Aerodynamic and Acoustic Performance of a Single Stage Axial Fan With Extensive Blade Sweep Designed to Limit Noise Emissions

Abstract

Not only the aerodynamic performance of axial flow fans is important but also the acoustic behaviour plays a vital role. It is to be expected that in the future noise limits will be more regulated by legislation. The aim of this project is to develop a very versatile tool for efficient and noise reduced axial flow fans in rotor / stator configuration. This paper describes the design, numerical verification and tests of a highly loaded single stage axial flow fan making use of extensive blade sweep in rotor and stator for acoustic reasons. The tests include aerodynamic and acoustic investigations. The stage is a conventional free vortex design with unconventional blades of a special planform. The blade sections of both rotor and stator are NACA 65-sections on circular arc mean lines. Sectional diffusion factors and de Haller numbers are close to their respective limits, especially for the sections next to the rotor and stator hubs. The rotor is characterised by a forward-swept leading edge with increasing sweep angle towards hub and tip and an unswept trailing edge. The leading edge of the stator blades is forward-swept as before but this time at an almost constant sweep angle between the hub and the two-thirds position of the blade span. The trailing edge is straightened for reducing the previously mentioned aerodynamic loadings. The study shows that the numerical results are consistent with the experimental outcome. It concludes that the advanced design features show potential aerodynamic and acoustic benefits by sweeping the blade in the described manner. This is particularly the case when comparing to single row designs.