Heliostat wind loads in the atmospheric boundary layer (ABL): Reconciling field measurements with wind tunnel experiments

This paper investigates similarity effects of atmospheric boundary layer (ABL) turbulence in full-scale field measurements and wind tunnel experiments on the aerodynamic wind loads on a single heliostat. Two experimental studies were conducted at the University of Adelaide: (1) field measurements of ABL wind turbulence and six-axis load cell measurements on an instrumented heliostat in open farmland at the Atmospheric Boundary Layer Research Facility (ABLRF), and (2) wind tunnel (WT) testing of six-axis load cell measurements on a 1:6 scale model heliostat in a simulated ABL. It was found that mean and peak wind load coefficients at the ABLRF during a high-wind period with steady wind direction showed similar variations with elevation angle as WT study. Load coefficients at ABLRF showed only a small variation with changes in mean wind speed and the streamwise component of turbulence intensity, however, drag and lift force coefficients varied due to the anisotropic turbulence intensities, spectra and integral length scales of longitudinal and vertical wind components at ABLRF that deviated from Engineering Sciences Data Unit (ESDU) and WT data at heights below 5 m. Load coefficient distributions at ABLRF showed increased skewness and non-Gaussian behaviour compared to the corresponding WT distributions. The results of this work found that wind tunnel experiments overestimate drag force coefficients and underestimate lift force coefficients compared to ABLRF field measurement. This is critical for verification of aerodynamic wind load coefficients in wind tunnel experiments and the sensitivity of single heliostat wind loads to ABL turbulence characteristics.