Numerical comparison of traditional noise screens and refractive graded index sonic crystal noise barriers in downwind sound propagation

Paper in proceeding, 2012

Sound propagation over a traditional noise screen in downwind conditions is numerically investigated and compared with a graded index sonic crystal (GRIN SC) noise barrier. The latter type of noise barrier creates a shadow zone by upward refraction of waves propagating through. Upward refraction is here achieved by varying the cylinder radius with height hence creating a graded index medium which effective sound speed varies accordingly. Contrary to GRIN SC noise barriers, traditional noise screens aim at improving the sound environment by screening sound emanating from, e.g. traffic noise sources. It has been shown that in downwind propagating conditions traditional solid screens introduce large wind speed gradients above the barrier top, which may give rise to downward refraction of acoustic waves into the shadow zone. In two-dimensional space, wind speed profiles of a traditional screen and an acoustically equivalent GRIN SC noise barrier are numerically computed using computational fluid dynamics. The modeled background flow, treated as an effective sound speed, is then used as input parameter for acoustic propagation calculations. The acoustic performance of both structures including a non-uniform background flow has been evaluated for a simple outdoor setup assuming a hard reflecting ground surface and a single noise source.