Two University of Illinois experts in theoretical mechanics explore the origins of jet engine noise—without the screaming turbines.

Anyone who has lived under the flight pattern of a major metropolitan or regional airport can attest that constant exposure to jet engine noise is a serious problem. Numerous studies have shown that the relentless roar from a busy runway poses all sorts of threats to the health and quality of life of its nearby neighbors, from sleep disruption to low birth weight. The reverberations from jet engine noise can become so intense that they have even been known to cause metal fatigue in aircraft components.

Aircraft manufacturers have made tremendous strides in making jet engines quieter in the past several years by focusing on the shape of the nozzle, the outlet at the back of the jet engine where compressed air mixed with jet fuel is released to propel the airplane forward. However, these improvements are achieved through a time-consuming, expensive trial-and-error process that involves comparing the way different kinds of nozzles alter the flow of air through the engine, resulting in different noise levels.

Moreover, while the experimental apparatus may achieve the desired results, it can’t explain them. At NASA Glenn Research Center in Cleveland, Ohio, "researchers conducting the mechanical experiments have a table covered with different attachments to put on nozzles," explains Jonathan Freund, assistant professor in theoretical and applied mechanics at the University of Illinois. "They try one after another, and if one works, they're happy. They don't know why; they don't know if it's the best they can do."

Production of noise from a jet nozzle. Freund and Wei focus on the near-nozzle area magnified in the inset, where the noise is most sensitive to small changes. (click on the image to enlarge)

However, what currently can't be easily determined directly from mechanical trial-and-error experiments very well could be simulated, and that's precisely what Freund and his graduate student, Mingjun Wei, are doing. Using a code that Wei has written and that forms the basis of his dissertation, Freund and Wei are using NCSA's Origin2000 and Platinum Linux cluster to clarify the nature of the mechanism of aerodynamic noise by working backwards. Work is underway to run the problem on the Titan cluster and the new IBM p690 system called Copper.

Access Online | Posted 9-23-2003