Experimental Investigation on the Reduction of Railway Tunnel Sonic Boom.

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  • トンネルソニックブームの軽減法に関する実験的研究
  • トンネル ソニックブーム ノ ケイゲンホウ ニ カンスル ジッケンテキ ケンキ

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Sonic booms which were generated by the entrance of a high-speed train into a tunnel were experimentally reproduced using a scaled tunnel sonic boom simulator, whose test section was a tube with diameter 40 mm and length 25 m. An 18-mm-diam., 200-mm-long cylindrical piston was launched into the test section, so that a shock wave was emitted from the exit of the test section. An impulsive pressure wave, that is, the source of the sonic boom, was experimentally reproduced. A hood installed at the entrance of the test section effectively delayed the formation of the shock wave, thereby reducing the sonic boom. This method was effective in the range of relatively low piston speeds. By installing a 0.5-m-long porous wall at the exit of the test section, the pressure gradient of the shock wave became finite and the peak overpressure was decreased. Even in the case that the wall was only partially covered with the porous material, the poromeric effect was significant, in particular, for high piston speeds. When the hood at the entrance and the partially installed porous material on the exit wall were combined, the reduction of the peak overpressure became 50 to 80% in the range of the piston speeds from 60 m/s to 100 m/s.

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