Application Limits of Conservative Source Interpolation Methods Using a Low Mach Number Hybrid Aeroacoustic Workflow

Schoder, Stefan; Wurzinger, Andreas; Junger, Clemens; Weitz, Michael; Freidhager, Clemens; Roppert, Klaus

doi:10.1142/s2591728520500322

Cited by 24 publications

(14 citation statements)

References 25 publications

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“…Regarding best practice for hybrid aeroacoustics source computations for finite element method [16,17], the right-hand sided of (1) and (2) were computed on the flow lattice and conservatively integrated to the finite element mesh [18,19]. The conservative integration by the cell-centered method was benchmarked by the superior cut-volume cell method with a negligible error of 0.1%.…”

Section: B Step Ii: Source Term Computationmentioning

confidence: 99%

Aeroacoustic wave equation based on Pierce's operator applied to the sound generated by a mixing layer

Schoder

Spieser

Vincent

et al. 2022

28th AIAA/CEAS Aeroacoustics 2022 Conference

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For the first time, this paper presents the sound prediction capabilities of an aeroacoustic wave equation based on Pierce's operator (AWE-PO). The wave equation is applied to a twodimensional mixing layer, providing a solution which is compared with the far-field acoustics of a direct numerical simulation. In contrast to a direct numerical simulation, the computed Lighthill's wave equation and the AWE-PO rely on a hybrid workflow to predict the generated sound. Special attention is put on the visualization and interpretation of the right-hand side of both equations. Finally, the results of the acoustic far-field pressure are compared. It is shown that the radiated sound field's directivity, propagation, and convection effects are captured well for both wave equations. The error of the acoustic intensity compared with the direct numerical simulation is less than 2 dB for Lighthill's equation and AWE-PO. This error is comparable with the errors reported for Lighthill's equation in previous studies. To conclude, the presented wave equation reasonably predicts mixing layer sound, and the acoustic far-field pressure results are in good agreement with the DNS.

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Section: B Step Ii: Source Term Computationmentioning

confidence: 99%

Aeroacoustic wave equation based on Pierce's operator applied to the sound generated by a mixing layer

Schoder

Spieser

Vincent

et al. 2022

28th AIAA/CEAS Aeroacoustics 2022 Conference

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“…The wall boundaries are defined as noslip, no-injection boundary conditions. Secondly, the acoustic source terms are computed on the flow grid and a conservative interpolation to the acoustic grid is performed [41]. Thirdly, the sound propagation is simulated using the finite element method [18].…”

Section: Fluid Dynamics -Cfd -Measurementsmentioning

confidence: 99%

Aeroacoustic Sound Source Characterization of the Human Voice Production-Perturbed Convective Wave Equation

et al. 2021

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The flow-induced sound sources of human voice production are investigated based on a validated voice model. This analysis is performed using a hybrid aeroacoustic workflow based on the perturbed convective wave equation. In the first step, the validated 3D incompressible turbulent flow simulation is computed by the finite volume method using STARCCM+. In a second step, the aeroacoustic sources are evaluated and studied in detail. The formulation of the sound sources is compared to the simplification (neglecting the convective sources) systematically using time-domain and Fourier-space analysis. Additionally, the wave equation is solved with the finite element solver openCFS to obtain the 3D sound field in the acoustic far-field. During the detailed effect analysis, the far-field sound spectra are compared quantitatively, and the flow-induced sound sources are visualized within the larynx. In this contribution, it is shown that the convective part of the sources dominates locally near the vocal folds (VFs) while the local time derivative of the incompressible pressure is distributed in the whole supra-glottal area. Although the maximum amplitude of the time derivative is lower, the integral contribution dominates the sound spectrum. As a by-product of the detailed perturbed convective wave equation source study, we show that the convective source term can be neglected since it only reduces the validation error by 0.6%. Neglecting the convective part reduces the algorithmic complexity of the aeroacoustic source computation of the perturbed convective wave equation and the stored flow data. From the source visualization, we learned how the VF motion transforms into specific characteristics of the aeroacoustic sources. We found that if the VFs are fully closing, the aeroacoustic source terms yield the highest dynamical range. If the VFs are not fully closing, VFs motion does not provide as much source energy to the flow-induced sound sources as in the case of a healthy voice. As a consequence of not fully closing VFs, the cyclic pulsating velocity jet is not cut off entirely and therefore turbulent structures are permanently present inside the supraglottal region. These turbulent structures increase the broadband component of the voice signal, which supports research results of previous studies regarding glottis closure and insufficient voice production.

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“…For applying LH-FE, the hybrid aeroacoustic workflow [39][40][41][42][43] is considered. The workflow can be separated into four different main steps [38]:…”

Section: A Free Propagation Boundary Condition C Fmentioning

confidence: 99%

“…2. The aeroacoustic source terms are interpolated from the flow to a propagation grid while conserving energy [41]. 3.…”

Section: A Free Propagation Boundary Condition C Fmentioning

confidence: 99%

“…In contrast, the propagation grid has to be uniform for adequate wave transportation to prevent numerical reflections in the propagation domain [22]. A common approach is to approximate the wavelength k corresponding with the highest frequency of interest, with 10-20 finite elements [22,[40][41][42][43]48]. For our computations, the frequency range of 1000 Hz to 20 000 Hz is of interest, bringing up…”

Section: Propagation Simulationmentioning

confidence: 99%

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Applicability of two hybrid sound prediction methods for assessing in-duct sound absorbers of turbocharger compressors

et al. 2022

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We analyze the differences between the Ffowcs–Williams and Hawking’s approach and a new sound propagation approach based on the finite element method used for solving Lighthill’s aeroacoustic wave equation for compressible flows. In addition, we discuss the applicability of both methods. The sound propagation approach based on Lighthill’s equation introduces a flow-interface boundary condition, similar to permeable boundaries in the Ffowcs–Williams and Hawking’s analogy, which allows the omission of complex geometries in propagation domains. This enables to reduce numeric effort and storage requirements. Thereby, the hybrid aeroacoustic workflow is considered, for which aeroacoustic source terms are computed to couple a flow and a separated acoustic propagation simulation. We present an extensive investigation of Lighthill’s source terms in the sense of the proposed weak formulation of Lighthill’s equation. For validation, measurements from a cold gas test rig are used. In addition, the possibilities of applying both sound propagation methods for investigating the influence of resonators and sound absorbers are discussed.

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Application Limits of Conservative Source Interpolation Methods Using a Low Mach Number Hybrid Aeroacoustic Workflow

Cited by 24 publications

References 25 publications

Aeroacoustic wave equation based on Pierce's operator applied to the sound generated by a mixing layer

Aeroacoustic wave equation based on Pierce's operator applied to the sound generated by a mixing layer

Aeroacoustic Sound Source Characterization of the Human Voice Production-Perturbed Convective Wave Equation

Applicability of two hybrid sound prediction methods for assessing in-duct sound absorbers of turbocharger compressors

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