Calibration Procedure and Accuracy of Wind and Turbulence Measurements with Five-Hole Probes on Fixed-Wing Unmanned Aircraft in the Atmospheric Boundary Layer and Wind Turbine Wakes

• Published in: Atmosphere 2019-03, Vol.10 (3), p.124
• Main Authors: Rautenberg, Alexander, Allgeier, Jonas, Jung, Saskia, Bange, Jens
• Format: Article
• Language: English
• Subjects: 3D wind vector measurement; Accuracy; Aerodynamics; Aircraft; Airspeed; airspeed variations; Atmospheric boundary layer; Boundary layers; Calibration; calibration of multi-hole probes; Coordinate transformations; Fixed wings; flow probes; Fluid flow; Inertial navigation; Influence; Interpolation; Kinetic energy; Mathematical analysis; Measurement; Measurement techniques; Navigation; Navigation systems; Polynomials; Reynolds number; Statistical analysis; Statistical methods; Statistics; tip vortex; Turbine engines; Turbines; Turbulence; Turbulence measurement; turbulence measurements; Turbulent kinetic energy; unmanned aerial systems (UAS); Unmanned aerial vehicles; unmanned aerial vehicles (UAV); Unmanned aircraft; Variation; Velocity; Wakes; Wind measurement; Wind power; wind turbine wake; Wind turbines; Wing tip vortices; Wings
• ISSN: 2073-4433; 2073-4433
• DOI: 10.3390/atmos10030124

For research in the atmospheric boundary layer and in the vicinity of wind turbines, the turbulent 3D wind vector can be measured from fixed-wing unmanned aerial systems (UAS) with a five-hole probe and an inertial navigation system. Since non-zero vertical wind and varying horizontal wind causes variations in the airspeed of the UAS, and since it is desirable to sample with a flexible cruising airspeed to match a broad range of operational requirements, the influence of airspeed variations on mean values and turbulence statistics is investigated. Three calibrations of the five-hole probe at three different airspeeds are applied to the data of three flight experiments. Mean values and statistical moments of second order, calculated from horizontal straight level flights are compared between flights in a stably stratified polar boundary layer and flights over complex terrain in high turbulence. Mean values are robust against airspeed variations, but the turbulent kinetic energy, variances and especially covariances, and the integral length scale are strongly influenced. Furthermore, a transect through the wake of a wind turbine and a tip vortex is analyzed, showing the instantaneous influence of the intense variations of the airspeed on the measurement of the turbulent 3D wind vector. For turbulence statistics, flux calculations, and quantitative analysis of turbine wake characteristics, an independent measurement of the true airspeed with a pitot tube and the interpolation of calibration polynomials at different Reynolds numbers of the probe’s tip onto the Reynolds number during the measurement, reducing the uncertainty significantly.