TITLE:
Attenuation Effect of Expansion Configuration and Acoustic Material on Propagation of Blast Waves in a Duct
AUTHORS:
Motonobu Ishiguro, Kenji Shinkai, Ryo Shimamura, Hironobu Gunji, Yoko Takakura
KEYWORDS:
Blast Wave, Shock Tube, Exhaust Noise, Decay Factor, Silencer Model, Acoustic Material
JOURNAL NAME:
Journal of Flow Control, Measurement & Visualization,
Vol.4 No.3,
July
12,
2016
ABSTRACT: With recent increase of cars, the noise problem has been caused by the exhaust sounds released from exhaust pipes, which consist of weak and pulsed shock waves called blast waves. To diminish the noise, a silencer is set up in front of the exhaust pipe. In the present study, reflectors were installed in the high-pressure section of the shock tube to generate blast waves, and three types of expansion region were investigated, combined with acoustic material of glass wool. The pressure decay was evaluated by transmission factor and reflection factor for the incident blast wave, together with pressure histories and high-speed Schlieren photography. As results, it was confirmed that the acoustic material greatly contributed to blast-wave attenuation: the one stage expansion model with glass wool recorded the highest decay of the peak over pressure for transmission, and other models with glass wool showed the second highest. The acoustic material also contributed to decay of reflected shock waves propagating toward an upstream duct.