WAVE FRONT SPEED AND GROUP VELOCITY IN BUBBLY FLUIDS

摘要

This work considers one-dimensional linear acoustic wave propagation in bubbly fluids. Transient wave propagation is of particular interest and studied in some detail. The prime objective is to demonstrate that the wave front speed of a pulse can be lower than the maximum values of both the phase- and group velocities at finite frequencies. A bubbly fluid is considered for the case of bubbles of one size. For finite frequencies, both the phase- and group velocities become larger than the wave front speed. Moreover, in a certain frequency region, the group velocity becomes negative and even infinite. This displays that one has to be careful in interpreting properties of wave propagation by means of the group velocity concept.