Computational fluid dynamics study of the rear geometry influence on aerodynamic load coefficients of heliostats in stow position

Abstract

The study of heliostat load coefficients in stow position has become more extensive because of the importance of this scenario in the design process and cost estimation of an entire Concentrating Solar Thermal Power Tower plant. When in stow position, in the presence of high-velocity wind flow, heliostats behavior can be compared to an airfoil; as the air flows at different velocities over the upper and lower sections, significant pressure imbalances need to be considered. This paper presents a Large Eddy Simulation study of how four different geometries in the rear area of a squared heliostat at a horizontal inclination affect the magnitudes of the hinge moment (CMHy), drag (CFx), lift (CFz) and overturning (CMy) coefficients. Results show maximum differences of more than 128% for peak CFx when comparing type A and B geometries at the same 45° wind orientations. Also, for types A and B at β = 180°, peak CMy and CMHy presented differences of 47% and 36%, respectively, between heliostat models. Also, considering force's change in direction (i.e. lift vs downforce), a 219% maximum difference was observed for peak CFz between type A and type D models at β = 45°. The results show how the differences in shapes and size proportions between the front and rear heliostat sections affect the stow position's aerodynamic load coefficients (ALC). It was also observed that the ratio of the chord length to the maximum vertical distance from the rear mirror surface to the farthest point of structure geometry of the heliostat is directly correlated with ALC variations for analyzed heliostats.