Operational model for VLT temperature and flow control

Volker Baeumer; Philippe Sacre

doi:10.1117/12.269094

21 March 1997 Operational model for VLT temperature and flow control

Volker Baeumer, Philippe Sacre

Proceedings Volume 2871, Optical Telescopes of Today and Tomorrow; (1997) https://doi.org/10.1117/12.269094
Event: Optical Telescopes of Today and Tomorrow, 1996, Landskrona/Hven, Sweden

Abstract

This paper describes the operational model for control of thermal and wind flow environment inside ESO's very large telescope (VLT). The purpose of this model is to manage the local seeing in an optimal way using the systems available in the VLT. The technique applied for optimal temperature control is first discussed. Given a meteorological forecast for the ambient temperature of the following night, a model-based procedure can determine the optimal air cooling temperature set point and mirror back plate cooling time histories in order to minimize a performance index related to seeing. Using temperature sensors in the VLT, this procedure will, in practice, constantly be repeated throughout day and night in a fixed horizon predictive control manner. Results of extensive wind channel measurements are then presented. The average root-mean-square (rms) value of turbulent pressure fluctuations on the primary mirror has been measured for various opening configurations and wind directions. Based on a correlation between wavefront aberration an the average rms pressure, the optimal ventilation configuration can be chosen, with the additional constraint of maximizing enclosure flushing. Measured values for wind velocities on the primary mirror can be used in the thermal model for evaluating forced convective exchanges. The integrated model, coupling aerodynamical and thermal optimization, is then presented, an its implementation for the VLT is discussed, as well as further ideas for improvement.

Citation Download Citation

Volker Baeumer and Philippe Sacre "Operational model for VLT temperature and flow control", Proc. SPIE 2871, Optical Telescopes of Today and Tomorrow, (21 March 1997); https://doi.org/10.1117/12.269094

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