Viscothermal Wave Propagation including Acousto-elastic Interaction, Part I: Theory

This research deals with pressure waves in a gas trapped in thin layers or narrow tubes. In these cases viscous and thermal e!ects can have a signi"cant e!ect on the propagation of waves. This so-called viscothermal wave propagation is governed by a number of dimensionless parameters. The two most important parameters are the shear wave number and the reduced frequency. These parameters were used to put into perspective the models that were presented in the literature. The analysis shows that the complete parameter range is covered by three classes of models: the standard wave equation model, the low reduced frequency model and the full linearized Navier}Stokes model. For the majority of practical situations, the low reduced frequency model is su$cient and the most e$cient to describe viscothermal wave propagation. The full linearized Navier}Stokes model should only be used under extreme conditions. ( 1999 Academic Press