WUSTL engineer devises ways to improve gas mileage

In the summer of 2008, it became very expensive to fill up a gas tank when gasoline prices hit close to $4 per gallon. Transportation by road or air consumes fuel, which not only increases our dependence on foreign imports but also is a source of greenhouse gas emissions that impact climate and global warming.

A mechanical engineer at WUSTL is developing techniques that will lessen monetary pain at the pump by reducing the drag of planes, cars and trucks. Drag is an aerodynamic force that is the result of resistance a body encounters when it moves in a liquid or gaseous medium such as air. Reduction in drag means less fuel would be required to overcome the fluid resistance encountered by the moving vehicle.

Working with undergraduate and graduate students, Ramesh K. Agarwal, Ph.D., the William Palm Professor of Engineering, has successfully demonstrated that the drag of airplane wings and cars and trucks can be reduced by employing active flow control (AFC) technology.

The idea behind AFC is to deploy actuators on the surface of vehicles to modify the flow in a way that the overall resistance is reduced. Using computational fluid dynamics software, Agarwal has found that the actuators modify the flow, which results in drag reduction, which in turn reduces the fuel amount needed.

“The most promising actuators are the so-called synthetic jet or oscillatory jet actuators, which are embedded in the surface of the body (an airplane wing, for example) and essentially perform injection and suction of the fluid from the surface in a periodic manner,” Agarwal said.

The transonic drag of an airplane wing can be reduced by 12 percent to 15 percent with the incorporation of actuators — about 20-30 spaced optimally on the surface of the wing.

“One can use the genetic algorithms and artificial neural net algorithms to optimize the placement of actuators,” Agarwal said.

His students have recently applied the concept on cars and trucks and have achieved 15 percent to 18 percent reduction in drag by placing the actuators on the back surface of these vehicles. Although the technology has not yet been deployed on any commercially available vehicle, it is being researched and investigated by airplane and automobile companies worldwide.

“There are approximately 100 million cars and trucks on the road in the United States alone, and hundreds of millions more worldwide,” Agarwal said.

“Similarly, there will be a substantial increase in air transportation worldwide. AFC technology can play an important role in fuel conservation and reduction of greenhouse gas emissions,” Agarwal said.

Agarwal is one of the most decorated engineers in the United States and a fellow of 10 national science and engineering societies, including the American Association for Advancement of Science, American Physical Society, American Society of Mechanical Engineers (ASME), American Institute of Aeronautics and Astronautics (AIAA) and the Institute of Electrical and Electronics Engineers.

Agarwal will receive the James B. Eads Award from the Academy of Science of St. Louis April 30. It is the latest of several distinguished awards he has received in the past three years.

In 2007, Agarwal received the Gold Award from the Royal Aeronautical Society of the United Kingdom, an award given to fewer than five Americans in more than 50 years.

In 2008, he received the Aerodynamics Award from the AIAA for outstanding contributions to aerodynamics — the highest national award given in aerodynamics. In 2008, he also was the recipient of William Littlewood Award given jointly by AIAA and the Society of Automotive Engineers. Established in 1971, the award has only been given once before to a member of academia.

Agarwal received the Fluids Engineering Award in 2001 from ASME — the highest national technical award given in fluid dynamics.

In addition to his work with AFC technology, Agarwal is working for the U.S. Air Force to develop techniques to predict heat transfer and to design improved thermal protection systems for the next generation of space access vehicles.