Evaluation of the aero-optical properties of the SOFIA cavity by means of computional fluid dynamics and a super fast diagnostic camera

Christian Engfer; Enrico Pfüller; Manuel Wiedemann; Jürgen Wolf; Thorsten Lutz; Ewald Krämer; Hans-Peter Röser

doi:10.1117/12.926272

17 September 2012 Evaluation of the aero-optical properties of the SOFIA cavity by means of computional fluid dynamics and a super fast diagnostic camera

Christian Engfer, Enrico Pfüller, Manuel Wiedemann, Jürgen Wolf, Thorsten Lutz, Ewald Krämer, Hans-Peter Röser

Author Affiliations +

Proceedings Volume 8444, Ground-based and Airborne Telescopes IV; 844412 (2012) https://doi.org/10.1117/12.926272
Event: SPIE Astronomical Telescopes + Instrumentation, 2012, Amsterdam, Netherlands

Abstract

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a 2.5 m reflecting telescope housed in an open cavity on board of a Boeing 747SP. During observations, the cavity is exposed to transonic flow conditions. The oncoming boundary layer evolves into a free shear layer being responsible for optical aberrations and for aerodynamic and aeroacoustic disturbances within the cavity. While the aero-acoustical excitation of an airborne telescope can be minimized by using passive flow control devices, the aero-optical properties of the flow are difficult to improve. Hence it is important to know how much the image seen through the SOFIA telescope is perturbed by so called seeing effects. Prior to the SOFIA science fights Computational Fluid Dynamics (CFD) simulations using URANS and DES methods were carried out to determine the flow field within and above the cavity and hence in the optical path in order to provide an assessment of the aero-optical properties under baseline conditions. In addition and for validation purposes, out of focus images have been taken during flight with a Super Fast Diagnostic Camera (SFDC). Depending on the binning factor and the sub-array size, the SFDC is able to take and to read out images at very high frame rates. The paper explains the numerical approach based on CFD to evaluate the aero-optical properties of SOFIA. The CFD data is then compared to the high speed images taken by the SFDC during flight.

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Christian Engfer, Enrico Pfüller, Manuel Wiedemann, Jürgen Wolf, Thorsten Lutz, Ewald Krämer, and Hans-Peter Röser "Evaluation of the aero-optical properties of the SOFIA cavity by means of computional fluid dynamics and a super fast diagnostic camera", Proc. SPIE 8444, Ground-based and Airborne Telescopes IV, 844412 (17 September 2012); https://doi.org/10.1117/12.926272

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