超声速调制气流声源声压级增益特性的理论与实验

通常认为,当气室压力提高到一定程度,调制气流声源声压级输出将趋于饱和。为了从基本原理上探讨进一步提高声源输出的途径,设计了收缩-扩张喷口,将调制作用上游的声速流动提高至超声速。理论分析表明,来流气压较高时,超声速调制优于声速调制,可获得一定的声压级增益。增益量随喷口面积比减小而增加。旋笛实验在调制频率较低时得到了超声速调制的声压级增益;调制频率较高时,受瞬态作用的影响,参与调制的气流很可能未完全发展为超声速流动,超声速调制与声速调制的旋笛性能相同。

Research on the Performance of a Supersonic Flow Modulated Speaker

It is well known that the sound pressure level (SPL) of air-modulated speaker (AMS) finally reaches saturated when the chamber pressure increases. As a new approach to obtain higher SPL output, supersonic flow modulation was discussed in which the flow speed of nozzle exit is increased from sonic to supersonic. Results from the quasi-steady theory have proved that, when the chamber pressure is high, the SPL in the supersonic case is higher than that in the sonic case. Larger SPL increments generally appear at smaller nozzle area ratio. The improvement of the source intensity was validated by the comparison of sound measurements between the sonic and supersonic cases in low frequency modulation. But in high frequency modulation, due to the transient flow effect, the SPL in the supersonic case is the same as that in the sonic case while the air jet is considered to be not fully developed or speed up to supersonic.