Department of Mechanical Engineering
VIRTUAL GRADUATE SEMINAR IN FLUID MECHANICS
Join on-line via Zoom: https://wse.zoom.us/j/93762992307
Friday, October 2, 2020 | 4:00 p.m. – 5:00 p.m. (EDT)
“Computational Modeling of Ultrasound Generation in the Larynx of Echolocating Bats”
Presented by CHUANXIN NI
(Advisers: Profs. Rajat Mittal & Jung-Hee Seo)
Echolocating bats produce extremely high-frequency sounds from their larynx using a similar phonating organ as other mammals. Significant knowledge gaps, however, still exist in our understanding of the underlying mechanism of ultrasound generation in bat larynx including the precise role of its anatomical structures during the generating process. One hypothesis is that the unique laryngeal membrane and ventricle structures in the bat larynx may play an important role in the high-intensity ultrasound generation. The objective of this study is to develop and employ a high-fidelity computational model to investigate the mechanism of bat ultrasound production. To build up a model of the bat larynx, high-resolution micro-CT scans are obtained to resolve the unique anatomical structures of bat larynx. Using the geometrical parameters obtained from the scans, a 2D canonical model and a lumped-element model are constructed to investigate the frequency response and the resonance characteristics of the bat larynx and vocal tract. Furthermore, by leveraging the results of this linear acoustic analysis, coupled flow-structure-aeroacoustics interaction simulations are planned to perform on a canonical model of the bat larynx with the laryngeal membranes to resolve the nonlinear behavior of ultrasound generation.
“Instantaneous Pressure Field and Aerodynamic Loads Across a Harmonically Pitching Airfoil”
Presented by JIBU TOM JOSE
(Adviser: Prof. Joseph Katz)
Experimental studies of complex unsteady aerodynamic loads on an airfoil undergoing dynamic stall were performed using a harmonically pitching airfoil. The experiments were performed at a Reynolds number of 45,000 in a refractive index matched water tunnel using a NACA 0015 airfoil with 50mm chordlength, oscillating harmonically between 5o and 20o at a reduced frequency of 0.411. Time resolved stereo PIV data were acquired at 1250 frames/s covering the flow on both sides of the foil simultaneously. Assuming a 2D flow, the pressure field around the airfoil was computed by direct integration of material acceleration calculated from the time-resolved velocity field, using an in-house developed, GPU based, parallel-line, omni-directional code. The formation and development of Leading Edge Vortex, and subsequent dynamic stall vortex, and the existence of a phase lag between the incidence angle and the development of suction side structures during upstroke and downstroke were evident from the data. Growth and migration of the pressure minima from the leading to the trailing edge induced pitch up and pitch down moments, respectively.