Impact of Resonance Loading on the Sound Generation from In-Duct Point Sources

Kurzfassung

Analytical models of the sound generation from ducted turbomachinery stages often apply spatially distributed point sources such as monopoles and dipoles, which can be derived from the in-duct Green's function. Another important application of point source models is the localisation of sound source distributions, which is done inside ducts so far mainly for fan stages. One difficulty with current point source models is the unconstrained excitation of resonant modes at their cut-on frequencies leading to unrealistically high sound power levels. Simultaneously, the resonant modes manifest an immense loading on the point sources according to Newton's third law. To achieve more realistic predictions, an extension of the point source models is developed that accounts for the impact of resonance loading by including an internal source impedance. The resulting sound power distribution over the range of cut-on modes is derived for relevant source configurations and compared with reference models and experimental data from a fan test rig.