Scattering of entropy waves into sound by isolated aerofoils

Guzmán-Iñigo, Juan; Durán, I.; Morgans, Aimee S.

doi:10.1017/jfm.2021.569

Cited by 5 publications

(4 citation statements)

References 86 publications

(131 reference statements)

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“…10). This unsteady load generates an acoustic field by virtue of the third law of Newton as shown in [34] and [35] that interacts and modulates the sound created by entropy acceleration.…”

Section: Stator Rowmentioning

confidence: 99%

Effect of clocking on entropy noise generation within an aeronautical high pressure turbine stage

Pinelli

Marconcini

Pacciani

et al. 2022

Journal of Sound and Vibration

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“…10). This unsteady load generates an acoustic field by virtue of the third law of Newton as shown in [34] and [35] that interacts and modulates the sound created by entropy acceleration.…”

Section: Stator Rowmentioning

confidence: 99%

Effect of clocking on entropy noise generation within an aeronautical high pressure turbine stage

Pinelli

Marconcini

Pacciani

et al. 2022

Journal of Sound and Vibration

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“…In, 21,22 it was found that non-plane wave effects were important at medium frequencies and some modelling of their effects was achieved. Other recent efforts to relax the quasi-onedimensional assumptions have been based on Rapid Distortion Theory, 23 with models developed for the sound generated by entropy interacting with isolated blades 24,25 and cascades. 26 An alternative way to model the sound generation due to non-plane entropy waves is to use the acoustic analogy theory pioneered by Lighthill.…”

Section: Introductionmentioning

confidence: 99%

Sound generated by axisymmetric non-plane entropy waves passing through flow contractions

Yang

Guzmán-Iñigo

Morgans

2022

International Journal of Aeroacoustics

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For a single-component perfect gas, entropy perturbations are associated with the difference between the overall density fluctuation and that coming from the acoustic perturbation. Entropy perturbations can generate sound when accelerated/decelerated by a non-uniform flow and this is highly relevant to thermoacoustic instabilities for gas turbines and rocket engines, and to noise emission for aero-engines. Widely used theories to model this entropy-generated sound rely on quasi-1D assumptions for which questions of validity were raised recently from both numerical and experimental studies. In the present work, we build upon an acoustic analogy theory for this problem. This theory was initiated by Morfey (J. Sound Vib. 1973) and Ffowcs Williams and Howe (J. Fluid Mech. 1975) about 50 years ago and extended recently by Yang, Guzmán-Iñigo and Morgans (J. Fluid Mech. 2020) to study the effect of non-plane entropy waves at the inlet of a flow contraction on its sound generation. Comparisons against both numerical simulations and previous theory are performed to validate the results.

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“…For instance, acoustic waves can be scattered into vortical waves by sharp edges [3] or dissipated into heat (entropy) by viscous effects. Likewise, entropy waves can generate sound when accelerated/decelerated (mean-flow gradients) [4,5] or when interacting with solid boundaries, such as aerofoils [6][7][8]. This is termed entropy noise and is particularly relevant in the context of confined combustion, as occurs in the combustors of gas turbines [9] and rockets engines [10].…”

Section: Introductionmentioning

confidence: 99%

On the scattering of entropy waves at sudden area expansions

Guzmán-Iñigo,

Yang,

Gaudron

et al. 2021

Preprint

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In this work, we investigate both numerically and theoretically the sound generated by entropy waves passing through sudden area expansions. This is a canonical configuration representing internal flows with flow separation and stagnation pressure losses. The numerical approach is based on a triple decomposition of the flow variables into a steady mean, a small-amplitude coherent part, and a stochastic turbulent part. The coherent part contains acoustic, vortical, and entropy waves. The mean flow is obtained as the solution of the Reynolds-Averaged Navier-Stokes (RANS) equations. The equations governing the coherent perturbations are linearised and solved in the frequency domain. To account for the effect of turbulence on the coherent perturbations, a frozen eddy viscosity model is employed. When entropy fluctuations pass through the area expansion, the generated entropy noise behaves as a low-pass filter. The numerical predictions of the noise at low frequencies are compared to the predictions of compact, quasi-one-dimensional, and isentropic theory and large discrepancies are observed. An alternative model for the generated entropy noise tailored for area expansions is then proposed. Such model is based on the conservation of mass, momentum, and energy written in integral form. The model assumes zero frequency and the one-dimensionality of the flow variables far upstream and downstream of the expansion. The predictions of this model agree well with the numerical simulations across a range of finite subsonic Mach numbers including low, intermediate, and high Mach numbers. The contributions of this work are both numerical and theoretical. Numerically, a triple decomposition adapted to high-Mach-number, compressible flows is introduced for the first time in the context of acoustic simulations. From a theoretical point of view, the model proposed here represents the first quasi-steady model that captures correctly the low-frequency entropy noise generated at sudden area expansions, including at high subsonic Mach numbers.

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Scattering of entropy waves into sound by isolated aerofoils

Abstract: Abstract

Cited by 5 publications

References 86 publications

Effect of clocking on entropy noise generation within an aeronautical high pressure turbine stage

Effect of clocking on entropy noise generation within an aeronautical high pressure turbine stage

Sound generated by axisymmetric non-plane entropy waves passing through flow contractions

On the scattering of entropy waves at sudden area expansions

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