Vol 18, No 5

Estimating the mirror seeing for a large optical telescope with a numerical method

En-Peng Zhang, Xiang-Qun Cui, Guo-Ping Li, Yong Zhang, Jian-Rong Shi, Yong-Heng Zhao


Abstract It is widely accepted that mirror seeing is caused by turbulent fluctuations in the index of air refraction in the vicinity of a telescope mirror. Computational Fluid Dynamics (CFD) is a useful tool to evaluate the effects of mirror seeing. In this paper, we present a numerical method to estimate the mirror seeing for a large optical telescope (∼ 4 m) in cases of natural convection with the ANSYS ICEPAK software. We get the FWHM of the image for different inclination angles (i) of the mirror and different temperature differences (∆T) between the mirror and ambient air. Our results show that the mirror seeing depends very weakly on i, which agrees with observational data from the Canada-France-Hawaii Telescope. The numerical model can be used to estimate mirror seeing in the case of natural convection although with some limitations. We can determine ∆T for thermal control of the primary mirror according to the simulation, empirical data and site seeing.


Keywords astronomical instrumentation — methods: numerical — telescopes

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