The acoustic field generated by a shrouded axial fan is numerically analyzed by a hybrid fluid-dynamics-acoustics method. In a first step, large-eddy simulations are performed to investigate the dynamics of tip clearance flow for various tip gap sizes and to determine the acoustic sources. The simulations are performed for a single blade out of five blades with periodic boundary conditions in the circumferential direction on a multi-block structured mesh with 140×10~6 grid points. The results of a Reynolds number of 9.36×10~5 at undisturbed inflow condition are compared with experimental data. The findings show the diameter and strength of the tip vortex to increase with the tip gap size and the efficiency of the fan to decreases. In a second step, the acoustic field is determined by solving the acoustic perturbation equations (APE) on a mesh for a single blade consisting of approx. 1060×10~6 grid points. The overall agreement of the pressure spectrum and its directivity with measurements confirm the correct identification of the sound sources and accurate prediction of the acoustic propagation. The results show that the larger the tip gap size, the higher the broadband noise level.
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