112,093 research outputs found
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
Multi-element ducts for ducted wind turbines: A numerical study
No full textMulti-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.</p
Effects of yawed inflow on the aerodynamic and aeroacoustic performance of ducted wind turbines
No full textDucted 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
No full textDucted 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
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
author-bios-SRD-19-0063.R1 – Supplemental material for The Network Structure of Police Misconduct
No full textSupplemental material, author-bios-SRD-19-0063.R1 for The Network Structure of Police Misconduct by George Wood, Daria Roithmayr and Andrew V. Papachristos in Socius</p
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
