Abstract: Addressing the transmitted sound issue induced by four-bladed fans in top-discharge type air conditioner outdoor units, employs a combined approach of experimental testing and numerical simulation to systematically reveal the underlying vibro-acoustic coupling mechanism. Research demonstrates that system resonance originates from the coupling effect between the aerodynamic loads of the rotating fan and the structural natural frequencies. Based on this vibro-acoustic coupling mechanism analysis, a comprehensive noise reduction solution is proposed: suppressing resonant deformation modes of the fan blades through blade reinforcement, and dissipating vibrational energy using an arch-shaped bracket structure. Experimental validation confirms that the optimized design achieves a reduction exceeding 20 dB(A) in transmitted sound peak levels and a flow rate increase exceeding 1% across all fan speed settings. This study provides a novel engineering solution for flow-induced vibration and noise control in rotating machinery.

Key words: Four-bladed fans, Transmitted sound, Resonance