Flow Behaviour and Aerodynamic Loading on a Stand-Alone Heliostat: Wind Incidence Effect

Abstract

Heliostats represent a significant proportion of the cost of central tower concentrating solar power systems; hence, there is a need to reduce the cost of these. One of the challenges faced in doing this is to ensure that any new design is still able to cope with the loads imposed upon it, particularly the aerodynamic loads. Numerous studies have reported the aerodynamic loadings encountered by heliostats for multiple operational conditions. However, these studies only extracted and reported these values without relating their findings of the variation in wind loads with heliostat orientation to the airflow characteristics around the structure. Besides, there is a marked absence of studies that rigorously explore in any detail the wind incidence effect and the impact that has on the aerodynamic behaviour of a heliostat. In this study, computational fluid dynamics was utilized to investigate the effect of wind incidence angles on a heliostat operating at varying tilt angles, to better characterize the aerodynamic loading of these structures and to relate these loads to the wind flow field around the heliostat. The results, validated against wind tunnel test data, showed that the tilt and wind incidence angle had a significant influence on the aerodynamic coefficients that varied strongly across the multiple operational conditions investigated. Moreover, the airflow field around the heliostat structure showed markedly different behaviour characteristics with the change in wind incidence angle. Considering a full range of tilt angles between 90° and − 90°, and incidence angles ranging from 0° to 90° with an angular resolution of 11.25°, the work delivers a fuller characterization of the lift, drag, base overturning moment and hinge moment coefficients than previously available. In achieving this, it delivers a generalized correlation for each of the coefficients based on the heliostat’s orientation with respect to the wind. When paired with existing gust loading relationships, these formulations provide a useful analytical tool to assess structural loads on a heliostat.