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Hemi-laryngeal Setup for Studying Vocal Fold Vibration in Three Dimensions
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Examining the Quasi-Steady Airflow Assumption in Irregular Vocal Fold Vibration
Xiaojian Wang1, Xudong Zheng1,2, Ingo R Titze3
1Department of Mechanical Engineering, University of Maine, Orono, ME 04473, USA.
Applied Sciences (Basel, Switzerland)
|March 23, 2026
Summary
The quasi-steady flow assumption (QSFA) has limitations in phonation biomechanics, especially at higher frequencies. Unsteady flow and vocal tract inertance significantly impact accuracy, challenging its widespread use.
Area of Science:
- Biomechanics of phonation
- Fluid dynamics
- Acoustics
Background:
- The quasi-steady flow assumption (QSFA) simplifies phonation modeling by treating glottal flow as steady.
- QSFA ignores vocal fold dynamics and unsteady flow phenomena, potentially limiting its accuracy.
Purpose of the Study:
- To investigate the limitations of QSFA in human phonation.
- To evaluate the impact of phonation frequency, vocal tract air inertance, and glottal shape on QSFA validity.
Main Methods:
- Numerical simulations comparing dynamic, pseudo-static, and quasi-steady flow models.
- Analysis of glottal flow rate, wall pressure, and sound spectrum under varying conditions.
- Inclusion of two sets of irregular glottal shapes.
Main Results:
- QSFA errors in flow rate and pressure increase significantly with frequency (e.g., 100 Hz vs. 500 Hz) due to flow unsteadiness.
- Vocal tract air inertance exacerbates prediction errors when interacting with unsteady glottal flow.
- Flow unsteadiness affects the perceptually important harmonic energy ratio.
Conclusions:
- QSFA validity is compromised at higher phonation frequencies due to flow unsteadiness.
- Vocal fold motion and irregular glottal shapes have minor effects on QSFA validity compared to frequency and air inertance.
- The study highlights the need to consider flow unsteadiness for accurate phonation modeling.
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