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Research Papers

Passive Noise Reduction for a Contrarotating Fan

[+] Author and Article Information
Chen Wang

Laboratory of Aerodynamics and Acoustics,
HKU Zhejiang Institute of
Research and Innovation and
Department of Mechanical Engineering,
The University of Hong Kong,
Pokfulam, Hong Kong
e-mail: chadwong@hku.hk

Lixi Huang

Laboratory of Aerodynamics and Acoustics,
HKU Zhejiang Institute of
Research and Innovation and
Department of Mechanical Engineering,
The University of Hong Kong,
Pokfulam, Hong Kong
e-mail: lixi@hku.hk

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 30, 2014; final manuscript received August 6, 2014; published online September 30, 2014. Editor: Ronald Bunker.

J. Turbomach 137(3), 031007 (Sep 30, 2014) (10 pages) Paper No: TURBO-14-1189; doi: 10.1115/1.4028357 History: Received July 30, 2014; Revised August 06, 2014

There has been renewed interest in the contrarotating (CR) fan configuration in aviation and other applications where size and weight are important design factors. Contra-rotation recovers swirl energy compared with the single-rotor design, but this advantage is not fully harnessed due to, perhaps, the issue of noise. This study explores passive noise reduction for a small, axial-flow, CR fan with perforated trailing-edge for the upstream rotor and perforated leading-edge for the downstream rotor. The fan is designed with simple velocity triangle analyses, which are checked by 3D flow computations. The aerodynamic consequence and the acoustic benefit of such perforated blading are investigated experimentally. The results show that there is a reduction of total pressure compared with the baseline CR fan at the same rotating speeds, but this is easily compensated for by slightly raising the rotating speeds. A reduction of 6–7 dB in overall noise is achieved for the same aerodynamic output, although there is a moderate noise increase in the high frequency range of 12.5–15.0 kHz due to blade perforations. The effect of inter-rotor separation distance is also investigated for the baseline design. A clear critical distance exists below which the increased spacing shows clear acoustic benefits.

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References

Figures

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Fig. 1

CAD pictures of front (left) and rear (right) rotors

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Fig. 2

(a) Computational domain and (b) mesh details in the front rotor domain

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Fig. 3

Relative velocity vectors on blade surfaces

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Fig. 5

The characteristic curves of experiment and computation

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Fig. 6

General picture of rotor–rotor interaction

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Fig. 7

CAD pictures of perforated front rotor (top left), perforated rear rotor (top right), and a close-up of the perforated front rotor (bottom)

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Fig. 8

Contours of relative velocity magnitude (m/s) for axial positions of (a) Z = 2 mm, (b) Z = 4 mm, (c) Z = 9 mm, and (d) Z = 14 mm, Z = 0 being the trailing edge of the front rotor

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Fig. 9

Contours of relative velocity magnitude (m/s) for r = 40 mm, with mixing plane at 16 mm from the trailing edge of the front rotor

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Fig. 10

Variation of SPL with axial spacing

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Fig. 11

Spectra comparison of the side noise

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Fig. 12

Characteristic curves of baseline and perforated blades

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Fig. 13

Comparison of SPL directivity for baseline and perforated blades

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Fig. 14

Spectral comparison of baseline and perforated blades at 330 deg

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Fig. 15

SPL distribution in different frequency range

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