Theoretical consideration of the flow behavior in oscillating vocal fold

Area of Science:

• Fluid Dynamics
• Acoustic Phonetics
• Bioengineering

Background:

• Self-excited oscillation of vocal folds generates human speech.
• The precise mechanism of vocal fold self-excitation is not fully understood due to unclear airflow characteristics.
• Understanding glottal aerodynamics is crucial for speech production.

Purpose of the Study:

• To theoretically investigate airflow behavior within oscillating constrictions.
• To derive cause-and-effect relationships between glottal width and aerodynamic variables.
• To elucidate the mechanism of self-excited vocal fold oscillation.

Main Methods:

• Analysis of general flow equations for oscillating constrictions.
• Perturbation analysis to derive analytical relationships.
• Examination of unsteady flow effects and Bernoulli effect.

Main Results:

• Unsteady flow effects become significant compared to Bernoulli effect at high phonation frequencies.
• A phase difference emerges between vocal fold motion and glottal pressure, enabling self-excited oscillation.
• Pressure phase-lead increases with the Strouhal number.

Conclusions:

• The interplay of unsteady flow and Bernoulli effects dominates glottal aerodynamics.
• These findings explain vocal fold self-excitation, especially at high frequencies like falsetto.
• Provides insights into glottal aerodynamics for speech science.