Semi-empirical design guidelines for controlling the vibration and noise of low-speed axial fans due to profile vortex shedding

Authors

Gábor Daku - Department of Fluid Mechanics, Faculty of Mechanical Engineering, Budapest University of Technology and Economics, Budapest, Hungary
János Vad - Department of Fluid Mechanics, Faculty of Mechanical Engineering, Budapest University of Technology and Economics, Budapest, Hungary

Abstract

This paper presents an overview on unfavourable design cases for which low-speed axial flow fans may exhibit an increased risk of blade resonance due to profile vortex shedding. To set up a design example, a circular-arc-cambered plate of 8% relative curvature is investigated in approaches of  a) blade mechanics and b) aerodynamics. a) Modelling the fan blade as a cantilever beam, the eigenfrequency of a plate of arbitrary camber has been expressed. b) A new iterative blade design method has been developed for providing profile vortex shedding of spanwise constant frequency. Coupling the two approaches, cases for vortex-induced blade resonance have been set up. Opposing to this basis, design guidelines have been elaborated for avoiding such resonance. Opposing to approach b), guidelines have also been developed for moderating the annoyance due to vortex shedding noise.