THE ACOUSTIC BOUNDARY-LAYERS - A DETAILED ANALYSIS

[摘要] The viscosity of the medium plays an important role in defining the characteristics of sound wave propagation in ducts. This effect, due to the difficulty of analysis, has been either completely neglected in the literature or considered only approximately. In this study, a mathematical model is constructed to describe the physical problem in its general form without imposing assumptions a priori. The physical quantities have been conveniently expressed in only two nondimensional quantities, a frequency or wave number bK and a Reynolds number Re. The set of equations describing the model is solved in two-dimensional ducts in the case of no mean flow. Closed-form, exact solutions for the acoustic parameters are obtained. The effect of both Re and bK are computed and presented graphically. The results confirm the existence of a small region, the acoustic boundary layer, inside which the acoustic parameters vary very rapidly. For the first time, the values of u, v and p are computed inside the acoustic boundary layer. The profiles of these parameters are presented across the duct width. The widely used assumption that the viscous effect is confined to the boundary layers, and the rest of the field is essentially inviscid is not supported by the current results.

[发布日期] 1994-05-30

[关键词] ACOUSTIC BOUNDARY LAYERS;DUCT ACOUSTICS;VISCOSITY EFFECT;PROPAGATION AND ATTENUATION OF SOUND WAVES