Progress in time-domain calculations of ducted fan noise - Multigrid acceleration of a high-resolution CAA scheme

Abstract

The numerical simulation of an aeroacoustics problem using the full, time-dependent Euler or Navier-Stokes equations requires both the mean and unsteady flow fields. Sometimes the mean flow is equivalent to the steady state flow and used to start the unsteady solution process. In this case, both the steady and unsteady flow fields have to be obtained through the same numerical method, so that the restart process is smooth and no spurious waves are generated. However, due to its low dissipation and consequently slow convergence, a high-resolution computational aeroacoustics scheme is not suitable for computing the steady flow field. In this paper, such a scheme is accelerated to convergence, without altering its residual, by using a full approximation storage multigrid method for the prediction of ducted fan noise. It is demonstrated that significant convergence improvements axe obtained using the multigrid method, making it possible to attain steady state solutions on extremely fine meshes designed for highfrequency radiation problems. Far-field noise results for a JT15D inlet are presented and compared with data at realistic flight configurations.