Acoustic-entropy coupling behavior and acoustic scattering properties of a Laval nozzle

Ullrich, Wolfram C.; Gikadi, Jannis; Jörg, Christoph; Sattelmayer, Thomas

doi:10.2514/6.2014-3193

Cited by 5 publications

(2 citation statements)

References 23 publications

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“…Furthermore, the effects of turbulent mixing or flow separation on indirect combustion noise as described by Howe 19 can also be studied further within this specific numerical context. All of these effects have not been studied in previous EWG works, which are based on the coupling of RANS simulations with computational aeroacoustic (CAA) methodologies, 20,21 unsteady RANS simulations, 12,13 Euler simulations, and even analytical modeling. 9,11,22 To reach the need for higher-fidelity flow predictions, Large Eddy Simulation (LES) seems to be a first good candidate to simulate the high Reynolds number EWG subsonic test case, and provide further insight into the physical phenomena of indirect combustion noise generation and transmission.…”

Section: Introductionmentioning

confidence: 99%

Large-Eddy-simulation prediction of indirect combustion noise in the entropy wave generator experiment

Moreau

Becerril

Gicquel

2017

International Journal of Spray and Combustion Dynamics

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Compact and non-compact analytical solutions of the subsonic operating point of the entropy wave generator experiment are compared with detailed numerical results obtained by large Eddy simulations. Two energy deposition methods are presented to account for the experimental ignition sequence and geometry: a single-block deposition as previously used and a delayed deposition that reproduces the experimental protocle closely. The unknown inlet acoustic reflection coefficient is assumed to be fully reflective to be more physically consistent with the actual experimental setup. The time delay between the activation of the heating modules must be considered to retrieve the temperature signal measured at the vibrometer and pressure signals at the microphones. Moreover, pressure signals extracted from the large Eddy simulations in the outlet duct using the delayed ignition model clearly reproduce the experimental signals better than the analytical models. An additional simulation with actual temperature fluctuations directly injected at the inlet of the computational domain clearly shows that the pressure fluctuations produced by the acceleration of the hot slug yields indirect noise almost entirely. Finally, the entropy spot is shown to be distorted when convecting through the turbulent flow in the entropy wave generator nozzle. Its amplitude decreases and its shape is dispersed, but hardly any dissipation occurs. The distortion appears to be negligible through the nozzle and become important only when convected over a long distance in the downstream duct. As the dominant frequencies of the entropy wave generator entropy forcing are very low, the effects of dispersion by the mean flow are however weak.

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Section: Introductionmentioning

confidence: 99%

Large-Eddy-simulation prediction of indirect combustion noise in the entropy wave generator experiment

Moreau

Becerril

Gicquel

2017

International Journal of Spray and Combustion Dynamics

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“…Additionally, some authors have considered the energy equation for laminar flows, e.g. Schulze et al [52] to characterise perforations and Ullrich et al [53] to investigate the acoustic-entropic coupling in a Laval nozzle. In this work, we consider both the effect of turbulence and the energy equation in the governing equations.…”

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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