Jet noise from instability mode interactions

Sandham, Neil D.; Salgado, Adriana; Agarwal, Anurag

doi:10.2514/6.2008-2987

Cited by 8 publications

(5 citation statements)

References 19 publications

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“…The present model can be extended (Sandham et al 2008) to look at different source terms. Instead of introducing the forcing along the surface of a cylinder as done here, the various source terms on the r.h.s.…”

Section: Discussionmentioning

confidence: 99%

Nonlinear interaction model of subsonic jet noise

Sandham

Salgado

2008

Phil. Trans. R. Soc. A.

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Noise generation in a subsonic round jet is studied by a simplified model, in which nonlinear interactions of spatially evolving instability modes lead to the radiation of sound. The spatial mode evolution is computed using linear parabolized stability equations. Nonlinear interactions are found on a mode-by-mode basis and the sound radiation characteristics are determined by solution of the Lilley-Goldstein equation. Since mode interactions are computed explicitly, it is possible to find their relative importance for sound radiation. The method is applied to a single stream jet for which experimental data are available. The model gives Strouhal numbers of 0.45 for the most amplified waves in the jet and 0.19 for the dominant sound radiation. While in near field axisymmetric and the first azimuthal modes are both important, far-field sound is predominantly axisymmetric. These results are in close correspondence with experiment, suggesting that the simplified model is capturing at least some of the important mechanisms of subsonic jet noise.

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Section: Discussionmentioning

confidence: 99%

Nonlinear interaction model of subsonic jet noise

Sandham

Salgado

2008

Phil. Trans. R. Soc. A.

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“…From figures 20(a) and 20(b), we can immediately observe that using linearly calculated source terms in the acoustic analogy produces little far-field noise. This can be explained, as in Sandham, Salgado & Agarwal (2008), by considering the quadratic nature of the Lilley source terms in (A 11b). A simple expansion of the source term at the fundamental frequency involves terms from both the fundamentalφ 1 and the first harmonicφ 2 .…”

Section: 2mentioning

confidence: 99%

Linear and nonlinear processes in two-dimensional mixing layer dynamics and sound radiation

Cheung

Lele

2009

J. Fluid Mech.

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In this study, we consider the effects of linear and nonlinear instability waves on the near-field dynamics and aeroacoustics of two-dimensional laminar compressible mixing layers. Through a combination of direct computations, linear and nonlinear stability calculations, we demonstrate the significant role of nonlinear mechanisms in accurately describing the behaviour of instability waves. In turn, these processes have a major impact on sound generation mechanisms such as Mach wave radiation and vortex pairing sound. Our simulations show that the mean flow correction, which is required in order to accurately describe the dynamics of large-scale vortical structures, is intrinsically tied to the nonlinear modal interactions and accurate prediction of saturation amplitudes of instability waves. In addition, nonlinear interactions are largely responsible for the excitation and development of higher harmonics in the flow which contribute to the acoustic radiation. Two flow regimes are considered: In supersonic shear layers, where the far-field sound is determined by the instability wave solution at sufficiently high Mach numbers, it is shown that these nonlinear effects directly impact the Mach wave radiation. In subsonic shear layers, correctly capturing the near-field vortical structures and the interactions of the subharmonic and fundamental modes become critical due to the vortex pairing sound generation process. In this regime, a method is proposed to combine the instability wave solution with the Lilley–Goldstein acoustic analogy in order to predict far-field sound.

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“…These instability waves grow downstream and interact non-linearly, thereby generating acoustic waves. There is some evidence, from Sandham et al, 10 that non-linear interaction is a significant source of aerodynamic noise in subsonic jets. In this section, we filter the flow by means of an optimal non-radiating filter, in order to identify the sources of sound in the jet.…”

Section: Iva Problem Descriptionmentioning

confidence: 99%

“…More information can be gained by studying the power spectrum of the pressure field both in the source region and in the far field. The power spectra corresponding to the pressure signal measured at (10, 0) and (10,10) of frequency ω 1 ). Higher harmonics can be seen at frequencies 2ω 1 = 4.4 and 2ω 2 = 6.8, as well as the interaction frequency ω 1 + ω 2 = 5.6.…”

Section: Ivb Flow Analysismentioning

confidence: 99%

See 1 more Smart Citation

On Separating Propagating and Non-Propagating Dynamics in Fluid-Flow Equations

Sinayoko

Agarwal

2009

15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)

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The ability to separate acoustically radiating and non-radiating components in fluid flow is desirable to identify the true sources of aerodynamic sound, which can be expressed in terms of the non-radiating flow dynamics. These non-radiating components are obtained by filtering the flow field. Two linear filtering strategies are investigated: one is based on a differential operator, the other employs convolution operations. Convolution filters are found to be superior at separating radiating and non-radiating components. Their ability to decompose the flow into non-radiating and radiating components is demonstrated on two different flows: one satisfying the linearized Euler and the other the Navier-Stokes equations. In the latter case, the corresponding sound sources are computed. These sources provide good insight into the sound generation process. For source localization, they are found to be superior to the commonly used sound sources computed using the steady part of the flow.

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Jet noise from instability mode interactions

Cited by 8 publications

References 19 publications

Nonlinear interaction model of subsonic jet noise

Nonlinear interaction model of subsonic jet noise

Linear and nonlinear processes in two-dimensional mixing layer dynamics and sound radiation

On Separating Propagating and Non-Propagating Dynamics in Fluid-Flow Equations

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