Wind tunnel test for the preliminary design of the European Solar Telescope

The European Solar Telescope (EST) is a 4.2-m solar telescope, based on an aplanatic Gregorian configuration with an alt-azimuthal mount. EST has an open configuration for observations without dome to improve the local seeing around the telescope mount and the main optical elements, enhancing the natural air flushing through the structure. This approach minimizes the active thermal control and reduces the telescope´s installation and operating costs. In contrast, the wind will be an extra load that requires a stiff telescope structure, as well as an advanced adaptive optics and control system. This contribution presents the comprehensive wind tunnel testing campaign carried out for the preliminary design of the Telescope Structure, Enclosure and Pier. The objective of these tests is to compare the results obtained from Computational Fluid Dynamics (CFD) analysis and to consolidate the results obtained from the Finite Elements (FE) and the end-to-end control analysis. For this purpose, three models were built. The first one is a topography model with a 2 km radius area, the second one is a detailed proximity model including neighboring telescopes and the last one is a detailed telescope model including the axes and main optical elements. The results of the tests were compared with FE and CFD analysis, observing differences lower than 15% in representative indicators. This allowed for an empirical correlation of the models. Additionally, the wind load contribution to the pointing and tracking error budgets were replicated with the correlated models, bringing compliant results with the performance requirements.