Researchers in Japan use Aeroprobe Probes to Explore the Unsteady Aerodynamics of a Wind Turbine

Researchers at Mie University in Japan instrumented the blades of a horizontal-axis wind turbine to explore their unsteady aerodynamics. The rotor diameter was 10 m and the hub height above the ground was 13.3 m. A sonic anemometer and vane-cup anemometers were mounted on three masts upstream of the turbine as shown in the figure below to record the properties of the on-coming wind. Depending on the wind direction and magnitude, the blades of a wind turbine may go in and out of stall during one revolution. In fact, the extent of stall varies in the spanwise direction of each blade.

Extensive distributions of pressure gauges and strain gauges were employed to monitor and record the structural moments and the relationship of the aerodynamic variations to the oscillation frequencies of the root bending moments.

The instantaneous apparent angles of attack at different sections along the instrumented blade were measured by Aeroprobe custom-built seven-hole probes spaced as shown in the figure below. These probes recorded the instantaneous wind speed and direction in the blade reference frame. The blade angle of attack and therefore stall conditions are defined in this frame of reference.

The researchers found that for operation away of stalled conditions, the frequency of the blade root bending moment is equal to the rotational frequency. But if the blades stall, the dominant frequency is the frequency of the first mode of oscillation of the blade.