Correlation of CFD predictions and wind tunnel measurements of mean and unsteady wind loads on a large optical telescope

Complementary studies, involving computational fluid dynamics (CFD) analyses and wind tunnel (WT) testing, have been carried out at the Institute for Aerospace Research (IAR) to investigate the wind-loading effects on the prototype, spherical Canadian/US Very Large Optical Telescope (VLOT) structure. The VLOT is currently in the first phase of design and these preliminary studies were part of an IAR/HIA (Herzberg Institute of Astrophysics) collaboration supporting the development of an integrated design model (IM) of the VLOT. The 51-m-diameter enclosure is spherical in shape, with the lower one-quarter removed to provide a flat base. The opening through which the telescope sees is 24 m in diameter and can be positioned at a range of zenith (elevation) angles from 0° to 60° for the full 360° azimuth range. The primary purpose of the CFD/WT studies was to assess the capability of a fully unsteady Lattice-Boltzmann CFD code to predict wind loads on the enclosure and telescope structures for use in telescope design by performing comparisons with the wind tunnel measurements. Both cavity resonance due to flow over the opening and vortex shedding from the spherical structure were observed in the wind tunnel experiments and the CFD computations. The CFD code predicted three simultaneously excited cavity modes that were identical to those measured.