UW team discovers a new law of physics

UW researchers have discovered a new law of fluid mechanics, a branch of physics, that will affect the future of aircraft design. The “Law of Incipient Separation” defines the maximum slope of an aircraft fuselage to avoid the separation of airflow that increases pressure-drag.

Getting the slope of the aircraft’s body right will reduce the drag and create a more efficient aircraft as far as fuel consumption. In a new paper, Aeronautics & Astronautics Associate Professor Antonino Ferrante, research assistant Dawei Lu, ’19, and doctoral student Abhiram Aithal define the parameters of this newly-discovered law.

“When the flow gets close to separation, the drag actually goes down, so the best scenario is to be as close to separation as possible without crossing the line because peak performance in control and efficiency is right before separation,” explains Aithal.

Ferrante had an intuition that the law existed. “Nature follows laws that are just waiting to be discovered,” he says. And Dawei and Abhiram worked out the simulations and data-analysis to prove it.

The process of proving the law’s existence involved researching aircraft fuselage geometry from NASA in fluid mechanics literature. This geometry is an analytical model used to run computer simulations of aerodynamics. The researchers first ran simulations with varied heights using this single geometry to find the slope value where flow gets close to separation. Next, they ran hundreds of simulations for different geometries and flow parameters and filed a patent on these new geometries which will aid further research.

“What surprised us most,” Lu says, “was that the maximum slope of the aircraft body and not the maximum curvature or the shape of the curved surface dominates this phenomenon.”