Numerical prediction of aerodynamic tonal noise radiated from a centrifugal fan

The aerodynamic tonal noise radiated from a centrifugal fan is calculated using a hybrid computational aeroacoustics approach that couples numerical flow with an implementation of the acoustic analogy. The turbulent near field is computed by solving the two-dimensional unsteady Reynolds-averaged Navier-Stokes equations, with k-epsilon turbulence model. The second-order spatial and temporal discretization schemes with multi-domain structural grids in the computational domain and a small time step are used to capture the unsteady flow physics and pressure fluctuation on the wall of volute casing. The solution to the inhomogeneous wave equation is expressed in the fiequency domain by making use of the fast Fourier transform and the acoustic far field, taking into account the scattering effect of volute casing, is computed using an acoustic thin-body boundary-element method. The calculated tonal sound pressure levels (SPLs) are compared with the experimental data. The calculated results accord well with the experimental data at blade-passing frequency (BPF) and its second harmonic, but are unsatisfactory at the higher frequency components. Finally, the free, scattering, and total acoustic fields in the volute casing are compared at BPF, and its fifth and tenth harmonic. The result shows that the scattering of the volute casing has an obvious effect on sound propagation with the increase in sound frequency.