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Leakage Noise and Related Flow Pattern in a Low-Speed Axial Fan with Rotating Shroud

DIME-Dipartimento di Ingegneria meccanica, energetica, gestionale e dei trasporti, Università di Genova, via Montallegro, 1, I-16145 Genova, Italy
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This paper is an extended version of our paper in Proceedings of the 13th European Turbomachinery Conference on Fluid Dynamics & Thermodynamics ETC13, Lausanne, Switzerland, 8–12 April 2019. Paper No. 368.
Int. J. Turbomach. Propuls. Power 2019, 4(3), 17; https://doi.org/10.3390/ijtpp4030017
Received: 14 May 2019 / Accepted: 2 July 2019 / Published: 10 July 2019
The effect of rotational speed and pressure rise on the leakage flow noise radiated by a low-speed axial fan, provided with rotating shroud, has been systematically investigated. The flow in the gap region has been studied by means of particle image velocimetry (PIV) measurements taken in the meridional plane. At low blade loading, the leakage flow is restrained close to the rotor ring and, at higher loading, it forms a wide recirculation zone. In the latter conditions, an unsteady flow separation likely takes place in the blade tip region which may be observed in the instantaneous flow field only. The leakage flow noise generally increases with the blade loading, but is non-monotonic, as the overall sound pressure level (OASPL) growth is interrupted by local minima; such a trend is qualitatively independent of the rotational speed. As the loading increases, the sound pressure level (SPL) spectrum shows important modifications, since the characteristic frequency of the subharmonic narrowband humps related to the leakage noise decreases; furthermore, height and width of the humps vary non-monotonically. Such a complicated behavior is likely related to the modifications in the leakage flow pattern and also to the appearance of the flow separation at the blade tip. View Full-Text
Keywords: axial-flow fan; rotating shroud; ring rotor; stiff rotor; leakage flow; fan noise; subharmonic humps; PIV axial-flow fan; rotating shroud; ring rotor; stiff rotor; leakage flow; fan noise; subharmonic humps; PIV
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Canepa, E.; Cattanei, A.; Mazzocut Zecchin, F. Leakage Noise and Related Flow Pattern in a Low-Speed Axial Fan with Rotating Shroud. Int. J. Turbomach. Propuls. Power 2019, 4, 17.

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