On the scattering of entropy waves at sudden area expansions

Guzmán-Iñigo, Juan; Yang, Dong; Gaudron, Renaud; Morgans, Aimee S.

doi:10.1016/j.jsv.2022.117261

Cited by 6 publications

(7 citation statements)

References 63 publications

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“…A slip boundary condition is applied on the lateral wall of the upstream duct, along with a zero-gradient condition for the temperature and pressure. This ensures that the mean flow variables remain uniform in the upstream duct, which greatly simplifies the post-processing procedure with negligible impact on numerical results at low frequencies, as demonstrated in a separate work [32]. Finally, a no-slip boundary condition along with a zero-gradient condition for the temperature and pressure is prescribed on all remaining boundaries.…”

Section: A Mean Flow Simulationsmentioning

confidence: 99%

“…In that case, the acoustic response of the sudden area expansion is fully characterised by the Scattering Matrix (or S-matrix) S, corresponding to the first two rows and columns of A. The impact of incoming entropy waves on the response of sudden area expansions has been investigated in separate works [31,32].…”

Section: B Fluctuating Variablesmentioning

confidence: 99%

“…The incoming Riemann invariants at the inlet and outlet can be set to any complex value. More information about these solvers and their validation can be found in [32].…”

Section: B Linearised Flow Simulationsmentioning

confidence: 99%

“…In theory, both approaches can be used to characterise the acoustic response of sudden area expansions containing a (subsonic) compressible mean flow. In practice, several numerical difficulties arise at intermediate and high Mach numbers [28,32], and the existing numerical studies focus on low Mach number flows only [26][27][28]30]. It was established in these numerical studies that the acoustic response of sudden area expansions is almost frequency-independent at low Helmholtz numbers [26][27][28].…”

Section: Introductionmentioning

confidence: 99%

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Variation of Acoustic Energy Across Sudden Area Expansions Sustaining a Subsonic Flow

2023

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The acoustic energy balance of a sudden area expansion is known to be altered in the presence of a mean flow. In this work, Ronneberger’s quasi-steady model describing the acoustic response of a sudden area expansion sustaining a subsonic mean flow of arbitrary Mach number is revisited using the acoustic absorption coefficient, shown to be a function of the inlet Mach number [Formula: see text], cross-sectional area ratio [Formula: see text], and upstream acoustic reflection coefficient [Formula: see text]. These analytical predictions are tested using a two-step numerical strategy, whereby the mean flow variables are obtained using Reynolds-averaged Navier–Stokes simulations and the fluctuating variables are computed using in-house linearized Navier–Stokes equations solvers. The agreement between the analytical model and the numerical results is found to be excellent for all geometries, mean flows, and acoustic boundary conditions investigated. The generation of acoustic energy by the flow expansion is observed analytically and numerically for high-Mach-number flows undergoing a slight sudden area increase for given acoustic boundary conditions. Conversely, it is found that substantial acoustic energy damping occurs across sudden area expansions characterized by a wide range of parameters [Formula: see text]. Moreover, entropy and vorticity fluctuations are found to be generated at the sudden area expansion, but entropy fluctuations are shown to have a negligible impact on the acoustic response of the area expansion at low and intermediate Mach numbers. Finally, the analytical model is found to be reasonably accurate up to Helmholtz numbers [Formula: see text], corresponding to the frequency range of many industrial applications.

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Section: A Mean Flow Simulationsmentioning

confidence: 99%

Section: B Fluctuating Variablesmentioning

confidence: 99%

“…The incoming Riemann invariants at the inlet and outlet can be set to any complex value. More information about these solvers and their validation can be found in [32].…”

Section: B Linearised Flow Simulationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Variation of Acoustic Energy Across Sudden Area Expansions Sustaining a Subsonic Flow

2023

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“…39,40 A slip boundary condition is again imposed on the walls. Fully non-reflective acoustic boundary conditions are imposed at both the inlet and the outlet, 41 so that only reflected and transmitted plane acoustic waves exist, respectively, at the far up- and downstream ducts. An entropy perturbation, s˜0, is inserted at the inlet as a boundary condition.…”

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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