Mildly-Compressible Pressure-Based CFD Methodology for Acoustic Propagation and Absorption Prediction

A modified pressure-based CFD methodology — as commonly used for analysis/design of low Mach number gas turbine combustor flows — is described, which can accurately resolve acoustic wave propagation and absorption. The computational algorithm is based on the classical pressure-correction approach. This is modified to achieve (i) better capture of acoustic waves at reduced number of grid points per wavelength for low dispersion performance, and (ii) incorporation of characteristic boundary conditions to enable accurate representation of acoustic excitation (e.g. via a loudspeaker or siren), as well as acoustic reflection and transmission characteristics. The methodology is first validated against simple test cases demonstrating good numerical accuracy, then compared against classical linear acoustic analysis of acoustic and entropy waves in quasi-1D variable area duct flows. Finally, it is applied to the prediction of experimental measurements of the acoustic absorption coefficient for an orifice flow. Excellent agreement with experimental data is obtained for both linear and non-linear characteristics.