Aeroacoustic Simulation of Double Diaphragm Orifices in an Aircraft Climate Control System

Transient CFD acoustic source prediction and CA propagation studies of a double diaphragm orifice illustrate complex flow and aeroacoustics phenomena, combining shedding structures (tonal noise) and large eddy structures (broadband noise). Such studies are necessary for aircraft climate control systems because such components introduce nonlinearities in the system characterization. In this paper we investigate, through modeling, the noise signature of a given double diaphragm configuration comparing against microphone measurements the predicted noise spectra in the near field (source region) and the predicted propagated sound in the far field, some distance downstream of the source region. A second configuration is then assessed, with the spacing between the orifices doubled, so as to derive confidence that the modeling is accurate in both absolute and differential terms. A novel method is presented for estimating the mesh frequency cut-off from a steady-state CFD calculation; such an estimate gives valuable insight a priori into the local mesh refinement required for a transient CFD calculation to resolve the frequency range of interest. The work described in this paper is part of a wider evaluation into the use of CAA methods for aircraft climate control systems.