Linearized Euler simulations of sound propagation with wind effects over a reconstructed urban terrain using digital geographic information

摘要

The procedure of sound propagation calculation employing the linearized Euler (LE) model has been known to be complex because the procedure requires a chaining of two distinct simulations, namely a fluid dynamics simulation (CFD) in order to solve the background flow field, and a succeeding sound propagation simulation using the LE model over the flow field. The complexity is considered one of the main reasons why the most of the applications of the model remain in investigations assuming highly abstract geometries. In the study, a streamlined workflow is established for LE simulations over a complex urban terrain with its reconstruction utilizing digital geographic models which provide building outline maps and digital surface elevation information. Focus is given to automatic geometry reconstruction and mesh generations of realistic urban terrain. Subsequent processes of CFD and LE simulations are validated through comparisons with published results of wind-tunnel tests and with theoretical solutions. The workflow is deployed to an actual urban terrain of Nagaoka, Japan. The present technique generates a good reconstruction of urban geometry and subsequent split-hexahedral unstructured grid for CFD software and uniform structured mesh for finite-difference LE simulation. The numerical experiments show differences of up to 5 dB between sound pressure levels obtained by the present reconstruction technique and those by a flat-roof geometry. Also, the wind effects are mostly representable in terms of the source-observation point distance in spite of the complex urban configuration. Subtle wind effects of less than 0.5 dB are observed in crosswind condition as well.