Fourth Australian Conference on Laser Diagnostics in Fluid Mechanics and Combustion
نویسندگان
چکیده
Laser-based missile-defence systems are being increasingly employed on aircraft to provide protection when attacked by optically-guided weapons. In some engagements the laser beam must pass through the exhaust gases of the aircraft. To predict the increase in laser beam divergence and jitter of the laser beam direction, an understanding of the exhaust gas structure and its influence is required. A trial was undertaken where laser photons of three different wavelengths (“2 μm”, “4 μm” and “4.5 μm”) were passed through the exhaust of a well-characterised Gnome jet engine in both turbojet and turbofan configurations, at engine settings from idle to maximum, at two angles (90 and 65 degrees to the plume axis), at various distances from the nozzle (0.5, 1.0 and 1.5 m) and at various vertical displacements (up to 24 cm from the engine plume axis). The effect on the laser beam is determined by analysis of a recorded spot image of the transmitted beam. These results, combined with predictive modelling, will give an insight into the structure and composition of the turbulent gases. Vibration effects are discussed with techniques for reducing the impact of the vibration on the measurement. After correction for these effects, the spot motion data may be used to predict the effect of the turbulent plume on the laser beam.
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