End-plate for noise-by-flow control in axial fans

The paper presents a design procedure for anti-vortex endplates that are fitted to tip limited blades of the subsonic axial fans utilised in compact cooling units. The authors study the impact of tip leakage vortex bursting on the performance of the studied class of fans. The vortex breakdown occurs in the swirling flows at a blade’s tip, and is found to be a flow feature associated with the production of fan acoustic emissions. The link between aerodynamic flow features in the blade tip region and fan acoustic emissions is exploited through a design process that aims to control the blade tip flow with the specific objective of reducing fan acoustic emissions. This noise-by-flow flow control design process is implemented by reconfiguring the end-plate at the blade tip using a multiple-vortex-breakdown criterion for the design of the end-plates. The aerodynamic and acoustic performance of the newly conceived end-plate design has been assessed and is compared with the performance of a fan with blades fitted with base-line end-plate geometry. The assessment of aerodynamic and acoustic performance utilises both numerical simulations of the flow-field in the blade tip region plus an experimental assessment of fan aerodynamic and acoustic performance. The reported research verified the technical merit of the developed passive noise control strategy, demonstrating that the control of blade tip leakage flow can result in a reduction in blade tip flow generated noise.