Sound Propagation above a Porous Road Surface by Boundary Element Method

ABSTRACT A numerical method for the prediction of sound pressure levels nearby roads has been developed and validated. It is based on an integral formulation of the acoustic problem and a numerical solution by Boundary Element Method (BEM). The advantage of such a method is that complex geometries and boundary conditions can be considered. A special care has been taken to integrate air/porous medium interface. This development was validated experimentally by a basic sound propagation case above a porous road surface. In a first part, the basics of sound propagation in the air and in a porous medium are presented. Then, the Boundary Element Method (BEM) model is described along with the specific developments to introduce porous road surface boundary conditions. Then, the validation case of porous road interface treatment in BEM is shown. Finally, the software was successfully applied to two different cases of complex geometries that illustrate the possible use of the model in road environment problems. One studies the combination of noise barrier of sophisticated shape with porous road surface, and suggests that the combined use can give equivalent efficiency at high frequency as the addition of a top device. The second investigates the effect of a porous road surface on the sound amplification of the tire-road noise (horn effect), and shows significant reduction above 1 kHz. However the extension to 3 dimensions is needed to improve realism of this model in the whole frequency range.