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

3aSC5 Experimental observations on the influence of supraglottal flow structures on phonation Zhaoyan Zhang and Juergen Neubauer School of Medicine, University of California Los Angeles, CA, USA October 28, 2009 158 th ASA Meeting, San Antonio, Texas Acknowledgment: Research supported by NIH R01-DC009229

Supraglottal Flow Field • Once separated from the vocal folds, the flow is susceptible to Vortex roll-up many flow instabilities. And turbulence • Highly three-dimensional and complex: recirculation – Jet attachment to one vocal fold wall (asymmetric jet or the Coanda effect) Jet flow – Recirculation – Jet instabilities (vortex shedding and roll-up) Flow – Jet reattachment separation – Turbulence flow

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 on 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 Pressure Transducer Microphones Outside Microphone Flow supply Expansion Chamber Flow meter Vocal Trachea Tract (2.8 cm) (11 cm) Self-oscillating Vocal fold model

Two-layer self-oscillating rubber vocal fold model Vocal folds Side View Top 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

Without cylinder with vocal tract -10 (2.54 × 2.54 cm -8 -6 and 2.5 cm long) -4 Flow -2 0 2 4 Vocal folds 6 8 10 -10 -5 0 5 10 Cylinder on the left Cylinder at the center Cylinder on the right -10 -10 -10 -8 -8 -8 -6 -6 -6 -4 -4 -4 -2 -2 -2 0 0 0 2 2 2 4 4 4 6 6 6 8 8 8 10 10 10 -10 -5 0 5 10 -10 -5 0 5 10 -10 -5 0 5 10

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

Effect on Phonation: Acoustic pressure amplitude 1.15 Outside acoustic Subglottal Acoustic Pressure pressure Outside Acoustic Pressure 1.1 low-pass filtered with Mean Subglottal Pressure Normalized amplitude a cut-off of 2.5 kHz 1.05 1 0.95 Except for three regions, the change 0.9 is within 5% 0.85 0.8 0.75 -5 -4 -3 -2 -1 0 1 2 3 4 5 Left-Right Location (mm) Cylinder location in the left-Right direction (mm)

Effect on Phonation frequency F 0 Subglottal acoustic pressure • Phonation frequency F 0 0 1000 stayed at 144 Hz for -1 900 most locations as the -2 800 -3 cylinder was traversed in 700 -4 the left-right direction. 600 -5 • In regions of significant 500 -6 amplitude change, F0 400 -7 changed between 142 -8 300 and 148 Hz. -9 200 -10 • No significant changes 100 -11 in spectral shape 0 10 20 30 40 50 Cylinder location in the left-Right direction

Cylinder traversed in the flow direction 5 2 1.15 Subglottal Acoustic Pressure Outside Acoustic Pressure 1.1 Mean Subglottal Pressure 1.05 1 0.95 0.9 0.85 0.8 0.75 -5 -4 -3 -2 -1 0 1 2 3 4 5 Left-Right Location (mm) 1 3 4

Location 1: on the left -- Acoustic pressure amplitude 1.1 Normalized amplitude 1 0.9 0.8 0.7 Maximum amplitude change is 55% 0.6 Subglottal Acoustic Pressure Influence range: 0.5 Outside Acoustic Pressure Mean Subglottal Pressure <2.5 mm 0.4 0 1 2 3 4 5 6 7 Axial Distance (mm) Cylinder location in the flow direction (mm) Influence range

Location 2: slightly left -- Acoustic pressure amplitude 1.25 Subglottal Acoustic Pressure Normalized amplitude 1.2 Outside Acoustic Pressure Mean Subglottal Pressure 1.15 1.1 Maximum amplitude 1.05 change is 20% 1 0.95 0 1 2 3 4 5 6 7 Axial Distance (mm) Cylinder location in the flow direction (mm)

Location 3: glottal center -- Acoustic pressure amplitude 1.4 1.2 Normalized amplitude 1 0.8 0.6 Subglottal Acoustic Pressure Outside Acoustic Pressure Maximum amplitude Mean Subglottal Pressure 0.4 change is 80% 0.2 Influence range: <1 mm 0 -2 0 2 4 6 8 Axial Distance (mm) Cylinder location in the flow direction (mm) Influence range

Location 4: slight right -- Acoustic pressure amplitude 1.05 1 Normalized amplitude 0.95 0.9 0.85 0.8 Maximum amplitude 0.75 change is 35% Subglottal Acoustic Pressure 0.7 Outside Acoustic Pressure Influence range: Mean Subglottal Pressure 0.65 <2.2 mm 0 1 2 3 4 5 6 7 Axial Distance (mm) Cylinder location in the flow direction (mm) Influence range

Location 5: on the right -- Acoustic pressure amplitude 1.1 Subglottal Acoustic Pressure Outside Acoustic Pressure 1.08 Normalized amplitude Mean Subglottal Pressure 1.06 1.04 Maximum amplitude 1.02 change is 9% Influence range: 1 <0.5 mm 0.98 0 1 2 3 4 5 6 7 Axial Distance (mm) Cylinder location in the flow direction (mm) Influence range

Regions of significance 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 Region 2 Region 1 supraglottal flow.

Without cylinder -10 -8 -6 -4 Flow -2 0 2 4 Vocal folds 6 8 10 -10 -5 0 5 10 Cylinder on the left Cylinder at the center Cylinder on the right -10 -10 -10 -8 -8 -8 -6 -6 -6 -4 -4 -4 -2 -2 -2 0 0 0 2 2 2 4 4 4 6 6 6 8 8 8 10 10 10 -10 -5 0 5 10 -10 -5 0 5 10 -10 -5 0 5 10

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