G. Rubio, Numerical methodologies for the determination of noise sources in subsonic flows, 2007

Abstract

Computational aeroacoustics deals with the computation of noise generated aerodynamically. In order to solve this problem, and given the difference between flow and acoustic scales, the direct computation of aeroacoustic noise by solving the compressible unsteady Navier-Stokes equations for the whole domain of interest, becomes prohibitively expensive for most of industrial applications. In order to overcome the computational burden while preserving an engineering accuracy level, hybrid methods emerge, where the noise source generation and the noise propagation are computed separately. In these hybrid methodologies, aeroacoustic sources are first identified by solving the compressible Navier-Stokes equations in a reduced domain. Then, these sources are introduced in a set of suitable propagation equations like the Linearized Euler Equations or the Acoustic Perturbation Equations. The cost of solving these propagation equations is much lower than it would be if the Navier-Stokes equations have to be solved all the way to the far field.

The quality of the aeroacoustic sources identified in the first step is of paramount importance in order to obtain accurate results for the sound pressure level in the medium-far field. When solving the Navier-Stokes equations in order to identify these sources, turbulence can be approached in different ways. In Large Eddy Simulation, the Navier-Stokes equations are filtered, and only the big, energy containing eddies are resolved, whereas the small scales of turbulence and its influence in the resolved scales has to be modeled with a subgrid scale model. This approach is different from Direct Numerical Simulation, where all the turbulent scales are resolved. The grid size and the computational power needed for a Large Eddy Simulation is orders of magnitude smaller than what is needed for a Direct Numerical Simulation, making the first approach, again, much more attractive for industrial applications.

The purpose of this research is to develop numerical techniques that allow for an accurate computation of noise sources using Large Eddy Simulation, as well as to make an assessment of the real capabilities of hybrid methodologies for subsonic flows.

Order Code

Code: 07D12