Normal‐mode theory of enclosures with thermoviscous dissipation at the walls

Abstract

This paper treats a limiting case of normal‐mode theory for which all of the dissipation occurs in the thermoviscous boundary layer in the fluid near the walls. This case differs from that of finite‐impedance walls primarily in its more complicated dependence of the viscous dissipation on the mode numbers. The normal‐mode theory with infinite‐impedance walls is shown on a term‐by‐term basis to be equivalent to the Kirchhoff tube theory. An example of how one might exploit this equivalence is given. Calculated absorption coefficients for infinite‐impedance walls are compared with the experimental coefficients in the literature.