A Novel Approach for Computational Fluid Dynamics Analysis of Mean Wind Loads on Heliostats

A computational fluid dynamics study about the aerodynamic loads over a heliostat due to an atmospheric boundary layer flow using a modified k–ɛ turbulence model is presented. A new formulation is used, in which the model quantities vary with the velocity field. Modified wall functions for roughness were used at the bottom of the computational domain to achieve horizontal homogeneity of the airflow. Good horizontal homogeneity for the streamwise and spanwise velocity and turbulence intensity profiles were found. The incident profiles were compared with the inlet ones. The average percentage differences were 0.22% for velocity and 0.43% for turbulent intensity. Good agreement was found between the numerical data and theoretical values of the streamwise and spanwise shear stress at the bottom of the domain. The aerodynamic coefficients of the heliostat at different elevation angles were obtained, and a good agreement was found between the numerical data concerning the wind tunnel experimental values. An average percentage difference of 3.1% was found for drag, 6.5% for lift, and 6.0% for overturning. A significant improvement was obtained by using this new formulation with respect to a non-modified k–ɛ turbulence model. The average differences of the aerodynamic coefficients were 6.6% for drag, 12.4% for lift, and 10.1% for overturning. The velocity, turbulent kinetic energy, and pressure fields at different elevation angles were analyzed. It was found that at an elevation of 60 deg, the stagnation point of the flow occurs at the superior edge of the heliostat, causing the maximum lift force over the structure.