### Abstract

Original language | English |
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Publication status | Published - 26 Nov 2019 |

Event | 72nd Annual Meeting of the APS Division of Fluid Dynamics : Division of Fluid Dynamics - Washington State Convention Center, Seattle, United States Duration: 23 Nov 2019 → 26 Nov 2019 https://www.apsdfd2019.org/ |

### Conference

Conference | 72nd Annual Meeting of the APS Division of Fluid Dynamics |
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Abbreviated title | APS-DFD |

Country | United States |

City | Seattle |

Period | 23/11/19 → 26/11/19 |

Internet address |

### Fingerprint

### Keywords

- jet noise
- acoustic analogies
- applied mathematics

### Cite this

*Analysing the structure of the acoustic analogy based-high frequency Green’s function in non-axi-symmetric sheared flows via a Ray tracing solver*. Abstract from 72nd Annual Meeting of the APS Division of Fluid Dynamics , Seattle, United States.

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**Analysing the structure of the acoustic analogy based-high frequency Green’s function in non-axi-symmetric sheared flows via a Ray tracing solver.** / Stirrat, Sarah; Afsar, Mohammed; Sescu, Adrian.

Research output: Contribution to conference › Abstract

TY - CONF

T1 - Analysing the structure of the acoustic analogy based-high frequency Green’s function in non-axi-symmetric sheared flows via a Ray tracing solver

AU - Stirrat, Sarah

AU - Afsar, Mohammed

AU - Sescu, Adrian

PY - 2019/11/26

Y1 - 2019/11/26

N2 - The chevron nozzle remains a popular approach aimed at reducing jet noise. It works by breaking up large turbulence structures and by increasing mixing, but it also effects propagation of sound. In this study, we investigate the effect of chevron-type mean flow in an acoustic analogy model where the wave propagation reduces to the solution of the Rayleigh equation and is calculated using a ray theory model for a jet represented by a transversely sheared mean flow. Since the generalised acoustic analogy (GAA) shows that the acoustic pressure is given by the convolution product of a rank-2 tensor propagator and the fluctuating Reynolds Stress, we determine the propagator (that is related to the vector adjoint Green's function of the linearised Euler operator) using the high frequency Ray theory developed by Goldstein (J. S. V., Vol. 80, p. 499, 1982) under an isotropic model of the fluctuating Reynolds stress. We calculate the Rayleigh equation Green’s function at high frequencies for a series of chevron mean flow patterns with multiple lobes. Our results reveal that the chevron jet introduces much more non-periodic spatial modulation of the Green’s function with a local minima in amplitude within the jet. We conclude by discussing how this explains the observed reduction in sound.

AB - The chevron nozzle remains a popular approach aimed at reducing jet noise. It works by breaking up large turbulence structures and by increasing mixing, but it also effects propagation of sound. In this study, we investigate the effect of chevron-type mean flow in an acoustic analogy model where the wave propagation reduces to the solution of the Rayleigh equation and is calculated using a ray theory model for a jet represented by a transversely sheared mean flow. Since the generalised acoustic analogy (GAA) shows that the acoustic pressure is given by the convolution product of a rank-2 tensor propagator and the fluctuating Reynolds Stress, we determine the propagator (that is related to the vector adjoint Green's function of the linearised Euler operator) using the high frequency Ray theory developed by Goldstein (J. S. V., Vol. 80, p. 499, 1982) under an isotropic model of the fluctuating Reynolds stress. We calculate the Rayleigh equation Green’s function at high frequencies for a series of chevron mean flow patterns with multiple lobes. Our results reveal that the chevron jet introduces much more non-periodic spatial modulation of the Green’s function with a local minima in amplitude within the jet. We conclude by discussing how this explains the observed reduction in sound.

KW - jet noise

KW - acoustic analogies

KW - applied mathematics

UR - https://www.apsdfd2019.org/

UR - http://meetings.aps.org/Meeting/DFD19/Session/Q06.6

M3 - Abstract

ER -