The Mechanism of the Impact of Rotor Clocking on Tonal Noise of Two-Stage Axial Flow Fan

Abstract

Abstract. Rotor clocking refers to the circumferential indexing of adjacent rotors, each with an equal number of blades, which impacts tonal noise propagation and the performance of a two-stage axial flow fan. To elucidate the mechanisms by which rotor clocking influences tonal noise in a two-stage axial flow fan, we construct a tonal noise cascade model under the influence of rotor clocking. Utilizing the theory of sound wave superposition, it is determined that the relative phase of sound waves can be controlled through rotor clocking to reduce the amplitude of tonal noise. Through numerical simulations, we visualize the internal flow variations across different rotor clocking models of the fan, investigating pressure fluctuation characteristics in both time and frequency domains, as well as the excitation force characteristics of the second-stage rotor. This study reveals the influence patterns of rotor clocking on flow-induced excitation in the rotor–stator interaction region. Furthermore, by adopting the proper orthogonal decomposition (POD) method, we conduct a quantitative assessment of the primary energy structures in the flow field, analyzing each mode's contribution to the field's energy. Finally, we establish a bridge between internal flow field variations and tonal noise amplitude from both the computational acoustics and acoustic testing perspectives. The research results indicate that the simulated noise spectrum aligns well with the experimental noise spectrum, with tonal noise sound pressure level amplitudes differing by up to approximately 5 dB across different fan rotor clocking models.