Quantitative Estimate of Sound Attenuation of a Slit-like Duct Expansion Considering Sound Damping in It.

Journal of Sound and Vibration

2002

Section: It Equals 2qmentioning

confidence: 99%

“…This tendency seems to show an evidence of the in#uence of viscosity. We had presented a simple method to predict actual slit properties regarding the in#uence of viscosity by modelling the slit as a single-degree-of-freedom system including a damping term [17].…”

Section: Resonant Properties Of Extremely Short Chambersmentioning

confidence: 99%

Resonant Properties of Short Expansion Chambers in a Circular Duct: Including Extremely Short Cases and Asymmetric Mode Wave Incidence Cases

Journal of Sound and Vibration

2002

“…From a practical viewpoint, a short chamber is expected to be used as a muffler for peaky, discrete-frequency noise as produced by fans (3) . While such a chamber is easy to attach to a duct flange or a duct end when its axial length is short, an excessively short chamber does not have sufficient resonant effect (4) .…”

Section: Introductionmentioning

confidence: 99%

Resonant Properties of a Short Expansion Chamber Symmetrically Located on Opposite Sides of a Rectangular Duct

Tsubakishita

2007

JEE

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A short expansion chamber in a duct acts as a resonator type muffler. The properties of this type of chamber have already been studied in detail by the authors for circular duct-chambers. In this paper, short chambers are applied to rectangular ducts. These chambers consist of two rectangular branches located symmetrically on opposite sides of a rectangular duct. The transmission properties of plane waves through the chambers were examined experimentally. For a very short axial chamber length, the resonant frequency was determined in the same manner as for a side-branch muffler with open end correction. Though considered proportional to depth in circular chambers, it becomes constant in rectangular chambers with fixed axial length, regardless of chamber depth. When the chamber length is close to half of the chamber height (corresponding to the upper limit of resonator-type mufflers), the resonant frequency is close to, but in excess of, the cut-off frequency of the chamber's second resonant mode. The reason for this discrepancy becomes clearer subsequent to examination of the sound field contours calculated using the finite difference method.

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“…Their value becomes larger as l becomes shorter. This is caused by the insufficient resonance in the slit, which occurs because the influence of the viscous damping at the inlet and outlet walls of the expansion becomes too great to be neglected (see Sadamoto and Murakami, 1998). In our experience, this influence becomes negligible when l ≥ 5 mm.…”

Section: Figurementioning

confidence: 84%

“…We noticed this property and thought to construct a compact silencer that could be realized if the property were maintained so that the chamber length became very short. So we investigated the properties of a very short expansion chamber experimentally and analytically (Sadamoto et al, 1993;Sadamoto and Murakami, 1998).…”

mentioning

confidence: 99%

Reduction of Discrete‐Frequency Fan Noise Using Slitlike Expansion Chambers

International Journal of Rotating Machinery

2003

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