### ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

## 4pPAa8. Generation of streaming and rarefaction of the gas in the far
field of the weakly nonlinear plane waves.

**Takeru Yano
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Yoshinori Inoue
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*Dept. of Eng. Sci., Hokkaido Univ., Sapporo 060, Japan
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The propagation of weakly nonlinear plane waves emitted from a
harmonically oscillating plate into an ideal gas of semi-infinite extent is
considered under the condition that the energy dissipation is negligibly small
everywhere except for discontinuous shock fronts. Recently, the authors have
numerically shown that, in the case of strongly nonlinear waves, contrary to
the result of the conventional weakly nonlinear theory, streaming due to shocks
occurs in the direction of wave propagation and thereby the gas near the source
is rarefied as time proceeds [Y. Inoue and T. Yano, J. Acoust. Soc. Am. 94,
1632--1642 (1993)]. In the present paper, the evolution of the weakly nonlinear
waves including shocks is determined up to O(M[sup 2]), where M is the acoustic
Mach number (M<<1). In this order, the wave profile develops to an asymmetrical
sawtoothlike one in the far field and weak streaming is excited in the region
beyond the shock formation distance. For M(less than or approximately equal
to)0.2, the results quantitatively agree with those in the previous work.
Furthermore, by taking into account both the production of entropy and the
generation of reflected wave at each shock front, the physical mechanism is
clarified for the rarefaction of the gas in O(M[sup 3]).