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

摘要

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