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Acoustic attenuation by conical-cavity-backed conical liners with simultaneous bias–grazing flow.

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Title: Acoustic attenuation by conical-cavity-backed conical liners with simultaneous bias–grazing flow.
Authors: Jha, NK1 (AUTHOR), Vikram1 (AUTHOR), Sah, NK1 (AUTHOR), Hota, RN1 (AUTHOR) rnhota@iitism.ac.in
Source: Sādhanā: Academy Proceedings in Engineering Sciences. Jun2025, Vol. 50 Issue 2, p1-18. 18p.
Subjects: Absorption of sound, Absorption coefficients, Sound waves, Internal combustion engines, Gas turbines
Abstract: An acoustic liner is used in combustion ducts and aeroengine nacelles to reduce noise. In the afterburner of a high-thrust-producing gas turbine engine, an acoustic liner in the presence of a simultaneous grazing flow and a bias flow mitigates thermoacoustic instability, a phenomenon in which pressure oscillations from combustion interact with acoustic waves, leading to undesirable vibrations and increased tonal noise. Using an acoustic liner prevents the feedback loop between heat release and pressure fluctuations. In most applications, acoustic liners are cylindrical with uniform cross-sectional area. In an attempt to enhance sound absorption, this paper presents an experimental investigation into the acoustic attenuation characteristics of conical-cavity-backed conical perforated liners in the presence of simultaneous bias and grazing flows. Several combinations of cone angles of liners and cavities are designed and fabricated, and a parametric study of cone angles is conducted for the no-flow and combined grazing–bias flow cases. The acoustic attenuation ability of conical liners and cavities is compared with their cylindrical counterparts. The experimental setup involves subjecting liners to controlled bias and grazing flow conditions and measuring their acoustic performance using the impedance tube technique. Conical adapters are used for conical liners to match the impedance tube diameter. The sound absorption coefficient of cavity-backed liners is calculated using the ASTM two-load method. Numerical simulations are performed by solving linearized Navier–Stokes equations in the frequency domain using COMSOL Multiphysics. Sound absorption coefficients obtained numerically are then compared with those of experimental measurements. Experimental results demonstrate that conical lined ducts provide better sound absorption than cylindrical lined ducts at specific grazing and bias flow rates. [ABSTRACT FROM AUTHOR]
Copyright of Sādhanā: Academy Proceedings in Engineering Sciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Acoustic attenuation by conical-cavity-backed conical liners with simultaneous bias–grazing flow.
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  Data: <searchLink fieldCode="JN" term="%22Sādhanā%3A+Academy+Proceedings+in+Engineering+Sciences%22">Sādhanā: Academy Proceedings in Engineering Sciences</searchLink>. Jun2025, Vol. 50 Issue 2, p1-18. 18p.
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  Data: <searchLink fieldCode="DE" term="%22Absorption+of+sound%22">Absorption of sound</searchLink><br /><searchLink fieldCode="DE" term="%22Absorption+coefficients%22">Absorption coefficients</searchLink><br /><searchLink fieldCode="DE" term="%22Sound+waves%22">Sound waves</searchLink><br /><searchLink fieldCode="DE" term="%22Internal+combustion+engines%22">Internal combustion engines</searchLink><br /><searchLink fieldCode="DE" term="%22Gas+turbines%22">Gas turbines</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: An acoustic liner is used in combustion ducts and aeroengine nacelles to reduce noise. In the afterburner of a high-thrust-producing gas turbine engine, an acoustic liner in the presence of a simultaneous grazing flow and a bias flow mitigates thermoacoustic instability, a phenomenon in which pressure oscillations from combustion interact with acoustic waves, leading to undesirable vibrations and increased tonal noise. Using an acoustic liner prevents the feedback loop between heat release and pressure fluctuations. In most applications, acoustic liners are cylindrical with uniform cross-sectional area. In an attempt to enhance sound absorption, this paper presents an experimental investigation into the acoustic attenuation characteristics of conical-cavity-backed conical perforated liners in the presence of simultaneous bias and grazing flows. Several combinations of cone angles of liners and cavities are designed and fabricated, and a parametric study of cone angles is conducted for the no-flow and combined grazing–bias flow cases. The acoustic attenuation ability of conical liners and cavities is compared with their cylindrical counterparts. The experimental setup involves subjecting liners to controlled bias and grazing flow conditions and measuring their acoustic performance using the impedance tube technique. Conical adapters are used for conical liners to match the impedance tube diameter. The sound absorption coefficient of cavity-backed liners is calculated using the ASTM two-load method. Numerical simulations are performed by solving linearized Navier–Stokes equations in the frequency domain using COMSOL Multiphysics. Sound absorption coefficients obtained numerically are then compared with those of experimental measurements. Experimental results demonstrate that conical lined ducts provide better sound absorption than cylindrical lined ducts at specific grazing and bias flow rates. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Sādhanā: Academy Proceedings in Engineering Sciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1007/s12046-025-02699-w
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        Text: English
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      – SubjectFull: Absorption of sound
        Type: general
      – SubjectFull: Absorption coefficients
        Type: general
      – SubjectFull: Sound waves
        Type: general
      – SubjectFull: Internal combustion engines
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      – SubjectFull: Gas turbines
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      – TitleFull: Acoustic attenuation by conical-cavity-backed conical liners with simultaneous bias–grazing flow.
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            NameFull: Jha, NK
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            NameFull: Vikram
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            NameFull: Sah, NK
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            – D: 01
              M: 06
              Text: Jun2025
              Type: published
              Y: 2025
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