Dissipation of nonlinear acoustic waves in thermoviscous pores

Abstract: We derive a nonlinear acoustic wave propagation model for analysing the thermoviscous dissipation in narrow pores with wavy walls. As the nonlinear waves propagate in the thermoviscous pores, the wave-steepening effect competes with the bulk dissipation, as well as the thermoviscous heat transfer and shear from the pore walls. Consequently, the length scale of the wave is modified. We use the characteristic nonlinear wave thickness scale to obtain linear and nonlinear wave equations governing the unsteady shock-wall interaction. We also perform two-dimensional shock-resolved DNS of the wave propagation inside the pores and compare the results with model equations. We show that for flat-walls and shock strength parameter $\epsilon$, the dimensional wall heat-flux and shear scale as $\epsilon$. For wavy walls, the scaling becomes $\epsilon^{3/2 - n(k)}$ where $k$ is the wall-waviness wavenumber and the exponent $n$ increases from $0.5$ for $k=0$ to $n(k)\approx0.65$ for $k=10$, $n(k)\approx 0.75$ for $k=20$, and $n(k)\approx0.85$ for $k=40$. Hence, increasing the wall waviness reduces the dependence of the wall heat-flux and shear on nonlinear acoustic wave strength.