Characterization of the SUMO Turbulence Measurement System for Wind Turbine Wake Assessment

Abstract The remotely piloted aircraft system (RPAS) SUMO (Small Unmanned Meteorological Observer) has been equipped with a miniaturized 5-hole probe sensor system for measurement of the 3-dimensional flow vector with a temporal resolution of 100 Hz. Due to its’ weight and size this system is particularly well suited for operations in the vicinity of wind turbines. To qualify for full scale measurements in turbine wakes the system has been characterized by several laboratory and field tests described in this study. A wind tunnel test against a hot-wire anemometer shows the capability of the 5-hole probe to react to turbulence in the same manner as the hot-wire system. The resulting spectra from the two platforms show in general good agreement for both laminar and turbulent flows. The 5-hole probe system is able to resolve turbulence up to frequencies around 20 − 30 Hz when using a tubing length of 15 cm between the probe and the pressure transducers. In addition, an environmental parallel test against to two sonic anemometers mounted on the roof-top of a car was performed at Bergen airport Flesland. Despite several issues with the self-made and low-cost experimental setup, important system characteristics could be tested and verified. In particular the velocity spectral components of the sonic anemometer system and the 5-hole probe are in close resemblance to each other. This is at least a strong indication that the 5-hole probe is suitable for atmospheric turbulence measurements onboard the RPAS SUMO platform.