带衬里的流动管道中的慢声laser
Slow sound laser in lined flow ducts
摘要：
本文研究声在具有阻抗壁的波导中的传播。在低频范围内，阻抗的第一个作用是降低声波的传播速度。因此，在低马赫数下，管道中的流动可以超过波的传播速度，使其有效地超音速。我们分析的设置沿壁的阻抗变化，使管道是超音速，然后在一个有限的区域和超音速再次亚音速。在这种特定的配置中，亚音速区域充当谐振腔，并触发类似激光的不稳定性。我们表明，不稳定性是高度亚波长。此外，如果亚音速区域足够小，则不稳定性是静态的。我们还分析了阻抗壁附近的剪切流层的效果。虽然它的存在显著改变了不稳定性，但它的主要性质保持不变。
英文摘要：
We consider the propagation of sound in a waveguide with an impedance wall. In the low frequency regime, the first effect of the impedance is to decrease the propagation speed of acoustic waves. Therefore, a flow in the duct can exceed the wave propagation speed at low Mach numbers, making it effectively supersonic. We analyze a setup where the impedance along the wall varies such that the duct is supersonic then subsonic in a finite region and supersonic again. In this specific configuration, the subsonic region act as a resonant cavity, and triggers a laser-like instability. We show that the instability is highly subwavelength. Besides, if the subsonic region is small enough, the instability is static. We also analyze the effect of a shear flow layer near the impedance wall. Although its presence significantly alter the instability, its main properties are maintained.
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