Computational study of aero- and acoustic performance of a small axial-flow fan

Abstract

This study aims to predict the overall aerodynamic performance, unsteady forces and the tonal noise radiation from a small axial flow fan. The computation is divided into two stages: (a) the computation of the unsteady flow field at design and off-design working conditions, and (b) detailed analysis of the acoustic field. A dual-time scheme for dealing with rotor-stator or wakestruts interactions in turbomachinery environments by introducing a pseudo-time to represent the time variation of source terms and the finite volume control method are applied for the unsteady solutions involving the whole flow passages of the axial flow fan, and the pressure rise against volume flow rate is obtained and shown to be in good agreement with experimental data. The interaction of the rotor wake and the downstream struts has been simulated by investigating the effects of source distribution over the whole blades. And the tonal noise is then predicted based on Lowson’s theory. The unsteady force is divided into thrust in the rotational axis direction and drag in the rotational direction for the rotor and struts. It is demonstrated that the unsteady forces acting on the rotor and struts are produced by the interaction between them, and has a close relationship with the rotor wake structure and the strut alignment. In the rotor near wake, both the viscous and potential flow is dominant not only to aerodynamic forces but also to interaction noise. The present study shows that the higher lean angle of struts can gain about 4 dB reduction of overall sound power level compared to the smallest one.