Predicting the aerodynamic performance of the Canadian Very Large Optical Telescope

Abstract

A variety of aerodynamic studies have been completed to assist in the development of an integrated model for the Thirty Meter Telescope. These studies investigated the characteristics of wind loading on the Canadian Very Large Optical Telescope (VLOT) and produced preliminary data for input into the VLOT integrated model. We describe the details of, and present the results from, the computational fluid dynamic (CFD) analyses and wind tunnel (WT) tests. The validity of the CFD results is assessed through correlation studies that compare the CFD and WT results. Through extensive comparison of the mean and RMS coefficients of pressure and the power spectral density plots of the pressures within the enclosure, excellent correlations between the experimental and computational results are shown.

Wind loads on ground-based telescopes

“…6), the loads on M1, 13 and CFD. 7 The wind-tunnel tests were conducted with simplified dome geometries that result in flow fields that are not identical to those expected in realistic domes, and CFD is used to understand the differences.…”

“…Digital particle image velocimetry (DPIV) can provide a quantitative spatial map of the flow field in the region around the secondary mirror, 6 while arrays of pressure measurements across the primary mirror can be used to understand the spatial variation. 13 In addition to the wind-tunnel tests on hemispherical domes that are used to develop the understanding herein, others have recently been conducted for a different dome geometry. 14 Tests have also been conducted for radio telescopes; however, since these typically do not have enclosures to shield them from the wind, the flow field around the telescope is quite different.…”

Parametric modeling and control of telescope wind-induced vibration

“…The oscillation frequency of these modes scales with nσU ∞ /D s , where 0.5 < σ < 1 depends on the geometry. These tones occur in wind-tunnel tests at Caltech 12 and NRC, 13 and in CFD analyses of these geometries, 13,15 and for certain configurations are the dominant source of pressure variations within the telescope enclosure. The observed characteristics of these modes include a large oscillatory pressure throughout the entire telescope enclosure, and a large oscillatory vortex structure in the region of the enclosure near the secondary mirror and supporting structure.…”

“…13 Developing estimates of the forces acting on the secondary mirror and supporting structure is complicated by the desire to predict these forces as a function of the location of the mirror within the dome (i.e. to estimate the benefit from building a slightly larger dome with greater clearance between the secondary mirror and the shear layer).…”

“…9,10 More extensive data under more controlled conditions has been collected in scaled wind-tunnel experiments; while this approach has been used for many years, 11 modern experimental techniques allow significantly more data to be collected. 12,13 Finally, computational fluid dynamics (CFD) [13][14][15] is an ideal design tool, and can take advantage of the experimental data for validation, so that CFD can be used with confidence in future design work. The parametric model of wind forces herein builds on earlier efforts 3,4 by incorporating new information from recent computational and wind tunnel studies.…”