Duct sound absorber

Patent metadata

Field	Value
Publication number	US-11114080-B2
Application number	US-201816113208-A
Country	US
Kind code	B2
Filing date	Aug 27, 2018
Priority date	Aug 27, 2018
Publication date	Sep 7, 2021
Grant date	Sep 7, 2021

Abstract

Sound absorption units for fluid ducts include two acoustically coupled pairs of Helmholtz resonators. The two resonators within each pair have identical resonance frequency, however the upstream resonator within each pair is partly filled with an acoustically lossy porous material, so that the upstream resonator within each pair has greater acoustic loss than its coupled downstream resonator. The upstream pair of resonators has a relatively low resonance frequency, while the downstream pair of resonators has a relatively high resonance frequency. The combination of frequency mismatch between the resonator pairs, and loss mismatch within each resonator pair, produces consistently high sound absorption across a broad frequency spectrum.

First claim

What is claimed is:

1. A fluid duct sound absorption system comprising:
a duct having at least one side wall for directing flow of a fluid and having a longitudinal axis defining upstream and downstream directions; and
a low frequency (LF) coupled pair of Helmholtz resonators comprising an upstream LF Helmholtz resonator and a downstream LF Helmholtz resonator separated by a first coupling distance, each of the upstream LF Helmholtz resonator and the downstream LF Helmholtz resonator comprising:
a LF chamber portion bounded by at least one enclosure wall defining a LF chamber volume; and
a LF neck connecting an aperture in the at least one enclosure wall to an aperture in the at least one side wall and thereby placing the LF chamber portion in fluid communication with the duct; and

a high frequency (HF) coupled pair of Helmholtz resonators positioned downstream from the LF coupled pair of Helmholtz resonators, and comprising an upstream HF Helmholtz resonator and a downstream HF Helmholtz resonator separated by a second coupling distance, each of the upstream HF Helmholtz resonator and the downstream HF Helmholtz resonator comprising:
a HF chamber portion bounded by at least one enclosure wall defining a HF chamber volume; and
a HF neck connecting an aperture in the at least one enclosure wall to an aperture in the at least one side wall and thereby placing the HF chamber portion in fluid communication with the duct,
the LF neck of the upstream LF Helmholtz resonator and the HF neck of the upstream HF Helmholtz resonator being covered and at least partially filled with an acoustically absorbing medium.

2. The fluid duct sound absorption system as recited in claim 1 , wherein the first coupling distance is defined by an equation

s
1

≅

0.2
⁢

(

c

f
L

)

wherein s 1 is the first coupling distance, c, is the speed of sound in the fluid; and f L is a resonance frequency of each of the upstream LF Helmholtz resonator and the downstream LF Helmholtz resonator.

3. The fluid duct sound absorption system as recited in claim 1 , wherein the second coupling distance is defined by an equation

s
2

≅

0.2
⁢

(

c

f
H

)

wherein s 2 is the second coupling distance, c, is the speed of sound in the fluid; and f H is a resonance frequency of each of the upstream HF Helmholtz resonator and the downstream HF Helmholtz resonator.

4. The fluid duct sound absorption system as recited in claim 1 , wherein duct defines a distance, D, between an aperture in the at least one side wall at which a neck connects, and an opposing point in the at least one side wall, according to an equation:

D
<

0.5
⁢

⁢

c

f
H

wherein c is the speed of sound in the fluid and f H is a resonance frequency of each of the upstream HF Helmholtz resonator and the downstream HF Helmholtz resonator.

5. The fluid duct sound absorption system as recited in claim 1 , wherein the duct has at least two LF coupled pairs of Helmholtz resonators positioned in parallel with one another, and at least two HF coupled pairs of Helmholtz resonators positioned in parallel with one another.

6. The fluid duct sound absorption system as recited in claim 1 , wherein the upstream LF Helmholtz resonator and the downstream LF Helmholtz resonator each has a first longitudinal axis and a second longitudinal axis forming a nonlinear angle with the first longitudinal axis, such that the LF chamber portion protrudes from the at least one side wall at the nonlinear angle.

7. The fluid duct sound absorption system as recited in claim 6 , wherein the second longitudinal axis is curvilinear, such that the upstream LF Helmholtz resonator and the downstream LF Helmholtz resonator at least partially wrap around the duct.

8. The fluid duct sound absorption system as recited in claim 1 , comprising an interpair distance of separation, d, measured from midpoints of the LF and HF coupled Helmholtz resonator pairs, according to an equation:

d
>

(

s
1

+

s
2

+

w
1

+

w
2

)

2

wherein s 1 and s 2 are the first and second coupling distances; w 1 is a width of the LF chamber portion of a LF Helmholtz resonator; and w 2 is a width of the HF chamber portion of a HF Helmholtz resonator.

9. A fluid duct sound absorption system comprising:
a duct having at least one side wall for directing flow of a fluid and having a longitudinal axis defining upstream and downstream directions; and
a low frequency (LF) coupled pair of Helmholtz resonators comprising an upstream LF Helmholtz resonator and a downstream LF Helmholtz resonator positioned on the duct and separated by a first coupling distance, each of the upstream LF Helmholtz resonator and the downstream LF Helmholtz resonator having a first resonance frequency;
a high frequency (HF) coupled pair of Helmholtz resonators positioned downstream from the LF coupled pair of Helmholtz resonators comprising an upstream HF Helmholtz resonator and a downstream HF Helmholtz resonator positioned on the duct and separated by a second coupling distance, each of the upstream HF Helmholtz resonator and the downstream HF Helmholtz resonator having a second resonance frequency that is greater than the first resonance frequency; and
an internal sound reflector formed of a planar acoustically reflective material positioned inside the duct to reflect sound waves emanating from any of the Helmholtz resonators back to the same Helmholtz resonator,
the upstream LF Helmholtz resonator and the upstream HF Helmholtz resonator being covered and at least partially filled with an acoustically absorbing medium.

10. The fluid duct sound absorption system as recited in claim 9 , wherein the first coupling distance is defined by an equation

Assignees

• Toyota Eng & Mfg North America

Inventors

• Lee Taehwa
• Iizuka Hideo

Classifications

• G10K11/161 Primary

  in systems with fluid flow (G10K11/162 takes precedence; gas flow silencers or exhaust apparatus for machines or engines in general or for internal combustion engine F01N, noise absorbers in pipes or pipe systems F16L55/02; noise absorption in air conditioning and ventilation F24F13/24; silencing exhaust or propulsion jets in aircraft B64D33/06) · CPC title

• G10K11/162

  Selection of materials · CPC title

• G10K11/172 Primary

  using resonance effects · CPC title

• B60H1/00564

  of air ducts · CPC title

• B60H2001/006

  Noise reduction · CPC title