スピーカーによる音場が拡散火炎に与える影響に関する実験的研究

抄録

The effects of the traveling sound wave generated by the speaker on diffusion flame were investigated experimentally. The sound frequency was varied from 50 to 1000 Hz using two sizes of loudspeakers, whose peak frequency showing the maximum sound pressure amplitude is nearly identical. A spirit lamp was used as the reference (diffusion) flame. Having irradiation of sound, the flame was inclined and stretched toward the traveling direction under specific range of the exposed frequencies and importantly, the effective range of the frequency was found to be quite different in two speakers used in this study. Precisely speaking, the deformed flame length reached its maximum value under the condition of 200 to 400 Hz for small speaker and 50 to 200 Hz for large speaker, respectively. In addition, the velocity distribution around the speaker was measured to reveal that the variation of flame length with respect to frequency, and it was found that the response against the applied frequency was rather close to that of flow velocity, not that of the acoustic pressure amplitude. Further investigation of flow field nearby the speaker clearly showed that the pump-like flow acceleration was induced by the periodic motion of the membrane of the speaker. From the above results obtained, it was confirmed that the effect of acoustic sound on the flame shall be come not only from pure acoustic wave feature but also from the factors depending on the hardware. Without the eliminating the latter effect, nature of acoustic-flame interaction behavior by using acoustic characters (e.g., frequency or acoustic pressure) is not readily available.