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November 8, 2002

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   Troy Anderson, (858) 822-3075 or


Researchers at the University of California, San Diego (UCSD) Jacobs School of Engineering have laid the theoretical groundwork for the use of tiny microelectromechanical systems (MEMS) which could be employed on aircraft wings and inside of jet engines to more effectively control fluid flows. By allowing more precise control of turbulent flows in these systems, these devices could potentially lead to fuel savings and increased performance. “Until recently, actuation and sensing technologies did not exist to tackle such problems,” says Miroslav Krstic, professor of control engineering in the School’s Mechanical & Aerospace Engineering Department.

Krstic’s latest book, Flow Control by Feedback: Stabilization and Mixing (Krstic & Aamo), published by Springer Verlag ( in October 2002, provides an in-depth description of use of MEMS and stands as a major contribution in the field of flow control. It offers a comprehensive analysis of current research on the topic, both at UCSD and elsewhere.

Having developed the computational models and control algorithms necessary to give life to these revolutionary devices, Krstic emphasizes the fact that MEMS technologies have a dual purpose with regards to flow control — they can be used to suppress or create turbulence depending on the application. “Sometimes turbulence is welcomed and sometimes it is a nuisance. For example, one wants to reduce turbulent drag over airplane wings for efficient flight, or enhance turbulence for improved fuel/air mixing in combustion chambers within jet engines.”

Placed on an aircraft’s wings, the magnetic micro-flaps, measuring one-third of a millimeter in length, could be electromagnetically lifted and lowered to reduce drag and limit turbulence. “The devices are driven by voltage or current - there are no moving mechanical parts,” explains Krstic. “This would allow them to be manufactured at an extremely small scale with a silicon microchip fabrication technique.”

Used in a jet engine’s combustor, tiny micro-jets would shoot air in or out of the chamber to more uniformly mix gas and air, thus leading to more efficient burning and less fuel consumption. Comprised of membranes that suck in air or blow it out, the micro-jets, like the micro-flaps would have no moving mechanical parts and rely on simple pressure sensors and feedback controllers to tell them when to operate.

Figure 1
Figure 2
Micro-jets within combustion engines homogeneously mix fuel and air for more efficient burning in the computer-simulated model based on control algorithms developed at UCSD. In Figure 2, the jets have been electromagnetically activated and mixing has occurred, in contrast to the solution in Figure 1, which remains relatively fragmented.

Essentially, the sensors would trigger the actuators which send a current to the electromagnetic components. Krstic notes: “These automated sensors are a critical component of the active feedback flow control system – one which brings functionality and adaptability to the MEMS devices. If the devices act too soon or too late, the situation is actually worsened and the benefits are lost.”

Krstic and his UCSD colleague, Professor Thomas Bewley, have laid the theoretical foundations for the utilization of these flow controlling MEMS devices by analyzing the underlying systems, developing the computational algorithms, and designing controllers with theoretical guarantees. “Now that these devices can be manufactured and implementation-ready controllers are available, feedback control of fluid flows is ready to enter the experimental stage,” says Krstic.


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