Microtabs for the mitigation of the tower shadow effect

As the structural limits for the conventional horizontal-axis wind turbine are being reached, innovative concepts are needed to ensure increased reliability and reduced costs. One option is limiting the fatigue to which a rotor is subjected. This study, therefore, intends to experimentally investigate the tower shadow effect for a deeper understanding of the aerodynamic fluctuations, and to study the capability of a lower surface microtab to mitigate such fluctuations. For this, aerodynamic load variations caused by the presence of the tower on the rotor blades were reproduced and studied in the wind tunnel using a setup that mimics the interaction between the tower and the blade. Anemometers and flow visualisation techniques were used to explore the influence of the tower on the surrounding flow field. Real-time measurements show that the alterations in the lift force are mainly caused by the alterations in the flow angle and have proven that a lower surface microtab can partially mitigate aerodynamic load variations in the case of an upwind rotor blade. Experimental results are validated using a tower shadow model that is based on potential flow theory. The tower shadow model shows a reduction in 3p power oscillations by a factor of 2.