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TECHNICAL PAPERS: Fluids/Heat/Transport

Flow Visualization and Acoustic Consequences of the Air Moving Through a Static Model of the Human Larynx

[+] Author and Article Information
Bogdan R. Kucinschi, Ronald C. Scherer

Department of Otolaryngology, Head and Neck Surgery,  University of Cincinnati Medical Center, Cincinnati, OH 45267-0528

Kenneth J. DeWitt, Terry T. Ng

Mechanical, Industrial, and Manufacturing Engineering Department,  University of Toledo, 2801 West Bancroft, Toledo, OH 43606

J Biomech Eng 128(3), 380-390 (Nov 17, 2005) (11 pages) doi:10.1115/1.2187042 History: Received July 12, 2005; Revised November 17, 2005

Flow visualization with smoke particles illuminated by a laser sheet was used to obtain a qualitative description of the air flow structures through a dynamically similar 7.5× symmetric static scale model of the human larynx (divergence angle of 10deg, minimal diameter of 0.04cm real life). The acoustic level downstream of the vocal folds was measured by using a condenser microphone. False vocal folds (FVFs) were included. In general, the glottal flow was laminar and bistable. The glottal jet curvature increased with flow rate and decreased with the presence of the FVFs. The glottal exit flow for the lowest flow rate showed a curved jet which remained laminar for all geometries. For the higher flow rates, the jet flow patterns exiting the glottis showed a laminar jet core, transitioning to vortical structures, and leading spatially to turbulent dissipation. This structure was shortened and tightened with an increase in flow rate. The narrow FVF gap lengthened the flow structure and reduced jet curvature via acceleration of the flow. These results suggest that laryngeal flow resistance and the complex jet flow structure exiting the glottis are highly affected by flow rate and the presence of the false vocal folds. Acoustic consequences are discussed in terms of the quadrupole- and dipole-type sound sources due to ordered flow structures.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 2

Geometry of vocal folds and false vocal folds. The real life dimensions are indicated (the dimensions in the model are 7.5 times larger).

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Figure 3

Flow visualization for the symmetric glottis (no false vocal folds)

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Figure 4

Flow visualization for the symmetric glottis, narrow false vocal fold gap (0.102cm real life)

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Figure 5

Flow visualization for the symmetric glottis, downstream of the false vocal fold gap. The two sides are the diverging surfaces of the false vocal folds.

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Figure 6

Flow visualization for the symmetric glottis, wide false vocal fold gap (0.675cm real life)

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Figure 7

Illustration of the vortex shedding (no false vocal folds, 144.4cm3∕s)

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Figure 8

The Strouhal number of vortex shedding vs Reynolds number. The values 0.604 and 0.267cm correspond to the axial distance between the upper surface of the true vocal folds and the lower surface of the false vocal folds.

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Figure 9

Ratio of vortex convection velocity to jet centerline velocity vs Reynolds number

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Figure 10

Flow pattern at a relatively high flow rate (533cm3∕s, narrow false vocal fold gap at 0.267cm (2cm, model) downstream of the vocal folds, obtained with the high-speed camera at 10,000frames∕s (exposure time 90μs)

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Figure 11

Sound spectra for high flow rates (444–667cm3∕s), narrow false vocal fold gap at 0.267cm (2cm, model) downstream of the vocal folds

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Figure 12

Frequency of the highest spectral peak vs the real life flow rate, with no false folds and narrow false folds gap

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Figure 1

Experimental apparatus

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