Multidomain Spectral Computations of Sound Radiation from Ducted Fans

Abstract

A time-domain method for acoustic propagation and its application to tone noise radiated from rigid-wall fan inlets are presented. The noise propagation phenomena are modeled by the nonlinear time-dependent Euler equations written in conservative form. The equations are solved numerically using a staggered-grid multidomain Chebyshev discretization for the spatial terms and a Runge-Kutta scheme for time integration. Various types of radiation boundary conditions are implemented and Investigated on generic benchmarks. The resulting code is optimized on parallel machines with shared memory. The method is first validated on noise radiation from two-dimensional and axisymmetric flat ducts with no mean flow for which analytical data exist. The full potential of the method is then tested by computing the sound field radiated from an axisymmetric bell-mouth duct in a nonuniform mean flow. Three-dimensional computations of the sound field in a bent pipe, on which both experiments and computations using a boundary integral method have been carried out at ONERA, are also presented.