CFD Application for the Characterization of Surface Pressures on Telescopes

Aerodynamic trade studies in support of an interdisciplinary research program for large ground based telescopes are addressed. Numerous CFD (Computational Fluid Dynamics) trade studies were carried out to help identify the initial critical configuration of the telescope. The highest pressures induced on the reflective surface of the telescope mirror in the critical configuration were used in structural analysis. A module that correlated disparate discretizations in structural and fluid analyses through common parent geometry was developed. This module mapped surface pressures from the CFD discretization to the structural discretization using a weighted average technique. Experimental validation of the CFD results was carried out in the University of Kansas subsonic wind tunnel. The results from the CFD analysis and the wind tunnel experiments were in close agreement, with the maximum variation of pressures being 1%–8%. The preliminary telescope configuration that induced the highest pressure on the reflective surface of the primary mirror was identified as one inclined at 60° from the vertical plane and facing the wind directly. An “open-air” CFD model was developed that simulated the observatory shut-off operating conditions of 15 m/s wind speed and a fail-safe operating condition of 50 m/s wind speed. Critical local total gage pressures were 165 Pa and 1400 Pa at 15 and 50 m/s wind speeds respectively.