Glottal Aerodynamics From A Lagrangian Perspective
Open Access
- Author:
- Mcphail, Michael Jesse
- Graduate Program:
- Bioengineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 27, 2016
- Committee Members:
- Michael H Krane, Dissertation Advisor/Co-Advisor
Michael H Krane, Committee Chair/Co-Chair
William O Hancock, Committee Member
Keefe B Manning, Committee Member
Ji Min Lee, Outside Member
Sid Khosla, Special Member - Keywords:
- Phonation
Lagranian Coherent Structures
Aeroacoustics
Voice
Speech - Abstract:
- This dissertation presents a Lagrangian analysis of glottal aerodynamics. Previous research has demonstrated rich glottal jet behavior in normal and disordered phonation. The relevance of these behaviors to glottal aerodynamic resistance and sound generation is not well understood. Improving understanding in these areas provides predictive power for how changes in physiology, through disorder or surgical intervention, affect the effort and quality of voice. The most important contribution of this work is a demonstration that glottal jet inertance is as important as vocal tract inertance. Computational fluid dynamics simulations were conducted with increasing likeness to the physiological problem of phonation. A post-processing analysis identified Lagrangian coherent structures (LCS) from the simulation velocity fields. The LCS enclosed material regions, and the motion of these regions provided the basis of this work. First, canonical aeroacoustic flows were simulated with vortex elements. The LCS identified in these flows were used as control surfaces for aeroacoustic analogies. The motion of material regions were directly related to the sound generated by the flow. Obtaining clear results from more realistic flows proved prohibitively expensive, so the LCS approach yielded no conclusive results concerning phonatory sound production. Flow in a duct through a rigid axisymmetric constriction was analyzed for a range of conditions (Re = 100-1000). The fluid region extruded through the constriction was identified with LCS analysis. The inertial component of the aerodynamic resistance of the constriction was estimated from the extruded fluid region. The inertial component was found to increase for increasing Reynolds number. Results compared well to a slug model, based on idealized motion of the extruded fluid region. Finally, post-processing of fluid-structure interaction simulations of flow through an idealized human upper airway was conducted. Two computational domains were studied, one that enforces symmetry of the glottal jet and one that does not. Both domains were two-dimensional. The fluid extruded through the model vocal folds was identified with LCS. The case with enforced symmetry exhibited a narrow jet extending roughly half the length of the model vocal tract. The case allowing jet asymmetry exhibited a glottal jet that extended roughly half the vocal tract width before breaking down. The contribution to the component of aerodynamic resistance associated with glottal jet inertia was estimated for both types of simulations. The usual linear acoustic inertances of the glottis and vocal tract were also computed. The inertance of the jet was found to be the same order of magnitude as the inertance of the vocal tract during vocal fold opening. As the jet developed, jet inertance grew larger than the typical estimates of glottal and vocal tract inertance. By the time of vocal fold closing, jet inertance was roughly two orders of magnitude greater than vocal tract inertance. These findings strongly suggest that glottal jet inertance is at least commensurate with that of the vocal tract. This has important implications for the fundamental understanding of normal and disordered phonation. Variability in voice may be due to how glottal jet inertance depends on the richness of the glottal jet behavior. Further work should (1) apply a similar approach to three-dimensional simulations of phonation and (2) address the effect of specific disorders, surgical intervention, or supraglottal geometry on glottal jet inertance.