Abstract
Wind energy is one of the main alternative energy sources and is present in various forms, from large offshore wind turbine installations, to small, privately used, small horizontal wind turbines (SHWT). Optimization of the turbine blades, and eventually of their efficiency, is of great importance, especially for SHWT. SHWT are exposed to a turbulent inflow, where 3D flow effects are dominant due to the relatively small length of the wind turbine blades. At the edge of the blade, tip vortices are generated, inducing high drag and significantly reducing the lift and torque generated near the blade tip. In order to convert this energy to useful lift, a winglet can be applied at the tip of the blade by acting in a comparable manner to a blade span increase. In the current paper the effect of five winglet modifications on the overall generated power of a SHWT is presented. More specifically, four distinct winglet cant angles are selected for this optimization procedure. Parameters such as winglet height, sweep of the winglet, toe angle and twist angle are held constant, in order to highlight the effect of the different cant angles. The sole exception is that one of aforementioned designs is further modified with a sweep angle of 20°, in order to assess the possible change in the aerodynamic behavior. The CFD computations for the evaluation of the proposed modifications use a rotating frame, with one of the three blades of the SHWT. The addition of the winglet alters significantly the flow pattern over the wing tip. As a result, the aerodynamic performance and the torque generation are improved from 1.5 % to almost 11 %, underlining the potential of further optimizing blades of SHWT.
