Aerodynamic optimisation of small scale horizontal axis wind turbine blades

The power generation by a Horizontal Axis Wind Turbine (HAWT) is considered to be at the forefront of technology due to its reliability and cost effectiveness. However the efficiency of wind turbines is not at the desired level due to inefficient extraction of power from the wind by the turbine blades. The turbine blades experience an undesirable phenomenon at the tip of the blade known as vortex due to the pressure difference on the surface of the blade. The presence of the vortex impairs the performance of the turbine blades as it reduces the lift to drag ratio. Hence, the primary objective of this study is to understand and augment the aerodynamic performance of small scale HAWT for the application in built-up areas. <br>The research was undertaken using both experimental investigation in wind tunnel and computational fluid dynamics (CFD) modelling. Three sets of blade configuration were used in this study. Each set of wind turbine blade is distinguished by its unique blade tip design. A straight tapered blade with no winglet attached, backward facing winglet blade and a forward facing winglet blade were designed and manufactured. A series of tests were conducted at RMIT Industrial Wind Tunnel where the aerodynamic characteristics of the wind turbine blades (lift, drag and side force) and the power generation capabilities (<em>C_P</em>) were investigated. Additionally, the influence of the interference drag caused by the presence of the nacelle was also examined. <br>The aerodynamic behaviour of the turbine was undertaken at a range of wind speeds and yaw angles. CFD modelling also employed to determine and understand the power output potential and flow behaviour of the wind turbine. <br>The aerodynamic behaviour of each wind turbine blade tip configuration significantly differed. The forward facing winglet blade produced a greater lift coefficient <em>C_L</em> at 0° yaw angle in comparison to the straight blade (with no winglets) and the backward facing winglet blade. The findings show that the forward facing winglet increases the lift to drag ratio (L/D) of 26% compared to the straight blade. However, the backward facing winglet blade decreases the L/D ratio of 27%. The turbine power coefficient has increased notably for the forward facing winglet compared the baseline blade (straight blade). A significant reduction in power coefficient was noted for the backward facing winglet.<br>Positioning the winglet at the suction side of the blade effectively reduces the span wise airflow at the tip thereby improves the aerodynamic performance. It was also found that extending the gap between the wind turbine hub and the nacelle increases the power output. <br>