Numerical investigation of unsteady aerodynamics and aero-acoustics in a centrifugal fan

The Lighthill equation was transformed into Helmholtz equation in “weak integral form” and Galerkin method was applied to discretize the above equations. Based on acoustic finite element method (FEM), and considering the effects of scattering and reflection on the complex solid surface (impeller and volute), the Ffowcs Williams-Hawking (FW-H) equation coupling unsteady reynolds average Navier-Stokes (UANS) results were used to simulate the noise radiation of a centrifugal fan. There was a good agreement between the numerical results and dynamic pressure testing of volute casing at blade passing frequency (BPF). The results show that the BPF components dominate the acoustic sources characteristic and the volute tongue region close to shroud (belong to impeller exit width) is a primary acoustic sources region. A good agreement has been shown between acoustic FEM method and noise testing results, and the effects of complex solid surface on noise propagation cannot be neglected. The interaction noise induced by periodical impingement between non-uniform flow of impeller exit and volute casing is much bigger than blades dipole noise, serving as the primary noise component of centrifugal fan, and the primary propagation direction is fan outlet duct.