A combined time and frequency domain approach for acoustic resonance prediction

A general hybrid time- and frequency-domain methodology has been developed to identify acoustic resonance conditions of internal flow configurations. The acoustic modes are determined by imposing onto the flow a time-dependent excitation at several locations on the boundary. The resulting time-domain pressure responses, which are computed via an unsteady Favre–Reynolds averaged Navier–Stokes solver, are used to determine the frequency response function matrix of the fluid which can be considered to be a multiple-input multiple-output system. The main test case was selected to be a closed-end cylindrical duct for which the effect of different excitation techniques on the predicted acoustic modes is discussed in detail. The last test case deals with the acoustic characterization of a 2-D channel with symmetric bumps and an inlet flow velocity of 17ms-1. It is shown that the methodology was suitable for identifying axial and transverse acoustic modes up to 3 kHz.