Sound propagation near tunnel outlets

This paper investigates the noise propagation in a tunnel by both normal mo de and boundary element methods. The analysis of the sound field close to t he tunnel outlet is the main concern of this study, since the pressure of s ound varies abruptly in this region. The boundary element method is used to construct numerical solutions in this study for convenience. On the other hand, a theoretical analysis of axisymmetric solutions inside circular pipe s with an inclined flange. based on the three-dimensional wave equation and the normal mode method, is set up to verify the numerical results. The convergence of the analytical solutions and the accuracy of the numeric al approach are tested for different pipe-radii and wavelength ratios. Fina lly, the boundary element method, with an approximated radiation condition, is used to simulate a tunnel noise field.