Session: 18-02 HelioCon Windload

Paper Number: 141897

141897 - Effects of Atmospheric Boundary Layer Turbulence on Single Heliostat Wind Load Coefficients: Comparison of Field Measurements With Wind Tunnel Experiments 

Abstract: 

This paper investigates similarity effects of atmospheric boundary layer (ABL) turbulence in full-scale field measurements and wind tunnel (WT) 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 testing of six-axis load cell measurements on a 1:6 scale model heliostat in a simulated part-depth ABL.

It was found that mean and peak wind load coefficients at the ABLRF during a during a 3-hour period with steady wind direction from the south-west on 13 December 2022 showed similar variations with elevation angle as the WT study. Load coefficients at constant elevation angles of between 0° and 90° in 15° intervals during 10-minute periods at ABLRF showed only a small variation with changes in mean wind speed and the streamwise component of turbulence intensity, however, lift force and hinge moment coefficients showed a significant variation with the vertical turbulence component due to instabilities in the unstable ABL during the afternoon-evening transition. It was found that a fitted Gaussian distribution at ABLRF underestimates the peak drag force by 5% and the peak azimuth moment by 12% compared with the peak value of a fitted Weibull distribution. Distributions of drag and lift forces, and hinge and azimuth moments at ABLRF showed increased skewness and non-Gaussian behaviour due to increasing anisotropy of turbulence length scales compared to the corresponding WT distributions in a part-depth ABL. The size of integral turbulence length scales at the elevation axis height relative to the heliostat chord length in agreement with wind tunnel studies (Emes et al. 2017; Pfahl 2018; Emes et al. 2019, Jafari et al. 2019) to have a significant influence on peak wind load coefficients in stow and maximum operating positions. The ratio of integral length scales of the streamwise and vertical components at the heliostat elevation axis height (1.6 m) to heliostat chord length, varied from 14-50 and 0.5-3.6 during the ABLRF measurement period on 13 December 2022. In comparison, these ratios were approximately 1.33 and 0.53 for the 1:6 scale heliostat model in the wind tunnel part-depth ABL (Marano et al. 2024).

Peak frequencies of the fluctuating load components measured by six=axis load cell measurements increased with increasing elevation angle from 1° to 86° in the range of 5-8 Hz, except for the lift force in the range of 16-26 Hz. The results of this work show the importance of field measurements for verification of aerodynamic wind load coefficients in wind tunnel studies and the sensitivity of single heliostat wind loads to ABL turbulence characteristics and atmospheric stability. Further study of wind loads on a structurally representative heliostat at different azimuth angles and their sensitivity to ABL turbulence characteristics would be useful to refine and evaluate load-turbulence correlations developed in WT experiments and their impact on cost and operating performance of heliostats in a field environment.

Presenting Author: Matthew Emes The University of Adelaide

Presenting Author Biography: Dr Matthew Emes is a Postdoctoral Research Fellow in the School of Electrical and Mechanical Engineering at the University of Adelaide. His research interests are in experimental fluid mechanics, aerodynamics and wind engineering of renewable technologies. He has expertise in wind tunnel experiments and field measurements of atmospheric boundary layer turbulence parameters and their influence on wind load design of single heliostats and heliostat arrays. He leads the wind load subtopic within Task 7 Field Deployment in HelioCon working on measurement, characterization and prediction of wind loads on heliostats to develop wind site characterization and heliostat wind load design guidelines with the aim to reduce cost and increase performance of heliostat fields.

Authors:

Matthew Emes The University of Adelaide
Matthew Marano The University of Adelaide
Maziar Arjomandi The University of Adelaide