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Proceedings Paper

Numerical laser beam propagation using a Large Eddy Simulation refractive index field representing a jet engine exhaust
Author(s): Lars Sjöqvist; Markus Henriksson; Ekaterina Fedina; Christer Fureby
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Paper Abstract

The exhaust from jet engines introduces extreme turbulence levels in local environments around aircrafts. This may degrade the performance of electro-optical missile warning and laser-based DIRCM systems used to protect aircrafts against heat-seeking missiles. Full scale trials using real engines are expensive and difficult to perform motivating numerical simulations of the turbulence properties within the jet engine exhaust. Large Eddy Simulations (LES) is a computational fluid dynamics method that can be used to calculate spatial and temporal refractive index dynamics of the turbulent flow in the engine exhaust. From LES simulations the instantaneous refractive index in each grid point can be derived and interpolated to phase screens for numerical laser beam propagation or used to estimate aberration effects from optical path differences. The high computation load of LES limits the available data in terms of the computational volume and number of time steps. In addition the phase screen method used in laser beam propagation may also be too slow. For this reason extraction of statistical parameters from the turbulence field and statistical beam propagation methods are studied. The temporal variation of the refractive index is used to define a spatially varying structure constant. Ray-tracing through the mean refractive index field provides integrated static aberrations and the path integrated structure constant. These parameters can be used in classical statistical parameterised models describing propagation through turbulence. One disadvantage of using the structure constant description is that the temporal information is lost. Methods for studying the variation of optical aberrations based on models of Zernike coefficients are discussed. The results of the propagation calculations using the different methods are compared to each other and to available experimental data. Advantages and disadvantages of the different methods are briefly discussed.

Paper Details

Date Published: 12 October 2010
PDF: 12 pages
Proc. SPIE 7836, Technologies for Optical Countermeasures VII, 78360K (12 October 2010); doi: 10.1117/12.865031
Show Author Affiliations
Lars Sjöqvist, Swedish Defence Research Agency (Sweden)
Markus Henriksson, Swedish Defence Research Agency (Sweden)
Ekaterina Fedina, Swedish Defence Research Agency (Sweden)
Christer Fureby, Swedish Defence Research Agency (Sweden)

Published in SPIE Proceedings Vol. 7836:
Technologies for Optical Countermeasures VII
David H. Titterton; Mark A. Richardson, Editor(s)

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