Wall Shear Stress in Simplified and Scanned Avian Respiratory Airways

Michael Sterling Farnsworth, Brigham Young University


Birds uniquely produce sound through a vocal organ known as a syrinx. The presence of wall shear stress acting on the airway cells of any organism will affect how airway cells develop and multiply. Unique features of avian airway geometry and breathing pattern might have contributed to the development of the syrinx. This thesis examines wall shear stress in the trachea and first bronchi of avian geometries using computational fluid dynamics. The computational fluid dynamic simulations underwent grid- and time-independence studies and were validated using particle image velocimetry. Parameters such as bird size, bronchial branching angle, and breathing waveform were examined to determine conditions that contributed to higher wall shear stress. Both simplified and CT scan-derived respiratory geometries were examined. Maximum wall shear stress for the simplified geometries was found to be highest during the inspiratory phase of breathing and was highest near the pessulus. Maximum wall shear stress in the CT scan-derived geometries was less phase-dependent and was highest near constrictions in the airway. Comparison between scanned and simplified geometry simulations revealed significant differences in wall shear stress magnitudes and flow features. If wall shear stress is found to be important in the development of the syrinx or the advantage of a syrinx, the thesis results are anticipated to aid in characterizing conditions that would have contributed to the development of the syrinx or advantages of syringeal vocal fold position over tracheal vocal fold position.