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Computational Fluid Dynamics tool developed at GMTO

The below movies are examples of the Computational Fluid Dynamics simulation tool developed at GMTO by Konstantinos Vogiatzis and Kaushik Das.

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What you are seeing above is a simulation of the GMT enclosure – the building that protects the telescope from the elements – and the air flow through it. Even though they are not visible here, we include in the simulation all the buildings on the summit, such as the coating chamber and summit offices.

These lines are not precisely the airflow however: technically they are the “magnitude of the spatial gradient of the refractive index of air on a plane parallel to the wind and aligned with the enclosure symmetry axis”. What this means in practice is this simulation shows the regions of optical turbulence – or random variations in air speed and temperature– that can affect the image quality of the telescope.

Above we can see the seven mirrors that make up the GMT. What looks like clouds passing over the mirrors is actually a representation of how turbulent mixing of air affects image quality. In the absence of air all light rays travel the same distance and arrive at the mirror at the same time. Turbulence in the air causes some rays to travel longer distances – yellow areas – or shorter distances – blue areas. The difference is comparable to the thickness of human hair but enough to cause a star to “twinkle”.

We run these simulations with various orientations of the telescope relative to the wind and for different environmental conditions such as temperature and wind speed. We analyze all this information to understand which aspects of the design of the enclosure negatively affect image quality, and what can be done about it.

Some design choices we can make include aerodynamic streamlining of the enclosure, optimizing the cladding material, active temperature control, and working on ways to minimize heat release into the air in front of the telescope.

As the design of the enclosure moves into its final stages these kinds of simulations are important to ensure our design guarantees the best possible image quality from the telescope.

The input environment for the simulations. The simulation environment includes a 12x12x5 square kilometer topographical area around the telescope. Inputs to the simulation include upwind wind velocity, upwind thermal gradient, as well as ambient temperatures on the telescope.