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A numerical investigation of three-dimensional turbulent airflow around WFCAM at the UK Infrared Telescope

Recent advancements in computational fluid dynamics (CFD) software development (namely incorporation of unstructured meshing, wall functions and advanced turbulence modeling) now make it possible to perform a full three dimensional turbulent airflow analysis without the need for a supercomputer. A commercially available CFD code was used to investigate the effect of the WFCAM (a wide field camera developed by Astronomy Technology Centre at Royal Observatory of Edinburgh) presence in the airflow through the optical path of the United Kingdom Infrared telescope (UKIRT). The necessity of this investigation arises from the fact that WFCAM is placed directly above the primary mirror of the UKIRT telescope. There is very little information available in the literature about the possible adverse effects of this configuration on telescope performance, namely seeing and additional wind loading. The CFD code chosen to carry out the study utilizes a wall function for treatment of the near-wall solution. This approach requires only one node in the boundary layer and results in a significant reduction of required computing capacity. The results presented in the study include the effects of turbulent fluctuations of the airflow, natural and forced convection, and wind loading predictions on the instrument with the telescope at several positions.