Experimental Investigations of the Aeroacoustic Interactions of Fan Blade Skew, Leading Edge Serrations and Inflow Turbulence

An experimental campaign was undertaken to assess the performance of axial fan blades under various conditions, including unskewed, forward-skewed, and backward-skewed fan blade configurations, all with and without leading-edge serrations. Tests were conducted under free inflow and grid generated disturbed inflow conditions, with the flow field and turbulence characteristics measured using 3D hot-wire anemometry. Suction-side sound radiation was evaluated using microphones in an anechoic chamber, while the rotating beamforming method aided in localizing sound sources. The results show that the best compromise between efficiency and low noise emission can be achieved with the forward-skewed fan blades. Although the leading-edge serrations can further reduce the sound radiation, especially in turbulent inflow, they also lead to a reduction in the aerodynamic efficiency of the fan. The positive acoustic effects of blade skew and leading edge serration are not directly superimposed, so the reduction in total sound pressure level of a unskewed fan with leading edge serration is greater than that of a forward-skewed fan. The reason for this non-direct superposition can be identified in the improved flow over the blade, which is caused by both modifications, but cannot be continuously increased when combined