Site characterization through the use of computational fluid dynamics

Abstract

Numerical simulations of airflow over various potential sites for extremely large telescopes have been performed. Information such as wind speed, turbulence levels (fluctuating velocity RMS), wake lengths, boundary (ground) layer thickness and the effects of topographically induced turbulence on seeing can be retrieved, thus providing an essential evaluation tool in the site selection process. We present a sample set of simulations carried out over possible site locations for a 20-30m-telescope project. Simulations at several different sites located in Chile were performed in terms of wind speed levels and the effects of the local topographic features on the flow in the summit region, namely turbulent intensity and boundary layer thickness, under the prevailing wind conditions. Results indicate that the turbulent boundary layer thickness, defined as the region of considerable turbulent intensity levels, ranges from 10m to ~400m, depending on peak location and wind direction, for summit wind speeds varying between 4 and 12 m/s.