WIND TURBINE

The blade for a 10kW horizontal axis wind turbine

The blade for a 10kW horizontal axis wind turbine

Introduction

The general goal in optimizing the aerodynamic execution of wind turbines is to increase power extract ion with a minimal increase to the overall cost of the system. For this motive, utility scale wind turbines are modified for the best results at least cost, since they are equipped with large, very expensive blades. It is believed, however, that the idea of aerodynamic optimization could play a larger role in the competence of small wind turbines, as these tremendous costs cannot be applied on horizontal-axis wind turbines (HAWT's) more suited for smaller utilities such as home use. The goal of this study is to optimize the functioning of small HAWT's by examining the effect of blade movement on turbines with more than three blades.

Discussion

The optimization of a wind turbine's aerodynamic execution relies on many factors and variables, including blade number (B); rotor solidity (s), the fraction of blade area to swept area; blade movement (ß), the angle between the chord line and the plane of rotation; and tilted point's momentum fraction (?), the fraction of peripheral tilted point's momentum to wind momentum. Aerodynamic execution of small HAWT's has been an active research topic over the past few years (Humiston, and Visser, 2003).

In the turf of renewable energy the ADAG group has performed the study and optimization of horizontal axis wind-turbines. Specifically, designs of airfoils for wind-turbine effectiveness optimization have been carried out. A specific edge has been the implementation of CAD/CAM technologies for blade design as well as manufacturing.

Other research activities concern the blade structural and aeroelastic analysis. Initial numerical studies investigated the implications of solidity and blade number and have since been examined experimentally in the wind tunnel and at a full-scale level at the University Wind Turbine Examination Area, located at the Potsdam Airport. The full scale experiment, comparing a standard three-blade Bergey XL.1 with an experimental trial model six-blade turbine, shows an increase in power extraction at lower wind momentums for increased blade number and solidity. The trial model has also shown that it's higher torque results in lowered operational tilted point's momentum fraction, a decreased tilted point's momentum fraction at maximum power coefficient (Cp), the fraction of extracted power to the power in the wind, and reduced cut-in wind momentums (Duquette, and Visser, 2003).

The impact of blade movement angle is a critical parameter for the aerodynamic optimization of untwisted blades. The numerical studies performed earlier for multi-bladed turbines include this parameter, as well, indicating a turbine with a 10° blade movement angle resulting in a 20% higher Cp than one at 20°. They also suggest an increased tilted point's momentum fraction at maximum Cp for a reduced blade movement angle, greatly affecting the tilted point's momentum fraction range of operation.

This thesis examines the effect of blade movement on a six-bladed turbine in an effort to optimize its aerodynamic execution so as to extract the highest power and force production ...