Focusing of nonlinear waves emitted from a source of large aperture angle

Yano, Takeru
July 2000
AIP Conference Proceedings;2000, Vol. 524 Issue 1, p221
Academic Journal
Propagation of focused nonlinear waves in an ideal gas is numerically studied by solving the axisymmetric Navier-Stokes equations with a finite-difference TVD scheme. The sound source is a phased array, whose geometrical focal length is the half of its radius. Computed is the case of focusing gain 62.8, where the wave emitted by harmonic oscillations of the source converges like a spherical wave at a focal region. Large-scale and accurate computations clarify the following features. When the acoustic Mach number on the source is 0.0036, the wave profile evolves into a shock in the focal region. The local Mach number reaches a peak of 0.3 at about the geometrical focus and the maximum excess pressure attains 56% of an ambient pressure slightly before the focus. Narrow jet-like streaming (mean mass flow) is induced on the axis. The maximum streaming Mach number is almost 0.06 and the jet width is less than a sixth of typical wavelength. The time-averaged temperature rises in a narrow region along the jet. The temperature elevation exceeds 2% of the ambient temperature.


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