Session: Government Agency Student Posters

Paper Number: 173136

Experiment to Identify the Physics of Human Whistling 

Human whistling is one of the lesser-understood natural phenomena that involves a subtle yet strong interplay between fluid mechanics and acoustics. A whistle is typically produced by raising the tongue against the roof of the mouth to form an intraoral constriction (first orifice), while simultaneously shaping the lips into a pursed, elliptical like opening (second orifice). The air expelled from the lungs passes through these two orifices, with the mouth cavity acting as a resonant chamber in between. A stable and tonal whistle is generally observed only within a narrow range of flow rates and geometric configurations, forming a critical “sweet spot.” This coordination of tongue position, lip shape, and airflow is something many people struggle to achieve, and the underlying fluid dynamic mechanisms governing this selectivity remain poorly understood.

In this work, we develop an experimental model inspired by human whistling, consisting of an axisymmetric resonant chamber bounded by two smooth-edged orifices. The chamber is supplied with air at a controlled flow rate using a calibrated flow meter, and the flow is seeded with smoke for visualization of jet structures. Both of the orifices are fabricated using a high-resolution resin 3D printer to replicate the smooth contours of human lips and oral surfaces. We employ a hot-wire anemometer to measure velocity fluctuations at multiple locations and a microphone to capture the corresponding acoustic pressure fluctuations.

Our results show that during whistling, a periodic vortex shedding emerges from the outer orifice, analogous to the lips, and the frequency of these flow oscillations is identical to the frequency of the radiated sound, indicating a strong flow–acoustic coupling. We further investigate the influence of lip-like curvature at the outer orifice and find that it significantly affects the boundary layer separation and, in turn, the amplitude of the sound. The presence of smooth edges tends to attenuate or delay shear layer separation compared to sharp-edged orifices. Measurements within the resonant cavity also reveal a strong correlation between the amplitude of velocity fluctuations and sound pressure levels, confirming the presence of self-sustained oscillations.

These findings provide new physical insights into the flow features of human whistling, the mechanism of which has remained largely unexplained in the scientific literature. Beyond musical acoustics, understanding such flow-induced resonance in confined geometries has broader applications in the design of novel wind instruments and in controlling unwanted tonal noise in aerospace and mechanical systems involving orifices coupled to acoustic cavities.

Presenting Author: Prashanth Tamilselvam Illinois Institute of Technology

Presenting Author Biography: Prashanth Tamilselvam is a PhD candidate in Mechanical and Aerospace Engineering at Illinois Institute of Technology, Chicago. He holds a Master of Science (2020) in Mechanical and Aerospace Engineering from Illinois Tech and a Bachelor of Engineering (2017) in Mechanical Engineering from Anna University. He also has over 3.5 years of experience working in electronics manufacturing industry as a Manufacturing Process Engineer. His primary interests in academic research include fluid mechanics, acoustics, viscous flow stability and flow control. He has published research articles in SAE WCX world congress 2020 and AIAA SCITECH 2022.

Authors:

Prashanth Tamilselvam Illinois Institute of Technology
Francisco Ruiz ILLINOIS INSTITUTE OF TECHNOLOGY