Investigation of the acceleration of aluminum particles behind a shock wave using instantaneous Laser Doppler Velocimetry |
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Authors: | G Schlöffel M Bastide S Bachmann Ch Mundt F Seiler |
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Institution: | 1. French-German Research Institute of Saint-Louis (ISL), 5 rue du Général Cassagnou, 68300, Saint-Louis, France 2. Fakult?t für Luft- und Raumfahrttechnik, Institut für Thermodynamik, Universit?t der Bundeswehr München, Werner-Heisenberg-Weg 39, 85577, Neubiberg, Germany
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Abstract: | The acceleration of aluminum particles with a 5μm diameter in the flow field behind an incident shock wave was investigated
experimentally in a 10-m long and 70 mm inner diameter shock tube. By means of instantaneous Laser Doppler Velocimetry (LDV)
the velocity of the particles was observed directly. The light scattered by the moving particles is Doppler shifted and sent
to the laser Doppler velocimeter. The velocimeter essentially consists of a phase-stabilized Michelson interferometer used
as a sensitive spectrometer. An electro-optical circuit ensures the phase stabilization that results in a voltage signal independent
of the scattered light intensity and proportional to the mean velocity of the particles at the measurement point. Because
of the very short response time (1μs) of the LDV system used here, the latter gives a continuous real-time signal of the particle
acceleration. To avoid particle oxidation the particles were accelerated by a high-speed nitrogen gas flow. From the measured
velocity the dimensionless drag coefficient was calculated. The drag coefficient is related to the fluid dynamic force exerted
by the gas on the particles. The experimental data were compared to theoretical models from the literature. A significant
deviation between the model and the experimental data was observed. This deviation is supposed to be induced by the shock
wave, which hits the particles and breaks them into pieces of a smaller diameter. Further experiments will be carried out
in the future to check the size distribution of the particles after the shock has gone past them.
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Keywords: | Laser Doppler Velocimetry Velocity measurements Aluminum particles Shock wave Multiphase flow |
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