[in Japanese]

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The present paper describes the effect of duct length on acoustic characteristics of over-expanded jet which are discharged from convergent-divergent nozzle. A duct made of annular metal was installed at the nozzle exit and varied in length from 0 and 6D. A Schlieren optical system is used to visualize detailed jet structures. Acoustic measurement is performed to obtain noise spectra. The results obtained show that the frequency of the acoustic tone due to the shock wave within the nozzle somewhat increases with an increase in the nozzle pressure ratio, and the acoustic tones take place in two stages. The duct devices suppress the acoustic tone and the screech tone.

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When a compression wave generated by a train entering a tunnel is propagated through the tunnel and reaches the exit portal, a pressure pulse ('micro-pressure wave') is radiated from the exit portal. The distortion of the compression wave during propagation in a slab-track tunnel is important for estimating the magnitude of the micro-pressure wave radiated from the exit portal. In this paper, the dependence of the distortion of the compression wave on the initial waveform at the tunnel entrance is investigated theoretically and numerically.

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Flow structures around hypersonic TSTO launch vehicle were investigated by utilizing the electrical discharge method. First, boundary layers near the orbiter surface were observed by a visualization technique of boundary layers. Subsequently, lateral and cross-sectional shock shapes around TSTO launch vehicle were observed by a visualization technique of shock waves. From these results, it was confirmed that a separation shock wave was generated near the orbiter surface. In this study, the visualizations were carried out at Mach 10.

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