Direct Mechanical Power Measurement of a Miniature Wind Turbine

Miniature wind turbines are used in the study of wind farms and their wake interactions in wind tunnel experiments. It is often desirable in such experiments to measure the power that is mechanically extracted from the flow by the wind turbine. Typically, the power is measured indirectly via the electrical power generated by a motor in the hub of the turbine. However, this is not a perfect substitute due to electrical losses obfuscating the relationship between the fluid dynamics and the mechanical power. Here a new design for directly measuring the mechanical power of a miniature wind turbine is proposed. Strain gauges are applied to webbed sections of spring steel at the base of the tower, one parallel and one perpendicular to the flow, to measure the torque and drag. Mechanical power is then obtained by multiplying the measured torque by the rotor's angular velocity. Existing designs have employed strain gauges but face problems such as bearing friction. This new design eliminates the need for bearings and has the potential to be used with slimmer nacelle designs. The turbine performance is characterized using the directly measured mechanical power and results are supported through calibration of the electrical power and measuring the velocity deficit in the wake.