轴对称和球对称流体流动的声学层位
Acoustic horizons for axially and spherically symmetric fluid flow
摘要：
本文研究了无粘流体在管内运动时，在静止和轴对称流动情况下，声波视界的形成。我们表明，不同于通常认为的，声学地平线的形式对应于局部最小或最大的通量管截面。类似地，要求外势在视界处有最大值或最小值，这样外力在视界处就为零。选择幂律流体状态方程$P\propto ρ^{n}$，求解流体动力学方程，并证明了这两种可能性分别对$n>-1$和$n<-1$实现。这些结果也推广到球对称流的情况。
英文摘要：
We investigate the formation of acoustic horizons for an inviscid fluid moving in a pipe in the case of stationary and axi-symmetric flow. We show that, differently from what is generally believed, the acoustic horizon forms in correspondence of either a local minimum or maximum of the flux tube cross-section. Similarly, the external potential is required to have either a maximum or a minimum at the horizon, so that the external force has to vanish there. Choosing a power-law equation of state for the fluid, $P\propto ρ^{n}$, we solve the equations of the fluid dynamics and show that the two possibilities are realized respectively for $n>-1$ and $n<-1$. These results are extended also to the case of spherically symmetric flow.
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