This conference paper was submitted for presentation at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

The European Solar Telescope (EST) is a next generation 4-m class solar telescope that will be built at the Observatorio del Roque de los Muchachos (ORM). The performance of an optical telescope is evaluated by its seeing, which refers to the image degradation caused by turbulent fluctuations in the air's refractive index as light travels through the optical path. This phenomenon arises from various sources, including atmospheric turbulence, environmental and local effects. Atmospheric turbulence is largely determined by the site location and the ORM is renowned for its excellent atmospheric conditions for astronomical observation. The EST design aims to minimize environmental local turbulence effects caused primarily by the thermal ground layer. This is achieved by placing the optical elements as high as possible from the ground and using an open-air configuration that promotes natural ventilation. The local fluctuations in the air refractive index in the surrounding of the telescope are produced by a combination of thermal and mechanical turbulence that depends on the size and shape of the design. To evaluate the local effects, detailed Finite Element Thermal and Computational Fluid Dynamics (CFD) models were developed. These models accounted for the topography, telescope structure, pier, enclosure and nearby telescopes within the observatory. Transient thermal analysis calculates superficial temperatures which are subsequently used by the CFD model to compute the air temperature distribution and its refractive index. A series of transient CFD analyses is conducted to analyze the impact of environmental conditions, including wind speed, wind direction and telescope orientations, on different design alternatives. These simulations provide further insights into the spatial distributions of air temperature and refractive index fluctuations inside the optical path. The results are postprocessed to derive aero-optical metrics, allowing to estimate the telescope performance. The study highlights how design choices influence aero-optical turbulence and provides feedback for optimizing the EST'™s design. The results contribute to the telescope'™s error budget by quantifying local turbulence effects and ensuring that the aerodynamic design supports its optical performance goals.