Measurements compared to analytical prediction of the sound emitted by a high-speed fan stage

Acoustic measurements have been performed to characterize the noise emission of a high-speed low-pressure-ratio fan stage at various operating conditions. In parallel, simulations of different tonal and broadband noise sources have been carried out based on an analytical prediction tool. Due to the presumably unclean inflow conditions of the fan, the experimental results do not allow to conclude clearly about the dominant broadband mechanism and show a strong tone at the first blade passing frequency harmonics despite the cut-off design of the fan. Still, comparisons of the tone levels are good and the analytical models provide indications about the different behaviour of each source as fan speed and fan loading are varied. The aerodynamic excitation pressure is introduced as a helpful quantity to understand the variations of broadband noise. An extension of the broadband excitation model is proposed to account for the interaction of stretched eddies with the rotor.

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