In the present paper the effect of the rotor stator axial gap on tonal noise generated by axial flow fans employed for automotive cooling systems is studied. A fan equipped with either a 18 vanes stator or a 3 struts one, positioned at several axial gaps, is tested in a hemi-anechoic chamber during rotational speed ramps. To analyze the acoustic pressure properties three different quantities have been employed: the velocity scaled SPL at the BPF harmonics, the phase of the acoustic pressure at the BPF harmonics and the propagation function obtained by means of the spectral decomposition. The useful properties of these quantities and their joint use are first analyzed. Then they are employed for two purposes: investigating propagation effects and source strength fluctuations and identifying contributions to tonal noise due to random sources (large scale inlet turbulent structures) and due to deterministic sources (aerodynamic rotor-stator interaction). The results of the study show that the stator causes unexpected propagation effects which affected the measured SPL. These effects depend on the axial gap and on the considered BPF harmonic and they also affect the feasibility of a SPL velocity scaling.

Experimental study of the effect of the rotor-stator gap variation on the tonal noise generated by low-speed axial fans

CANEPA, EDWARD;CATTANEI, ANDREA;MAZZOCUT ZECCHIN, FABIO;Gabriele Milanese;
2013

Abstract

In the present paper the effect of the rotor stator axial gap on tonal noise generated by axial flow fans employed for automotive cooling systems is studied. A fan equipped with either a 18 vanes stator or a 3 struts one, positioned at several axial gaps, is tested in a hemi-anechoic chamber during rotational speed ramps. To analyze the acoustic pressure properties three different quantities have been employed: the velocity scaled SPL at the BPF harmonics, the phase of the acoustic pressure at the BPF harmonics and the propagation function obtained by means of the spectral decomposition. The useful properties of these quantities and their joint use are first analyzed. Then they are employed for two purposes: investigating propagation effects and source strength fluctuations and identifying contributions to tonal noise due to random sources (large scale inlet turbulent structures) and due to deterministic sources (aerodynamic rotor-stator interaction). The results of the study show that the stator causes unexpected propagation effects which affected the measured SPL. These effects depend on the axial gap and on the considered BPF harmonic and they also affect the feasibility of a SPL velocity scaling.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11567/577925
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