Investigation of an Axial Fan : Blade Stress and Vibration Due to Aerodynamic Pressure Field and Centrifugal Effects

A 1.829m (6 ft) diameter industrial large flow-rate axial fan operated at 1770 rpm was studied experimentally in laboratory conditions. The flow characteristics on the fan blade surfaces were investigated by measuring the pressure distributions on the blade suction and pressure surfaces and the results were discussed by comparing with analytical formulations and CFD. Flow visualizations were also performed to validate the flow characteristics near the blade surface and it was demonstrated that the flow characteristics near the fan blade surface were dominated by the centrifugal force of the fan rotation which resulted in strong three-dimensional flows. The time-dependent pressure measurement showed that the pressure oscillations on the fan blade were significantly dominated by vortex shedding from the fan blades. It was further demonstrated that the pressure distributions during the fan start-up were highly unsteady, and the main frequency variation of the static pressure was much smaller than the fan rotational frequency. The time dependent pressure measurement when the fan operated at a constant speed showed that the magnitude of the blade pressure variation with time and the main variation frequency was much smaller than the fan rotational frequency. The pressure variations that were related to the vortex shedding were slightly smaller than the fan rotational frequency. The strain gages were used to measure the blade stress and the results were compared with FEA results.