Use of downstream fluid injection to reduce subsonic jet noise

Pankaj Rajput, Sunil Kumar

Research output: Contribution to journalArticle

Abstract

A fluid injection scheme consisting of multiple radial microjets located downstream from the nozzle exhaust is analyzed for its ability to suppress far field jet noise. Microjets in cross flow are known to enhance turbulent mixing due to the induced stream-wise vortices. Contrary to previous studies which injected fluid either inside the nozzle or just at the nozzle exhaust, this injection scheme uses a coaxial injector tube to inject multiple equally spaced microjets perpendicular to the jet axis at an axial location downstream from the nozzle exhaust. Microjet injection closer to the jet axis leads to the formation of a counter rotating vortex pair (CVP) close to the injection location which further beaks down into stream-wise vortices as the microjet bends and follows the flow direction. Detailed Large Eddy Simulations are performed for a nozzle-injector setup operating at Mach 0.9 jet with Reynolds number ≈106 to help understand the aerodynamic and acoustic features of the interaction of this fluid injection scheme with the main jet. Permeable Ffowcs Willaims Hawkings based formulation is used for computing the far field acoustic spectra for injector setups with various numbers of injection ports (np) at two microphone locations. It is observed that as the number of microjets is increased, it leads to reduction in the far field noise. Peak noise reduction of ≈ 4.5 dB is observed for both locations. However, beyond np > 4 there is a lower acoustic benefit per additional port due to spatial interference between the induced CVPs.

Original languageEnglish (US)
Pages (from-to)554-574
Number of pages21
JournalInternational Journal of Aeroacoustics
Volume18
Issue number4-5
DOIs
StatePublished - Jul 1 2019

Fingerprint

fluid injection
jet aircraft noise
exhaust nozzles
Nozzles
injectors
injection
far fields
Fluids
vortices
Vortex flow
nozzles
acoustics
Acoustics
turbulent mixing
cross flow
large eddy simulation
microphones
noise reduction
aerodynamics
Acoustic fields

Keywords

  • computational aeroacoustics
  • fluid injection
  • Jet noise
  • large Eddy simulation
  • OpenFOAM

ASJC Scopus subject areas

  • Aerospace Engineering
  • Acoustics and Ultrasonics

Cite this

Use of downstream fluid injection to reduce subsonic jet noise. / Rajput, Pankaj; Kumar, Sunil.

In: International Journal of Aeroacoustics, Vol. 18, No. 4-5, 01.07.2019, p. 554-574.

Research output: Contribution to journalArticle

@article{ef70ddf67e9945b18694b2d71653ad27,
title = "Use of downstream fluid injection to reduce subsonic jet noise",
abstract = "A fluid injection scheme consisting of multiple radial microjets located downstream from the nozzle exhaust is analyzed for its ability to suppress far field jet noise. Microjets in cross flow are known to enhance turbulent mixing due to the induced stream-wise vortices. Contrary to previous studies which injected fluid either inside the nozzle or just at the nozzle exhaust, this injection scheme uses a coaxial injector tube to inject multiple equally spaced microjets perpendicular to the jet axis at an axial location downstream from the nozzle exhaust. Microjet injection closer to the jet axis leads to the formation of a counter rotating vortex pair (CVP) close to the injection location which further beaks down into stream-wise vortices as the microjet bends and follows the flow direction. Detailed Large Eddy Simulations are performed for a nozzle-injector setup operating at Mach 0.9 jet with Reynolds number ≈106 to help understand the aerodynamic and acoustic features of the interaction of this fluid injection scheme with the main jet. Permeable Ffowcs Willaims Hawkings based formulation is used for computing the far field acoustic spectra for injector setups with various numbers of injection ports (np) at two microphone locations. It is observed that as the number of microjets is increased, it leads to reduction in the far field noise. Peak noise reduction of ≈ 4.5 dB is observed for both locations. However, beyond np > 4 there is a lower acoustic benefit per additional port due to spatial interference between the induced CVPs.",
keywords = "computational aeroacoustics, fluid injection, Jet noise, large Eddy simulation, OpenFOAM",
author = "Pankaj Rajput and Sunil Kumar",
year = "2019",
month = "7",
day = "1",
doi = "10.1177/1475472X19859890",
language = "English (US)",
volume = "18",
pages = "554--574",
journal = "International Journal of Aeroacoustics",
issn = "1475-472X",
publisher = "Multi-Science Publishing Co. Ltd",
number = "4-5",

}

TY - JOUR

T1 - Use of downstream fluid injection to reduce subsonic jet noise

AU - Rajput, Pankaj

AU - Kumar, Sunil

PY - 2019/7/1

Y1 - 2019/7/1

N2 - A fluid injection scheme consisting of multiple radial microjets located downstream from the nozzle exhaust is analyzed for its ability to suppress far field jet noise. Microjets in cross flow are known to enhance turbulent mixing due to the induced stream-wise vortices. Contrary to previous studies which injected fluid either inside the nozzle or just at the nozzle exhaust, this injection scheme uses a coaxial injector tube to inject multiple equally spaced microjets perpendicular to the jet axis at an axial location downstream from the nozzle exhaust. Microjet injection closer to the jet axis leads to the formation of a counter rotating vortex pair (CVP) close to the injection location which further beaks down into stream-wise vortices as the microjet bends and follows the flow direction. Detailed Large Eddy Simulations are performed for a nozzle-injector setup operating at Mach 0.9 jet with Reynolds number ≈106 to help understand the aerodynamic and acoustic features of the interaction of this fluid injection scheme with the main jet. Permeable Ffowcs Willaims Hawkings based formulation is used for computing the far field acoustic spectra for injector setups with various numbers of injection ports (np) at two microphone locations. It is observed that as the number of microjets is increased, it leads to reduction in the far field noise. Peak noise reduction of ≈ 4.5 dB is observed for both locations. However, beyond np > 4 there is a lower acoustic benefit per additional port due to spatial interference between the induced CVPs.

AB - A fluid injection scheme consisting of multiple radial microjets located downstream from the nozzle exhaust is analyzed for its ability to suppress far field jet noise. Microjets in cross flow are known to enhance turbulent mixing due to the induced stream-wise vortices. Contrary to previous studies which injected fluid either inside the nozzle or just at the nozzle exhaust, this injection scheme uses a coaxial injector tube to inject multiple equally spaced microjets perpendicular to the jet axis at an axial location downstream from the nozzle exhaust. Microjet injection closer to the jet axis leads to the formation of a counter rotating vortex pair (CVP) close to the injection location which further beaks down into stream-wise vortices as the microjet bends and follows the flow direction. Detailed Large Eddy Simulations are performed for a nozzle-injector setup operating at Mach 0.9 jet with Reynolds number ≈106 to help understand the aerodynamic and acoustic features of the interaction of this fluid injection scheme with the main jet. Permeable Ffowcs Willaims Hawkings based formulation is used for computing the far field acoustic spectra for injector setups with various numbers of injection ports (np) at two microphone locations. It is observed that as the number of microjets is increased, it leads to reduction in the far field noise. Peak noise reduction of ≈ 4.5 dB is observed for both locations. However, beyond np > 4 there is a lower acoustic benefit per additional port due to spatial interference between the induced CVPs.

KW - computational aeroacoustics

KW - fluid injection

KW - Jet noise

KW - large Eddy simulation

KW - OpenFOAM

UR - http://www.scopus.com/inward/record.url?scp=85069635674&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85069635674&partnerID=8YFLogxK

U2 - 10.1177/1475472X19859890

DO - 10.1177/1475472X19859890

M3 - Article

VL - 18

SP - 554

EP - 574

JO - International Journal of Aeroacoustics

JF - International Journal of Aeroacoustics

SN - 1475-472X

IS - 4-5

ER -