The performance requirements of the Thirty Meter Telescope (TMT) dictate, among others, a thorough understanding of the flow field inside and around the observatory. Mirror and dome seeing as well as dynamic wind loading on the optics, telescope structure and enclosure constitute significant sources of image degradation. A summary of the current status of Computational Fluid Dynamics (CFD) simulations for TMT is presented, with special attention given to the choice of thermal boundary conditions. Detailed simulations of the mirror support assemblies determine the direction of heat flow from important heat sources and provide feedback to the design. They also provide estimates of the heat transfer coefficients for the solid thermal models. A transient radiation model has also been developed for the enclosure and telescope surfaces in order to estimate the heat flux exchange with the air volume. It also provides estimates of the effective emissivity for the solid thermal models. Finally, a complete model of the observatory on a candidate summit is used to calculate air velocity, pressure and temperature for a matrix of given telescope orientations and enclosure configurations. Calculated wind velocity spectra above M1 and around M2 as well as the wind force on the enclosure are used as inputs in the TMT integrated dynamic model. The temperature and flux output of the aforementioned thermal models are used as input surface boundary conditions in the CFD model. Generated records of temperature variations inside the air volume of the optical paths are fed into the TMT thermal seeing model.

Date Published: 7 July 2008
PDF: 11 pages
Proc. SPIE 7017, Modeling, Systems Engineering, and Project Management for Astronomy III, 70170Q (7 July 2008); doi: 10.1117/12.787922

Published in SPIE Proceedings Vol. 7017:
Modeling, Systems Engineering, and Project Management for Astronomy III
George Z. Angeli; Martin J. Cullum, Editor(s)