Transient simulation of an atmospheric boundary layer flow past a heliostat using the Scale-Adaptive Simulation turbulence model

Abstract

Heliostat fields are exposed to changing climatic conditions as they are mostly erected in open environments where the wind naturally features a high unsteadiness at low altitude due to the ground effects. Much of the computational fluid dynamics (CFD) content in the open literature is focused on Reynolds–averaged-Navier–Stokes (RANS) simulations, which can only predict mean loads. This paper considers an isolated heliostat in worst-case orientation. The drag force is numerically modelled by means of a Scale-Resolving Simulation (SRS) in ANSYS v19. This paper firstly deals with two different methods that generate perturbations at the inlet boundary: the spectral synthesiser and the vortex method. In an empty domain, an atmospheric boundary layer (ABL) profile is modelled based on a wind tunnel experiment. Secondly, the wind tunnel test of a single heliostat model in upright orientation is replicated, aiming to model the mean and peak drag forces. Applicable for highly separated flows, the Scale-Adaptive Simulation (SAS) turbulence model is employed as it is computationally more affordable than a Detached Eddy Simulation (DES) approach. The latter would require a higher grid resolution and a reduced time step size. The SAS showed little but acceptable decay of the inlet profiles whilst achieving lateral homogeneity. The mean and root-mean-square error of the drag force signal showed a deviation with the experiment of 0.04% and 5.8%, respectively, whereas the error on the peak drag forces was around 18%, possibly mostly due to the under-prediction of the turbulent integral length scale at the model location.