AuthorSteven Tran, David Corson, Onkar Sahni
TitleSynthetic Jet based Active Flow Control of Dynamic Stall Phenomenon on Wind Turbines Under Yaw Misalignment
JournalAIAA Paper 2014-0871
AbstractOne of the largest contributors to the structural failure of wind turbines is the unsteady aerodynamic loading experienced by the blades. This can arise due to yaw misalignment, wind shear, gusting or a combination of these conditions. Under these conditions, cyclic blade loading occurs and dynamic stall phenomenon is possible which in-turn results in hysteresis and causes vibrations in turbine components. Therefore, it is important to mitigate, or even fully suppress, dynamic stall. In this paper we use numerical simulations to study synthetic-jet based active flow control to mitigate dynamic stall. The goal is to achieve fast-time response control with actuators that require low energy input and are physically compact. We focus on the NREL Phase VI turbine with the S809 airfoil shape. The baseline con figuration (without synthetic jets) is modeled at below rated (7 m/s), rated (10 m/s), and above rated (15 m/s) wind speeds and at a yaw angle of 30. It is found that the unsteady loading due to yaw misalignment can cause power fluctuations of up to 9kW or 135% for each blade during one blade revolution. Next we study active flow control on a pitching S809 airfoil with a synthetic-jet actuator, where two wind conditions are considered that correspond to the yaw angle of 30 for two wind speeds of 10 and 15 m/s at blade span of 60% and 80%, respectively. The jet is placed at 5% chord location (i.e., x/c=0.05) and is activated at a non-dimensional frequency of 5. Synthetic-jet based control is shown to significantly reduce the flow separation near the leading edge and thus, reduce the hysteresis by up to 73% at the rated wind speed.
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DOI Link10.2514/6.2014-0871