Analysis of Acoustic Wave Propagation in a Thin Moving Fluid

TL;DR

This paper analyzes the propagation of acoustic waves in a thin, moving fluid contained in a 2D tube, proving well-posedness and stability of a recent approximate model for monotonic velocity profiles, with implications for numerical computation.

Contribution

The paper proves the well-posedness and stability of the Bonnet-Bendhia, Durufle9, and Joly model for acoustic wave propagation in a thin moving fluid, providing a quasi-explicit solution representation.

Findings

The model is well-posed with a unique, continuously dependent solution.

Solutions grow at most as t^3 for smooth profiles and t^4 for piecewise linear profiles.

The quasi-explicit solution offers physical insight and computational efficiency.

Abstract

We study the propagation of acoustic waves in a fluid that is contained in a thin two-dimensional tube, and that it is moving with a velocity profile that only depends on the transversal coordinate of the tube. The governing equations are the Galbrun equations, or, equivalently, the linearized Euler equations. We analyze the approximate model that was recently derived by Bonnet-Bendhia, Durufl\'e and Joly to describe the propagation of the acoustic waves in the limit when the width of the tube goes to zero. We study this model for strictly monotonic stable velocity profiles. We prove that the equations of the model of Bonnet-Bendhia, Durufl\'e and Joly are well posed, i.e., that there is a unique global solution, and that the solution depends continuously on the initial data. Moreover, we prove that for smooth profiles the solution grows at most as $t^3$ as $t \to \infty$, and that for piecewise linear profiles it grows at most as $t^4$. This establishes the stability of the model in a weak sense. These results are obtained constructing a quasi-explicit representation of the solution. Our quasi-explicit representation gives a physical interpretation of the propagation of acoustic waves in the fluid and it provides an efficient way to compute numerically the solution.