Einfluss der Geometrie auf die Wirkung von Schallschutzwänden

Noise barriers play an important role in protecting citizens from harmful noise. Standardized and legalized procedures for the planning of simple, upright noise barriers has existed for many years now. The result is that, by simply varying the height of the noise barrier, the desired sound protection is achieved. Sound protection is substantially influenced by the diffraction at the upper edge of the wall. Thus the idea arose that the geometry of the upper edge could be altered through attachments in order to achieve higher acoustical blocking with walls of the same height. Studies show investigations of attachments with different forms and of different materials (absorbing, reflective). Depending on the form, various parameters played a role in the design of such attachments. In the past few years, new noise barriers have been erected during the construction of new traffic routes. More and more, these constructions have upper wall areas that are inclined or even bent. These inclined portions of a noise barrier can be viewed as flap-like attachments. This study investigates the effect of these flap-like attachments on the diffraction by a noise barrier. Despite the presence of studies of noise barriers with T-, Y-, and arrow profiles in the technical literature, the influence of the angle of opening and the lengths of individual flaps of the attachments is not evident. Above all, the results gained during the experiment demonstrate that these parameters are significant; therefore it is important to determine their influence on the shielding effectiveness. To date, theoretical examinations developed a mathematical model that serves as a basis for numerical examinations. The analytical solution for the pressure describes the sound field in front of and behind the noise barrier. Numerical and experimental studies examine the shielding effectiveness achieved through these flap-like attachments, dependent on the attachment parameters “angle of flap opening” and “flap length”. It was discovered that the effect of the attachments was strongly dependent on the source position. Improvements from the attachments were seen only when the angle of the flap opening was greater than that of the source angle. The length of the flap is thus an important parameter with regard to the frequency adjustment of the attachment. The investigation of parameters has shown that a simple basis for the planning of flap-like attachments is not evident. Numerical analyses must be undertaken for practical applications. However, it is also demonstrated that it is possible to use the numerical models applied in this study to be able to predict the effects of attachments.