous Screen Simulating The Rotor
No full textThis study presents an experimental investigation on a diffuser augmented wind turbine (DAWT). A screen mesh is used to simulate the energy extraction mechanisms of a wind turbine in experiment. Different screen porosities corresponding to different turbine loading coefficients are tested. Measurements of the axial force and of the velocity distribution in radial direction are reported. The general purpose is to highlight the dependency between the diffuser and the screen, and to compare the radial velocity distributions in the diffuser between unloaded and loaded conditions. It is shown that the thrust on an unshrouded screen is lower than on a shrouded screen, under the same inflow condition. Moreover, the thrust on the diffuser largely depends on the screen loading. For the present configuration, the thrust on the screen with high loading coefficient contributes for more than 70% of the total thrust on the DAWT. Smoke visualizations and radial velocity profiles reveal that the high loading screen induces flow separation on the outer surface of the diffuser, justifying the results of the thrust measurements. It is also inferred that the flow separation leads to loss of thrust and has a great effect on the total pressure drag. It should be emphasized that the experimental results indicate that the flow field around the diffuser is strongly affected by the choice of screen porosity, that is, turbine loading. And that, the thrust coefficient of the diffuser does not show a linear dependence on the thrust coefficient of the screen. The axial momentum theory, therefore, is not a solid predictor for DAWT performance with high loaded screens
Computational Study Of Diffuser Augmented Wind Turbine Using Actuator Disc Force Method
No full textIn this paper, a computational approach, based on the solution of Reynolds-averaged-Navier–Stokes (RANS) equations, to describe the flow within and around a diffuser augmented wind turbine (DAWT) is reported. In order to reduce the computational cost, the turbine is modeled as an actuator disc (AD) that imposes a resistance to the passage of the flow. The effect of the AD is modeled applying two body forces, upstream and downstream of the AD, such that they impose a desired pressure jump. Comparison with experiments carried out in similar conditions shows a good agreement suggesting that the adopted methodology is able to carefully reproduce real flow features
Experimental investigation on the effect of the duct geometrical parameters on the performance of a ducted wind turbine
No full textThis paper reports an experimental investigation on the effect of the duct geometry on the aerodynamic performance of an aerofoil shaped ducted wind turbine (DWT). The tested two-dimensional model is composed of an aerofoil equipped with pressure taps and a uniform porous screen. The experimental setup is based on the assumption that the duct flow is axisymmetric and the rotor can be simulated as an actuator disc. Firstly, different tip clearances between the screen and the aerofoil are tested to point out the influence of this parameter on the DWT performance in terms of aerofoil pressure distribution, aerofoil lift and flow field features at the duct exit area. Then, the combined effect of tip clearance, of the angle of attack and of the screen position along the aerofoil chord is evaluated through a Design of Experiments (DoE) based approach. The analysis shows that, among the analysed range of design factor variation, increasing angle of attack and the tip clearance leads to a beneficial effect on the lift and back-pressure coefficients, while they show a poor dependence upon the screen axial position. Finally, the configuration characterized by the maximum value of all three main factors (15 degree of angle of attack, 5% of tip clearance and 30% backward to the nozzle plane), has the best values of lift coefficient and back-pressure coefficient.Wind Energ
Effects of gurney flap on the performance of diffuser augmented wind turbines
No full textIn this paper, a numerical investigation on the effect of gurney flap (GF) on the performance of a diffuser augmented wind turbine (DAWT) is presented. The flow-field around the DAWT is obtained by solving the Reynolds-averaged-Navier-Stokes (RANS) equations. The turbine is modelled as an uniformly loaded actuator disc (AD) that imposes a resistance to the passage of the flow. Comparison of the numerical results with experimental measurements in similar conditions shows that the numerical approach used satisfactorily reproduces the mean flow field. GF heights equal to 2% and 4% of the diffuser chord length were investigated. Results show that separation induced by GF creates a low pressure region at the diffuser exit, that increases the mass flow through the diffuser and the power coefficient of the DAWT
How does the presence of a body affect the performance of an actuator disk ?
No full textThe article seeks to unify the treatment of conservative force interactions between axi-symmetric bodies and actuators in inviscid flow. Applications include the study of hub interference, diffuser augmented wind turbines and boundary layer ingestion propeller configurations. The conservation equations are integrated over infinitesimal streamtubes to obtain an exact momentum model contemplating the interaction between an actuator and a nearby body. No assumptions on the shape or topology of the body are made besides (axi)symmetry. Laws are derived for the thrust coefficient, power coefficient and propulsive efficiency. The proposed methodology is articulated with previous efforts and validated against the numerical predictions of a planar vorticity equation solver. Very good agreement is obtained between the analytical and numerical methods
Turby - sustainable urban wind power from the roof top
No full textIf current trends are anything to go by, in future we will no longer produce all our electricity in large, central power stations. Small-scale local electricity generation will gain in importance. Sander Mertens, a post-doctoral student at TU Delft, developed the aerodynamic design of a wind turbine which is specifically suitable for built-up areas. Compact, mobile, low-noise, and vibration-free, it is the ideal alternative for use on top of high-rise office blocks, where wind speeds can easily reach twenty percent more than with the same height away from buildings. The electricity can be fed straight into the buildings power system, saving on energy transport costs and losses, and producing high feed-in yields. Prototypes have already been installed on the town hall in The Hague (designed by Richard Meier), on an apartment block in Tilburg, on an office block in Breda, and on top of the Delft ChemTech faculty building. Interest has been generated in London and Leicester in the UK, New Mexico and New York in the USA, and in France and Canada
- …
