A Characterization of Vertical Axis Wind Turbines
Vertical axis wind turbines (VAWT) have a number of advantages over the horizontal axis wind turbines (HAWT), however the performance is a little smaller, so that researches for their development should be continued for the implementation of these turbines in urban environment for electrical energy generation. This paper provides an overview of characterization of the VAWT, through a literature review, making comparisons with the HAWT and highlighting the advantages and disadvantages of this type of turbines. The paper also defines and compares the main exist types of VAWT for application in urban environment, so that aims to be a first step towards development of a VAWT research. Finally, this paper features how the aerodynamic optimization of a VAWT can be obtained, defining the experimental and the computational numerical analysis, by the relationship between them.
Development of low-noise drag-type vertical wind turbines
In this study, the aerodynamic noise characteristics of Savonius wind turbines were investigated using hybrid computational aero-acoustics techniques, and low-noise designs were proposed based on the understanding of the noise generation mechanism. First, the flow field around the turbine was analyzed in detail by solving three-dimensional unsteady incompressible Reynolds-averaged Navier–Stokes equations using computational fluid dynamics techniques. Then, the aerodynamic noise radiating from the wind turbine was predicted using the Ffowcs Williams and Hawkings equation with the obtained flow field information. Two distinct harmonic noise components—the blade passing frequency (BPF) and harmonics with a fundamental frequency that is much higher than the BPF—were identified in the predicted noise spectrum. The origin of the higher harmonic components was found to be related to vortex shedding from the rotating turbine. Based on this finding, the proposed low-noise design for Savonius wind turbines uses S-shaped blades. S-shaped blades were found to reduce the noise levels of Savonius wind turbines by up to 2.7 dB.
Modeling Strategy and Numerical Validation for a Darrieus Vertical Axis Micro-Wind Turbine
This paper presents a model for the evaluation of optimal spatial grid node distribution in the CFD analysis of a Darrieus vertical axis micro wind turbine, by analyzing the trends over a 360° rotation of some indicators of near-blade mesh quality. To this purpose, a complete validation campaign has been conducted through a systematic comparison of numerical simulations with wind tunnel experimental data. Both two-dimensional and three-dimensional grids, characterized by average y+ values of 30 and 1, have been tested by applying some statistical techniques as a guidance in selecting the appropriate grid configuration and corresponding turbulence model. Finally, the tip downstream recirculation zone due to the finite blade extension and the influence of spokes have been analyzed, achieving a numerical quantification of the influence of induced drag and spokes drag on overall rotor performance.Copyright © 2010 by ASME