Investigação Experimental da Adição de Energia por Laser em Escoamento Hipersônico de Baixa Densidade

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The possibility of reducing the aerodynamic drag and heating of a hypersonic vehicle by addition energy to the air ahead of it is an attractive idea directed toward the hypersonic field. (Mach>5) and can be realized by laser induced plasma generation. In this context, this work presents original results in the experimental investigation of the energy addition in hypersonic flow of low density using two high power lasers. The experiments were conduced in a hypersonic shock tunnel and the results were obtained using two methods: the schlieren visualization technique and the measurement of the impact pressure over a model installed in the tunnel test section. A hemispherical model, 55 mm diameter, equipped with a pressure transducer in the stagnation point, was installed in test section of the tunnel to measure the pressure reduction by energy addition ahead of it. Two high power pulsed CO2 TEA lasers sharing the same optical cavity were mounted to generate two collinear optical pulses with controlled time delay to realize the experiments, the assembly was operated in the energy range of 4 J to 7 J corresponding to peak power of 16.5 MW to 30 MW. To elucidate the effects of laser-induced plasma in hypersonic flow, the non-intrusive schlieren visualization technique associated with a high-speed camera were adopted for the visualization the time evolution of the energy addition to the low density hypersonic flow. Most of the experiments simulated a 22 km, Mach 7, hypersonic flying conditions with stagnation temperature of 1,300 K and velocity of 1.6 km/s, but stagnation temperature of 4,700 K, Mach 5.6 and velocity of 3.4 km/s were also tested. Four time delays between pulses, 30, 40, 50, and 80 µs, were selected to study the effects of multi-pulses interaction and the transition from the occurrence of the superposed effects of the pulses to the situation where the flow regenerates the bow shock in the transition between pulses was obtained. Also, the conditions to obtain a laser-assisted hypersonic flight performed with energy addition benefits at steady state regime were obtained. The schlieren technique produced images with a wealth of details about the dynamics of the energy addition to the hypersonic flow by laser induced plasma and a good correlation with the quantitative results collected by the pressure transducer at stagnation point was obtained. Excellent images showing the mitigation of the bow shock were acquired adding energy to the flow upstream of the model. Aside the academic objective of the thesis, the upgrades generated by this work to the laboratory as the schlieren and lasers incorporated to the facilities had contributed to its inclusion in the USAF hypersonic program.

ASSUNTO(S)

interação laser-plasma laser-plasma interaction schlieren redução de arrastro aerodinâmico schlieren aerotermodinâmica hypersonic hipersônica drag reduction aerothermodynamics

ACESSO AO ARTIGO

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