What Engineers Can Learn From Owls' Stealthy Flight

May 03, 2020

Owl wings fluid flow

(Image credit: Roi Gurka, Costal Carolina University and Elias Balaras, GW)

Professor Elias Balaras of the Department of Mechanical and Aerospace Engineering and other teams of researchers across the country are conducting research on owls’ quiet flights to learn how their wing attributes can be adapted to silence wind turbines and airplanes. His work was referenced in this recent Smithsonian article

Balaras explains that his lab has been conducting research on biological fluid dynamics for over 20 years. “Within this field, our primary focus is to develop multiscale, multiphysics computational models for complex biological systems,” he says. 

A group led by Coastal Carolina University’s Roi Gurka approached Balaras to take part in their work, which involves “performing fluid flow experiments with live owls in a specially designed wind tunnel with the objective to identify the relation between the owl’s stealth and the flow induced by their flapping wings,” Balaras explains. 

“The topic is really fascinating and their experiments are unique,” he says. “We designed a research program that utilizes our computational models and their experiments in a synergetic manner to provide a look into the physics of this problem at a level of detail never achieved before. The computational model, among other things, serves as a platform to perform ‘numerical experiments,’ where one or more or the micro-features that are unique to the owls wing morphology can be switched on and off to observe the impact on sound generation.” 

In the lab, technological resources play a key role in studying and mimicking the owls’ movements. “We start with a CAD model of the same owl used in the experiments generated from a laser scanner,” Balaras states. “We then animate this model to fly exactly the same way as the owl in the experiments, utilizing movies from multiple cameras in the wind tunnel and advanced image registration techniques we developed. We then solve the differential equations governing the dynamics of the flow induced by the modeled owl. This is a problem with billions of degrees of freedom and is solved on powerful supercomputers utilizing thousands of processors.” 

It turns out that the bird’s unique physical characteristics are paramount to concealing noise.    “Our work has revealed that the downy coat covering the upper part of their wings plays an important role in manipulating the flow over the wing, which may be central to noise reduction,” Balaras explains.

With this initial research underway, what’s next for Balaras and his team? “We are currently working on developing similar computational models for hawks and other predators that are not stealth to identify differences and similarities to owls in terms of flight biomechanics,” he says. 

And the research being conducted yields key discoveries across various fields of study, Balaras notes. “This work has broader impacts in multiple areas, such as inspiring new strategies to reduce aerodynamic noise, or helping biologists better understand the role of flight biomechanics of owls and hawks and their distinctly different evolution over millions of years.”