Sound Radiation from a Subsonic Turbulent Plane Jet

Hu, Zheng; Morfey, C. L.

doi:10.2514/6.2002-2421

Cited by 3 publications

(4 citation statements)

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“…Large-scale structures, instability waves and sound radiation An example of a direct computation of sound is given on figure 1. This shows vorticity (inner region) and dilatation rate (outer region) for a Mach 0.9 plane jet at Reynolds number 2000 (based on jet width), computed using the method of Hu, Morfey & Sandham (2002). The sound field emanates from a region of the flow (centred around x = 5 jet widths) that is dominated by large-scale organized structures.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear mechanisms of sound generation in a perturbed parallel jet flow

Sandham

Morfey

2006

J. Fluid Mech.

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An initial value problem with relevance to jet noise is investigated. A plane parallel jet flow is subjected to a spatially localized initial disturbance and is then left to evolve according to the two-dimensional compressible Navier-Stokes equations. The hydrodynamic response is in the form of a convecting vortex packet. The Ffowcs WilliamsHawkings approach is formulated in the time domain and used to extrapolate from the simulated near field to the acoustic far field. The predominant downstream sound radiation comes from an early stage of nonlinear development of the vortex packet. Two simplified models to account for the radiation are introduced, based on nonlinear mode interactions on a prescribed base flow. The first uses two sets of linearized Euler equations, coupled via the inviscid Lilley-Goldstein acoustic analogy. This formulation separates the linear sound field from the sound field driven by nonlinear interactions; qualitative agreement of the latter with the Navier-Stokes computations demonstrates the importance of nonlinear interactions. The second model uses combinations of linear inviscid eigenmodes to drive the sound field, which allows extraction of the dominant mode interactions responsible for the observed radiation pattern. The results indicate that a difference-wavenumber nonlinear interaction mechanism dominates sound radiation from subsonic instability modes in shear flows.

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Section: Introductionmentioning

confidence: 99%

Nonlinear mechanisms of sound generation in a perturbed parallel jet flow

Sandham

Morfey

2006

J. Fluid Mech.

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“…34,53 A stationary or translating point source have been used by Lyrintzis et al, 34,53 Myers & Hausmann, 31 and Lockard 54 and a rotating point source by Lyrintzis et al 64 and Berezin et al 89 Exponential source distributions have been used by Pilon and Lyrintzis. 35,43,44,46 Hu et al 90 used a line monopole source and a Gaussian pressure and vorticity pulse (category 3 benchmark problem 91 ) to verify their two-dimensional FW-H formulation. Farassat and Farris 33 used dipole distributions on a flat surface and a sphere to validate the supersonic formulation (i.e.…”

Section: Validation Resultsmentioning

confidence: 99%

“…The uses of FW-H method in jet noise have been sparse. Morris et al 135,136 and Uzun et al 137 used the method with good results and Hu et al, 90,138 used a two-dimensional formulation of the porous FW-H equation to evaluate noise radiation from a plane jet. Rahier et al 139 compared the methods for numerical acoustic predictions for hot jets.…”

Section: Jet Noisementioning

confidence: 99%

Surface Integral Methods in Computational Aeroacoustics—From the (CFD) Near-Field to the (Acoustic) Far-Field

Lyrintzis¹

2003

International Journal of Aeroacoustics

237

124

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A review of recent advances in the use of surface integral methods in Computational AeroAcoustics (CAA) for the extension of near-field CFD results to the acoustic far-field is given. These integral formulations (i.e. Kirchhoff's method, permeable (porous) surface Ffowcs-Williams Hawkings (FW-H) equation) allow the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the far-field sound, instead of the volume integrals required by the traditional acoustic analogy method (i.e. Lighthill, rigid body FW-H equation). A numerical CFD method is used for the evaluation of the flow-field solution in the near field and thus on the control surface. Diffusion and dispersion errors associated with wave propagation in the far-field are avoided. The surface integrals and the first derivatives needed can be easily evaluated from the near-field CFD data. Both methods can be extended in order to include refraction effects outside the control surface. The methods have been applied to helicopter noise, jet noise, propeller noise, ducted fan noise, etc. A simple set of portable Kirchhoff/FW-H subroutines can be developed to calculate the far-field noise from inputs supplied by any aerodynamic near/mid-field CFD code.

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“…To minimize reflection from the computational boundaries, fringe zones are put along the inflow and outflow boundaries with exponential damping functions applied. Details of the numerical method used can be found in Hu et al [15,16] .…”

Section: Numerical Approachmentioning

confidence: 99%

Evaluation of Acoustic Sources in an Excited Unstable Laminar Shear Layer

Morfey

Sandham

2006

International Journal of Aeroacoustics

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The radiation of sound from artificial sources in a developing shear layer is studied numerically, in order to address an issue that arises in acoustic analogy models of jet noise: namely whether the unstable response of the mean-flow shear layer has a significant effect on sound radiation. Direct numerical simulation of a forced two-dimensional compressible laminar mixing layer has been carried out at a Reynolds number of 250, based on the mixing layer initial vorticity thickness and the upper free-stream velocity. The free-stream Mach numbers of the mixing layer are 0.9 and 0.45. The flow is excited with a single-frequency body force field that is acoustically compact and is derived from an applied-stress distribution. Sound radiation from the mixing layer is calculated at the forcing frequency, and compared with radiation from a uniform flow under the same forcing. Comparisons are shown for the most-unstable forcing frequency over a wide amplitude range. The pressure radiated on either side of the mixing layer differs very little from that radiated into a uniform flow of the same Mach number under the same forcing, although the higher forcing amplitudes used are sufficient to trigger the non-linear process of vortex roll-up in the case of the mixing layer. The dominant source position for the radiated pressure at the forcing frequency is estimated via a wavenumber-frequency domain analysis. It is found to be close to the location of the applied forcing, with little contribution from mixing-layer vortical structures that develop downstream.

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Sound Radiation from a Subsonic Turbulent Plane Jet

Cited by 3 publications

References 0 publications

Nonlinear mechanisms of sound generation in a perturbed parallel jet flow

Nonlinear mechanisms of sound generation in a perturbed parallel jet flow

Surface Integral Methods in Computational Aeroacoustics—From the (CFD) Near-Field to the (Acoustic) Far-Field

Evaluation of Acoustic Sources in an Excited Unstable Laminar Shear Layer

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