Turbine engines equipped with bearings that do not require oil lubrication can operate at higher temperatures, reduce maintenance costs and increase efficiency.
Daejong Kim, associate professor of mechanical engineering at The University of Texas at Arlington, recently received a three-year grant worth nearly $1.5 million from the Office of Naval Research to continue development of foil bearings for use in small engines used in aerospace applications. The project partner is Rolls Royce, which will determine the size of the engine and operating conditions consistent with Navy needs.
Eventually, Kim hopes to develop scalable design laws for foil bearings in small engines to power drones, helicopters and missile propulsion systems.
“I’ve been working to develop a new bearing system that doesn’t rely on oil since I began my career nearly 20 years ago, and the progress we’ve made so far is excellent,” Kim said. “Although the technology isn’t there yet to apply this to large machines, this research could be a big step toward that eventual use.”
Foil bearings are a type of aerodynamic bearing used in temperatures ranging from cryogenic to more than 650 degrees Celsius. The bearings consist of bump foils and top foils contained within a sleeve. As a shaft spins at high speeds, pressure builds and creates a hydrodynamic force within the air or gas between the spinning shaft and the stationary foils, supporting the shaft.
One of the challenges of traditional air/gas bearings is that the shaft becomes unstable at high speeds and can cause catastrophic damage to the entire system. The advantage of foil bearings is that they produce enough kinetic friction to avoid instability of the shaft at high speeds.
One of the breakthroughs achieved by Kim’s research team is that hybrid foil bearings increase load capacity dramatically compared to traditional foil bearings. The dramatic improvement of load capacity and rotordynamic performance are important milestones to an oil-free turbomachinery program in the Department of Defense.
Kim’s research has potential implementation across a broad class of engines, says UTA Mechanical and Aerospace Engineering Department Chair Erian Armanios.
“Dr. Kim has devoted his passion over the years to advancing foil bearing technology,” Armanios said. “His latest hybrid foil bearing design breaks the load-capacity barrier.
“This grant, a credit to his experience and standing, is an exciting opportunity for him to develop cost-effective solutions at various scales. His work would allow greater flexibility for the Navy and industry in the design of engines for new applications.”
– Written by Jeremy Agor, College of Engineering