Computational Aeroacoustics for Rotating Systems with Application to an Axial Fan

A hybrid aeroacoustic formulation, which is well suited for the computation of rotating systems, is presented. It is based on a decomposition of flow (incompressible part) and acoustic (compressible part) quantities, is applicable to high-Reynolds-number and low-Mach-number flows, accounts convective effects on the wave propagation, and features only a scalar unknown (i.e., the acoustic velocity potential), thus reducing the computational effort significantly. To show the accuracy and applicability of our approach, the proposed method is applied to an axial fan. Thereby, the experimental setup is discussed in detail, and measurements are performed toward the flow and acoustic field. Furthermore, the computation of the flowfield is presented along with the evaluation of the acoustic source terms, its efficient and accurate interpolation to the acoustic grid, and the computation of the generated acoustic sound. The comparison of local and global physical quantities, both for the flow as well as for acoustics, shows good agreement and demonstrates the applicability of the present aeroacoustic approach for rotating systems.