Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session AL: Bio-Fluids: Phonation/Glottal Flows |
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Chair: Daniel J. Bodony, University of Illinois at Urbana-Champaign Room: 103A |
Sunday, November 23, 2008 8:00AM - 8:13AM |
AL.00001: Towards Computational Modeling of Phonation Using CT--Based Laryngeal Models S.A. Mohsen Karimian, Rajat Mittal The oscillatory flow generated in human larynx plays a key role in the process of phonation. While much has been done to understand the main features of such flow by using idealized geometry models and simplified flow conditions, there is still little known about the 3D features of laryngeal flow. In this work, anatomically realistic models of the human larynx are used to analyze the fluid dynamics of 3D laryngeal flow using high--fidelity numerical simulations. A Cartesian--grid--based, finite--difference Navier--Stokes solver is used to carry out these simulations. Three--dimensional models of human larynx are extracted from CT images and unstructured surface grids are generated for the model geometries. The pressure driven flow is simulated for a range of Reynolds numbers. The main objective in this work is to understand more in--depth the effect of 3D geometric features of glottal airway on the laryngeal flow structure. [Preview Abstract] |
Sunday, November 23, 2008 8:13AM - 8:26AM |
AL.00002: Aeroacoustic source spectrum for fricative consonant speech sounds Daniel Leonard, Michael Krane The aeroacoustic source spectrum is experimentally determined for flow within an open-ended duct. The source region comprises a jet, formed at a constriction within the duct, which then interacts with an obstacle placed further downstream. The physical model dimensions are commensurate with a life-size vocal tract to enable study of the physics of human speech sound production. Two methods are used to estimate the aeroacoustic source spectrum. The first estimate results from inverse-filtering radiated sound measured outside the duct. The transfer function between the source and microphone locations is constructed from two-microphone-method measurements of the acoustic field inside the duct. The second estimate uses measurements of the jet flow near the obstacle as input to aeroacoustic theory. Comparison of the two estimates is presented. [Preview Abstract] |
Sunday, November 23, 2008 8:26AM - 8:39AM |
AL.00003: Role of jet asymmetry in glottal flow aerodynamics Joel Peltier, Michael Krane, Richard Medvitz Finite element computations of flow through a constriction are used to illuminate the role of the Coanda effect in glottal flow and voice production. Steady-state computations were performed for a series of constriction openings. One set of simulations enforced transverse flow symmetry, while the other allowed the flow to develop naturally. Comparisons of measures relevant to vocal fold vibration and sound production are presented. These comparisons show that the Coanda effect primarily affects the differential transverse force on the vocal fold walls, while the axial force differs little from the symmetric case. These results suggest strongly that the primary role of the Coanda effect in speech is to drive asymmetric vocal fold vibration patterns, and that glottal jet instability contributes to voice perturbations and fluctuations. [Preview Abstract] |
Sunday, November 23, 2008 8:39AM - 8:52AM |
AL.00004: Dynamic importance of unsteady effects in glottal flow aerodynamics Michael Krane, Joel Peltier, Richard Medvitz Finite element computations of flow through a constriction are used to illuminate the role of unsteady flow dynamics in glottal flow and voice production. Unsteady computations were performed for a series of prescribed idealized vocal fold wall motions over reduced frequencies f*=0, 0.04 and 0.08, which correspond to quasi-steady, adult male and adult female speaking voices, respectively. Glottal resistance and estimates of the relative magnitudes of the various terms of the integral momentum equation are presented. Results suggest that glottal flow is inherently unsteady. [Preview Abstract] |
Sunday, November 23, 2008 8:52AM - 9:05AM |
AL.00005: Measurement of glottal flow across scaled up dynamic vocal fold motion Erica Sherman, Michael Krane, Timothy Wei Preliminary measurements of flow of water through a scaled-up model of the human vocal folds will be presented. The vocal fold model is a new design, improving upon that of previous work (Krane, Barry, and Wei, \textit{JASA} 2007). The new model preserves the advantages of the previous experimental rig, enabling time-resolved velocity measurements, but is more physiologically accurate in terms of shape and motion. In particular, both the rocking as well as the oscillatory open/close motions are incorporated into the model. In addition, the vocal fold walls are made of flexible PVC, allowing simulation of fluid-structure interactions along the walls. The details of the new design will be presented, as well as preliminary DPIV measurements of the flow. [Preview Abstract] |
Sunday, November 23, 2008 9:05AM - 9:18AM |
AL.00006: Computational Investigation of Dynamic Glottal Aperture Effects on Respiratory Airflow Jinxiang Xi, Hong Yan, Haibo Dong The periodic movement of the glottal aperture (vocal folds) during tidal breathing has been long recognized as a factor in altering the airflow dynamics in the tracheobrnchial region. The potential influence from these altered flow structures on the transport and deposition of inhaled particles is not known. However, studies devoted to this dynamic physiological feature are scarce due to the complex anatomy in of the larynx and numerical challenges in simulating dynamic geometries. In this study, a high-fidelity immersed boundary solver is used to investigate this problem. A 3D human oral-larynx-lung model is firstly reconstructed from MRI data. The role of the vocal fold movement and associated airflow characteristics such as vortex shedding, Coanda effect etc. during inhalation and exhalation are then numerically studied. [Preview Abstract] |
Sunday, November 23, 2008 9:18AM - 9:31AM |
AL.00007: Quantifying the influence of flow asymmetries on glottal sound sources in speech Byron Erath, Michael Plesniak Human speech is made possible by the air flow interaction with the vocal folds. During phonation, asymmetries in the glottal flow field may arise from flow phenomena (e.g. the Coanda effect) as well as from pathological vocal fold motion (e.g. unilateral paralysis). In this study, the effects of flow asymmetries on glottal sound sources were investigated. Dynamically-programmable 7.5 times life-size vocal fold models with 2 degrees-of-freedom (linear and rotational) were constructed to provide a first-order approximation of vocal fold motion. Important parameters (Reynolds, Strouhal, and Euler numbers) were scaled to physiological values. Normal and abnormal vocal fold motions were synthesized, and the velocity field and instantaneous transglottal pressure drop were measured. Variability in the glottal jet trajectory necessitated sorting of the data according to the resulting flow configuration. The dipole sound source is related to the transglottal pressure drop via acoustic analogies. Variations in the transglottal pressure drop (and subsequently the dipole sound source) arising from flow asymmetries are discussed. [Preview Abstract] |
Sunday, November 23, 2008 9:31AM - 9:44AM |
AL.00008: Unsteady flow motions in the supraglottal region during phonation Haoxiang Luo, Hu Dai The highly unsteady flow motions in the larynx are not only responsible for producing the fundamental frequency tone in phonation, but also have a significant contribution to the broadband noise in the human voice. In this work, the laryngeal flow is modeled either as an incompressible pulsatile jet confined in a two-dimensional channel, or a pressure-driven flow modulated by a pair of viscoelastic vocal folds through the flow--structure interaction. The flow in the supraglottal region is found to be dominated by large-scale vortices whose unsteady motions significantly deflect the glottal jet. In the flow--structure interaction, a hybrid model based on the immersed-boundary method is developed to simulate the flow-induced vocal fold vibration, which involves a three-dimensional vocal fold prototype and a two-dimensional viscous flow. Both the flow behavior and the vibratory characteristics of the vocal folds will be presented. [Preview Abstract] |
Sunday, November 23, 2008 9:44AM - 9:57AM |
AL.00009: Dynamics of Voluntary Cough Maneuvers Shailesh Naire Voluntary cough maneuvers are characterized by transient peak expiratory flows (PEF) exceeding the maximum expiratory flow-volume (MEFV) curve. In some cases, these flows can be well in excess of the MEFV, generally referred to as supramaximal flows. Understanding the flow-structure interaction involved in these maneuvers is the main goal of this work. We present a simple theoretical model for investigating the dynamics of voluntary cough and forced expiratory maneuvers. The core modeling idea is based on a 1-D model of high Reynolds number flow through flexible-walled tubes. The model incorporates key ingredients involved in these maneuvers: the expiratory effort generated by the abdominal and expiratory muscles, the glottis and the flexibility and compliance of the lung airways. Variations in these allow investigation of the expiratory flows generated by a variety of single cough maneuvers. The model successfully reproduces PEF which is shown to depend on the cough generation protocol, the glottis reopening time and the compliance of the airways. The particular highlight is in simulating supramaximal PEF for very compliant tubes. The flow-structure interaction mechanisms behind these are discussed. The wave speed theory of flow limitation is used to characterize the PEF. Existing hypotheses of the origin of PEF, from cough and forced expiration experiments, are also tested using this model. [Preview Abstract] |
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