Negative Impulsive Wave Caused by Discharging Unsteady Expansion Wave from an Open End of a Tube

A compression wave discharged from an open end of a tube causes positive impulsive noise. Active noise cancellation which is the cancelling of the noise by the addition of an inverse wave is a useful technique for reducing impulsive noise. The final objective of this study is to present the design for a negative impulsive wave generator utilizing unsteady mass influx. In this paper, in order to clarify the relationship between the unsteady mass influx and the negative impulsive wave, experimental investigations have been carried out using an unsteady expansion wave discharged from an open end of a shock tube, together with the numerical and aeroacoustic analyses. As a result, the effect of an unsteady expansion wave on a negative impulsive wave was shown, and then a suitable choice of design factors for the generator was discussed.