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Compressible flow simulations of phonation using realistic vocal tract geometries
KTH, School of Engineering Sciences (SCI), Mechanics, Biomechanics. KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
Aalto University.
KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.ORCID iD: 0000-0001-7330-6965
2019 (English)In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524Article in journal (Refereed) Submitted
Abstract [en]

Voiced speech consists mainly of the source signal that is frequency-weighted by the acoustic filtering of the upper airways and vortex-induced sound through perturbation in the flow field. This study investigates the flow instabilities leading to vortex shedding and the importance of coherent structures in the supraglottal region downstream of the vocal folds for the far-field sound signal. Large eddy simulations of the compressible airflow through the glottal contriction are performed in realistic geometries obtained from three-dimensional magnetic resonance imaging data. Intermittent flow separation through the glottis is shown to introduce unsteady surface pressure through impingement of vortices. Additionally, dominant flow instabilities develop in the shear layer associated with the glottal jet. The aerodynamic perturbations in the near field and the acoustic signal in the far field is examined by means of spatial and temporal Fourier analysis. Furthermore, the acoustic sources due to the unsteady supraglottal flow are identified with the aid of surface spectra and critical regions of amplification of the dominant frequencies of the investigated vowel geometries are identified.

Place, publisher, year, edition, pages
2019.
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-240552OAI: oai:DiVA.org:kth-240552DiVA, id: diva2:1272630
Note

QC 20190119

Available from: 2018-12-19 Created: 2018-12-19 Last updated: 2019-01-29Bibliographically approved
In thesis
1. Modelling the Production and Propagation of Sound in Individual Human Vocal Tracts
Open this publication in new window or tab >>Modelling the Production and Propagation of Sound in Individual Human Vocal Tracts
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Voice generation and the expression through speech are of vital importance for communication. The human upper airways are the origin of the process of speech production, which involves a modulation of the periodically pulsed pressure from the lungs by the vocal tract volume. In this work, phonation and voiced speech are investigated through both low- and high-order models, which are applied to vocal tract geometries of increasing complexity. Initially, the effect of variations of vocal fold closure, fundamental frequency, and vocal tract length on the computed acoustic signal is examined through parameter studies based on one-dimensional wave reflection analogues. Eventually, unsteady large eddy simulations based on the compressible Navier-Stokes equations are carried out to compute the pressure fluctuations and the associated distribution of resonance modes as a result of the interaction with the static vocal tract. Thus it is possible to calculate tonalities from the entire audible range of frequencies from 20 to 20000 Hz. In particular the inharmonic broadband sound component produced predominantly by coherent structures in the upper airways and at frequencies above 2 kHz is resolved in the current study, which is not captured by low-order models based on wave equations. Furthermore, three-dimensional numerical meshes based on surface representations of the human upper airways under voiced speech from magnetic resonance imaging (MRI) data of a healthy male subject are applied. These are necessary to resolve high-order acoustic modes that would not be represented by simplified geometries. Validation and verification of the chosen methods are achieved through comparison with experimentally obtained speech data, as well as Helmholtz eigenfrequencies of the considered vowel pronunciations. The main scope of this work is the assessment of acoustic sources and the conditions for aerodynamic sound being produced and propagated in the upper airways during phonation. The distribution of acoustic sources involved in the generation of the dominant frequencies are identified by application of acoustic analogies as well as surface Fourier transformation of the acoustic pressure fluctuations. However, the human upper airways do not only embrace the source of phonation and affect the modulation of the voice. Moreover, unwanted sounds may be generated in the upper airways due to elastic, collapsible parts that are susceptible to flow-induced vibration and resonance. The sound resulting from fluid-structure interaction in the upper respiratory tract, commonly known as snoring, can be an important indicator for underlying breathing disorders, such as obstructive sleep apnea (OSA). In a smaller part of this project, the flow structures and acoustic sources as a result of the interaction of shear flow of various Reynolds numbers with an elastic element are computed. The geometric dimensions are chosen to be representative of average physical values of the upper respiratory tract. Onset of tissue vibrations and resonance effects are investigated for a range of parameters of both solid and fluid. The obtained results of this work are aimed to contribute also to the development of a computational tool that assists physicians in the assessment of the airway function and the effectiveness of treatment plans prior to their application.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019
Series
TRITA-MEK, ISSN 0348-467X ; 2019:02
Keywords
Biomechanics, Vocal Tract Acoustics, Numerical Flow Simulation, Fluid-Structure Interaction
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-240556 (URN)978-91-7873-064-3 (ISBN)
Public defence
2019-01-31, F3, Lindstedtsvägen 26, Plan 2, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20181220

Available from: 2018-12-21 Created: 2018-12-19 Last updated: 2018-12-21Bibliographically approved

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Mihaescu, Mihai

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