Large eddy simulation on aerodynamic noise mechanism of variable-pitch axial fan

This paper deeply discusses the differences between the internal flow and noise generation mechanism of the variable-pitch axial fan caused by the existence of the rotor root gap and that of the traditional fan from three aspects: internal flow, aerodynamic noise source, and flow-noise synergy. The numerical results show that the third-generation vortex identification method can identify blade root vortex V1 and blade root gap vortex V2 that are not found in traditional rotating machinery, as well as their impact on the stator hub to produce V5, a rotor–stator interaction that cannot be ignored. The distribution of time derivative of pressure and Lamb vector shows that the noise mechanism of the variable-pitch axial fan also includes the interference of V1 with the hub and adjacent rotors during the development process, in addition to the above interference and the tip leakage vortex V4 and stator interference that exist in traditional fan outside. The new flow interference effects and corresponding noise mechanisms within the variable-pitch axial fan are elaborated upon, revealing characteristics that are entirely distinct from those of the traditional fan. Finally, the synergistic relationship between flow velocity and acoustic pressure is examined to elucidate the connection between the flow field and the radiated noise.