[Ground effects of an aerofoil using CFD]

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Table of Contents

1. Introduction3

1.1 Background to the Project3

1.2 Project Objectives5

1.3 Overview of This Report6

1.4 Methodology6

References10

1. Introduction

1.1 Background to the Project

The demand of energy production from renewable energies such as wind turbines has increased a lot during the last 25 years (Bourdet et. al. 2012, pp. 451-476). Thus, the small wind turbines offered in the early days of the wind energy industry with a power capacity of 20-30 kW have been improved to obtain wind turbines giving a capacity of 3-5 MW, or even 7.5 MW. It is well known that this increase in nominal power given, related with an increase of the size of the turbine, involves an increase of the loads on the wind turbine components(Genc¸, 2010, pp.2155-2164). The wind energy industry is working hard on research for solutions to support these loads while maintaining this high annual energy production achieved. The option which is being investigated by some companies and research centers are the flatback airfoils. The trailing edge of these airfoils is opened towards pressure and/or suction side in order to modify the airfoil properties(Kontis, 2012, pp. 249-251).

These blunt trailing edge airfoils basically increase both the sectional area and the sectional moment of inertia, thus reducing weight and optimizing structural material placement and blade strength. Thus, they are a very good option to be situated at the root of the blade (where the thickest sections are found) because it is well known that inboard sections have to be designed to provide more structural performance, while outboard sections are thought to give better aerodynamic characteristics(Da Ronch, et. al. 2011, pp. 100-105).

Furthermore, thick flatback airfoils are supposed to be less sensitive to surface soiling. Nevertheless, due to the vortex formation at the trailing edge they generate more drag and low frequency noise with higher intensity (Liu, 2010, pp. 405-423). This is another beneficial reason for these flatback airfoils at the inner part of the blade, where the lower relative velocities are found. Studies have been made to decrease this negative effect, including modifications like addition of a splitter plate (with both serrated and not serrated shape at the end), which can reduce the overall drag by 50 % and create less intensity noise with higher frequencies(Djayapertapa, 2012, pp. 413-443).

In order to know about the aerodynamic performance of these airfoils wind tunnel experiments or Computational Fluid Dynamics (CFD) have to be done. Sandia Laboratories from California, shows the results for wind tunnel experiments on thick flatback airfoils, the airfoil FB-3500-0050 and the modifications made to its trailing edge (by opening its trailing edge the same percentage towards both pressure and suction side). CFD has also been used by Sandia Laboratories in order to study these airfoils (Ansari, 2009, pp. 61-83). The airfoil DU-97-W-300 is studied using CFD (Roohani, 2008, pp. 631-636). Another MSc thesis has been done in order to study with CFD the performance of the airfoils FB-3500-0050 and DU-97-W-300 and the modifications made to their trailing edges (Jonathan, 2012, ...