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Research Papers

Fan Noise Control Using Microperforated Splitter Silencers

[+] Author and Article Information
Sabry Allam

Automotive Technology Department,
Faculty of Industrial Education,
Helwan University,
Elsawah Street, Elkoba,
Cairo 11282, Egypt

Mats Åbom

KTH-Competence Centre for
Gas Exchange (CCGEx),
The Marcus Wallenberg Laboratory (MWL),
Stockholm SE-100 44, Sweden

Contributed by the Noise Control and Acoustics Division of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received August 27, 2013; final manuscript received March 5, 2014; published online April 15, 2014. Assoc. Editor: Sheryl M. Grace.

J. Vib. Acoust 136(3), 031017 (Apr 15, 2014) (8 pages) Paper No: VIB-13-1298; doi: 10.1115/1.4027245 History: Received August 27, 2013; Revised March 05, 2014

Splitter or baffle silencers are commonly used, for example, in heating ventilation and air conditioning (HVAC) systems and as inlet/outlet silencers on gas turbines. Another application is to reduce noise from the cooling fan inlet for large IC-engines. A splitter silencer can be seen as a periodic arrangement of parallel rectangular absorbers, which can be placed in a rectangular duct. The noise reduction afforded by parallel splitters depends not only on the physical properties of the lining but also upon the angle of incidence of the impinging sound waves, and the splitter and duct dimensions. In this paper, the potential of using splitters made of microperforated plates (MPPs) is investigated, with a particular focus on cooling fan inlet/outlet applications.

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Figures

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Fig. 1

The structure of a parallel splitters silencer: air channel width H = 2a, splitter thickness 2d

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Fig. 2

Structure of a MPP splitter with inner walls. The splitter main surfaces are made of MPP but the outer sides (edges) are solid, see also Fig. 4. The inner walls forming rectangular cells can be either solid or made of MPP. (a) Photo of the MPP used with slits (AcustimetTM). (b) MPP splitter with inner walls.

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Fig. 3

Geometry of two splitters or baffles in a rectangular duct. Note only one period of the air/splitter system along x is considered, see Fig. 1.

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Fig. 4

Details of the MPP splitter or baffle. Note front and back is made of MPP but the outer sides (splitter edges) are assumed to be solid. The inner walls can either be solid or made from the same MPP as the front/back.

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Fig. 5

Solution of eigenvalue Km* for modes (m,0) for a set of given parametric values, H = 0.055 m, d = 0.025 m, W = 1 m, L = 0.5 m, f ( = 0–10,000 Hz clockwise direction), and M = 0

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Fig. 6

Effect of varying the mode order n in the y-direction on the eigenvalue Km* for a set of given parametric values, H = 0.055 m, d = 0.025 m, W = 1 m, L = 0.5 m, and f (= 0–10,000 Hz clockwise direction)

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Fig. 7

Sound attenuation for different modes (0,n) for a set of given parametric values, H = 0.055 m, d = 0.025 m, W = 1 m, L = 0.5 m, and f ( = 0–10,000 Hz)

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Fig. 8

Sound attenuation for different modes (m,0) for a set of given parametric values, H = 0.055 m, d = 0.025 m, W = 1 m, L = 0.5 m, and f ( = 0–10,000 Hz)

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Fig. 9

Measurement setup used with the ISO Standard (15186) procedure. The silencer is mounted in a wall between two rooms and the incident and transmitted sound powers are measured in one-third octave bands.

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Fig. 10

Effect of splitter interior design on the measured sound TL at M = 0. Ten parallel MPP splitters, H = 0.055 m, d = 0.025 m, W = 1 m, and L = 0.5 m.

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Fig. 11

Measured and calculated transmission loss in one-third octave bands. Ten parallel MPP splitters, H = 0.055 m, d = 0.025 m, W = 1 m, and L = 0.5 m. (a) TL versus frequency for the no flow case. (b) Effect of flow on TL.

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Fig. 12

Measured and calculated transmission loss at M = 0. Ten parallel splitters, H = 0.055 m, d = 0.025 m, W = 1 m, and L = 0.5 m. (a) FEM mesh covering one period of the air/splitter periodic system. Mesh elements 239,045 and 385,294 degree of freedom. (b) TL versus frequency for different configurations at no flow case.

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Fig. 13

Calculated normalized impedance versus frequency for the used MPP with slits at M = 0, σ = 4%,t = 1 mm, anddMPP = 0.2 mm

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