Characterising the Aerodynamic and Aeroacoustic Performance for a Small Axial-Flow Fan

Abstract

This study aims to predict the unsteady aerodynamic performance 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 acoustic field. A dual-time approach and finite volume control method is applied for the unsteady solution 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 theory. The unsteady force is divided into thrust in the rotational axis direction and drag in the rotational direction for rotor and strut. It is demonstrated that the unsteady forces acting on rotor and strut are produced by the interaction between rotor and strut, and has close relationship with the rotor wake structure and 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 leaned angle of struts can gain about 4 dB reduction of overall sound power level compared to the smallest one.