Experimental observations on the influence of supraglottal flow - - PowerPoint PPT Presentation

Experimental observations on the influence of supraglottal flow structures

• n phonation

Zhaoyan Zhang and Juergen Neubauer

School of Medicine, University of California Los Angeles, CA, USA October 28, 2009 158th ASA Meeting, San Antonio, Texas Acknowledgment: Research supported by NIH R01-DC009229

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Supraglottal Flow Field

Jet flow Vortex roll-up And turbulence Flow separation flow

• Once separated from the vocal

folds, the flow is susceptible to many flow instabilities.

• Highly three-dimensional and

complex:

– Jet attachment to one vocal fold wall (asymmetric jet or the Coanda effect) – Recirculation – Jet instabilities (vortex shedding and roll-up) – Jet reattachment – Turbulence

recirculation

Motivation

• What roles do they play in phonation?
• Practical concern

– It is computationally expensive to accurately resolve these complex flow features – How large an error if some or all of these phenomena are neglected in models? – Identify the appropriate degree of complexity for the glottal flow model

Studies on the Supraglottal Flow

• Experiments:

– Teager and Teager, 1985 – Pelorson et al., 1994 – Shinwari et al., 2003 – Zhang et al., 2004 – Triep et al., 2005 – Erath and Plesniak 2006 – Neubauer et al., 2007 – Drechsel and Thomson, 2008

• Numerical simulations:

– Zhao et al., 2002 – Hofmans et al., 2003 – Suh and Frankel, 2007 – Tao et al., 2007 – Sciamarella and Le Quere, 2008 – Luo et al. (2009)

Previous Studies

• Most of these studies focused on describing the

supraglottal flow field, instead of on its relevance to phonation

• Pelorson et al., 1994; Hofmans et al., 2003

– Numerical & experimental studies with a static vocal fold model – Coanda effect (jet attachment to one glottal wall) and transition to turbulence may not occur in phonation, therefore not relevant.

• Sciamarella and Le Quere, 2008

– Numerical study; imposed vocal fold motion – Unsteadiness (jet instabilities, vortex roll-up) of the fully developed flow past the constriction does not significantly affect the velocity or pressure profiles within the constriction.

• The influence on phonation in a self-oscillating model is

essentially unexplored

Objective

• Quantify the effects of supraglottal flow structures
• n phonation
• Approach:

– Use self-oscillating models – Disturb the supraglottal flow field

• Disturb the flow by traversing a cylinder in the left-right and

flow direction

• Variables of interest

– Sound amplitude and spectral shape – Phonation frequency – Vibration pattern

Experimental Setup

Expansion Chamber Microphones Pressure Transducer Flow supply

Self-oscillating Vocal fold model

Flow meter Outside Microphone

Trachea (11 cm) Vocal Tract (2.8 cm)

Two-layer self-oscillating rubber vocal fold model

Vocal folds

Top View Side View

Disturbing the supraglottal flow

• A cylinder aligned in the anterior-posterior

direction was traversed in both the left-right and flow directions.

– The cylinder is long enough to cover the entire anterior-posterior span of the vocal fold model

Vocal fold model cylinder

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Vocal folds Flow Without cylinder

Cylinder on the left Cylinder at the center Cylinder on the right

with vocal tract (2.54×2.54 cm and 2.5 cm long)

Observation on the disturbed supraglottal flow

• Jet flow was either deflected to one side or split into two

jets

• Implications (as the cylinder moved close to the glottal

exit):

– Jet flow may be forced to attach to one vocal fold, leading to asymmetric flow separation within the glottis – Asymmetric recirculation between the sides of the jet flow, leading to different pressures on the superior surfaces of the two folds. – Pressure recovery associated with jet diffusion/expansion may be significantly altered. – Vortex patterns and evolution significantly altered.

Cylinder traversed in the left-right direction

Cylinder axial location at x= 1.5 mm Max(D)= 3 mm

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1 2 3 4 5 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 Left-Right Location (mm) Subglottal Acoustic Pressure Outside Acoustic Pressure Mean Subglottal Pressure

Effect on Phonation: Acoustic pressure amplitude

Outside acoustic pressure low-pass filtered with a cut-off of 2.5 kHz

Normalized amplitude Cylinder location in the left-Right direction (mm)

Except for three regions, the change is within 5%

Effect on Phonation frequency F0

• Phonation frequency F0

stayed at 144 Hz for most locations as the cylinder was traversed in the left-right direction.

• In regions of significant

amplitude change, F0 changed between 142 and 148 Hz.

• No significant changes

in spectral shape

Subglottal acoustic pressure 10 20 30 40 50 100 200 300 400 500 600 700 800 900 1000

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Cylinder location in the left-Right direction

Cylinder traversed in the flow direction

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1 2 3 4 5 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 Left-Right Location (mm) Subglottal Acoustic Pressure Outside Acoustic Pressure Mean Subglottal Pressure

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Location 1: on the left

• - Acoustic pressure amplitude

Normalized amplitude

1 2 3 4 5 6 7 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 Axial Distance (mm) Subglottal Acoustic Pressure Outside Acoustic Pressure Mean Subglottal Pressure

Maximum amplitude change is 55% Influence range: <2.5 mm

Influence range

Cylinder location in the flow direction (mm)

Location 2: slightly left

• - Acoustic pressure amplitude

Normalized amplitude

1 2 3 4 5 6 7 0.95 1 1.05 1.1 1.15 1.2 1.25 Axial Distance (mm) Subglottal Acoustic Pressure Outside Acoustic Pressure Mean Subglottal Pressure

Maximum amplitude change is 20%

Cylinder location in the flow direction (mm)

Location 3: glottal center

• - Acoustic pressure amplitude

Normalized amplitude

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2 4 6 8 0.2 0.4 0.6 0.8 1 1.2 1.4 Axial Distance (mm) Subglottal Acoustic Pressure Outside Acoustic Pressure Mean Subglottal Pressure

Maximum amplitude change is 80% Influence range: <1 mm Influence range

Cylinder location in the flow direction (mm)

Location 4: slight right

• - Acoustic pressure amplitude

Normalized amplitude

1 2 3 4 5 6 7 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 Axial Distance (mm) Subglottal Acoustic Pressure Outside Acoustic Pressure Mean Subglottal Pressure

Maximum amplitude change is 35% Influence range: <2.2 mm

Influence range

Cylinder location in the flow direction (mm)

Location 5: on the right

• - Acoustic pressure amplitude

Normalized amplitude

1 2 3 4 5 6 7 0.98 1 1.02 1.04 1.06 1.08 1.1 Axial Distance (mm) Subglottal Acoustic Pressure Outside Acoustic Pressure Mean Subglottal Pressure

Maximum amplitude change is 9% Influence range: <0.5 mm

Influence range

Cylinder location in the flow direction (mm)

• Region 1: Inside or immediately

downstream (< 2mm) of the glottal exit

• Increased back pressure, and

therefore decreased transglottal pressure, due to flow blockage by the cylinder

• Region 2: roughly corresponds to

the shear layers of the jet

• Presence of cylinder caused the jet

to change direction

• Changed the flow separation

pattern within the glottis

• Otherwise, phonation is not

sensitive to changes in the supraglottal flow.

Regions of significance

Region 1 Region 2

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Vocal folds Flow Without cylinder

Cylinder on the left Cylinder at the center Cylinder on the right

Summary

• Large influence on phonation was observed when

the supraglottal flow was disturbed either in the shear layers or a region within 2 mm above the model.

– Changed back pressure due to flow blockage by the cylinder – Changed the flow separation pattern within the glottis

• Otherwise, phonation was not sensitive to changes

in the supraglottal flow field,

– Jet instabilities, recirculation, and transition to turbulence have negligible influence on the low- frequency component of phonation (onset, F0, sound amplitude)

Further Question

• Is there any mechanism in human phonation

that can cause significant changes in jet axis, without using a cylinder?

– Jet instabilities and turbulence have limited influence on jet axis. – False vocal folds? – Asymmetries in the vocal folds may significantly affect jet axis movement