Fuchs L., Aberg M., Szasz R.

We consider a moving vehicle behind a noise fence. The generated acoustic field is investigated using a hybrid method. A Mach number expansion of the compressible Navier-Stokes equations results in the incompressible Navier-Stokes equations or the flow field and an inhomogeneous wave equation describing the propagation of acoustic waves. The source term in the latter equation is derived from the flow field variables. The incompressible Navier-Stokes equations are integrated in time using Large Eddy Simulation (LES). These equations are discretized using a high order of accuracy finite difference based scheme. The time-integration allows the resolution of all flow structured that are supported by the used grid. The unresolved components have to be accounted for through the Sub-Grid-Scale (SGS) terms. When the flow field solution is advanced in time, the instantaneous acoustic sources are calculated and interpolated to a separated acoustic grid which is discretized on a much larger (flow independent) grid. The time marching in the acoustic solver can possibly be with different time-step satisfying stability, accuracy and optimized for minimal computational effort. The attenuation and distribution of the acoustic field in the (shadow) zone behind the barrier is investigated in terms of Sound Pressure Level (SPL), directivity and spectral composition. The influence of vehicle velocity on the acoustic signal is expressed in terms of Reynolds number sensitivity