Wave-field structure in active bubble systems in shock tubes with “discontinuities” in cross section

The wave structure in active bubble media in shock tubes with sudden changes of profiles in the form of “discontinuities” in cross section and a one-phase liquid waveguide is analyzed numerically. In axisymmetric formulation, the paper studies wave amplification due to reflection from a wall and focusing at the butt-end of a rigid rod aligned coaxially with the channel. In this configuration, the amplification effect results from two-dimensional cumulation of the shock wave after it leaves the annular channel and reaches the butt-end of the rod. A Mach configuration forms in the focus spot. The geometrical characteristics of the shock tube allow one to control (to some extent) the amplification coefficient and the coordinates of the focus spot. In particular, it is shown that the wave can be focused near the second discontinuity of cross section – a rigid wall (in the region of passage through the interface to the waveguide) – and intensified upon reflection. If the waveguide radius is equal to the height of the Mach stem, the reflected wave has a maximum amplitude.