Quieting the Jet`s Roar - Texas Advanced Computing Center
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Quieting the Jet`s Roar - Texas Advanced Computing Center
Quieting the Jet’s Roar NASA research on engine noise relies on Ranger to enable first of their kind simulations If you’ve ever lived near the airport, or sat in the back row of a 747, you know that jets are noisy. Today’s aircraft have many sources of noise, but among them, the clatter of the exhaust system is a prime contributor. The higher the speed of the jet, the louder the noise it generates. But with the help of supercomputers, the roar overhead will soon be softened. “Jet noise has been a subject of intensive research since early 1950s,” said Ali Uzun, a research associate, who works with Professor M. Y. Hussaini at Florida State University. “One way to minimize jet noise is to modify the turbulent mixing process using special control devices, such A picture of the computational grid on the SMC006 chevron nozzle surface. as chevrons. Since noise is a by-product of the turbulent mixing of jet exhaust with ambient air, one can attempt to reduce the noise by modifying the mixing process.” For decades, experimental testing was the only way to understand the underlying physics of turbulence. But such tests are expensive, time-consuming, and only capable of studying a few physical prototypes at a time. Increasingly, computational simulations are taking a leading role in the study of turbulent interactions. In aerodynamics, a chevron refers to a triangle-shaped protrusion at the end of the nozzle. A crown of four to six chevrons set around the end of the nozzle [see figure, left] has been shown to reduce turbulence, and consequently noise, as compared to “Properly validated computational the usual circular nozzle. Chevron-shaped simulations can provide a lot more useful nozzles are one of the most promising jet information about the problem of interest noise reduction devices, but it remains than physical experiments,” Uzun said. unclear why chevrons reduce noise, and “Also, computational simulations can be how their designs can be optimized to used to study many different designs minimize output. without actually building the physical models. Once the computer simulations Uzun uses the Ranger supercomputer at point out the most promising designs, the Texas Advanced Computing Center experiments can be performed only on (TACC) as a 21st century virtual wind- those few models of interest to confirm that tunnel, simulating the turbulence and noise they are indeed working as intended. This generated by virtual exhaust passing though saves time and money.” a virtual engine. However, as Uzun suggests, for simulations to be useful for prediction and design, researchers needed to prove that they could replicate real results with virtual models. Which is what Uzun and his colleagues set out to do. A picture depicting a two-dimensional cut through the jet flow. The picture visualizes the turbulence in the jet flow and the resulting noise radiation away from the jet. The dark solid line represents the control surface for the Ffowcs Williams Hawkings (FWH) method, which is a special technique that is used for calculating noise propagation to distances far away from the jet flow. To determine how a given design would react to high-speed jet exhaust, Uzun first created a computer model of the chevronshaped exhaust nozzle. This was then integrated into a parallel simulation code that calculated the turbulence of the air as exhaust was forced through the nozzle. Working with a grant from National Aeronautics and Space Administration (NASA), his research is answering fundamental questions about turbulence and noise, including how complex physical phenomena generate sound waves in a jet “Dr. Uzun’s computations of chevron exhaust flow, and how noise suppression nozzles are pushing the state-of-the-art in devices, such as chevrons, modify the way computational fluid dynamics (CFD) as exhaust mixes with air to reduce noise applied to turbulent aerodynamics,” said Nicholas J. Georgiadis from NASA Glenn levels. Texas Advanced Computing Center | Feature Story For more info, contact: Aaron Dubrow, Science and Technology Writer, aarondubrow@tacc.utexas.edu Page 1 of 2 Research Center, technical manager for the project. “While most other efforts using large eddy simulations for jet computations have typically used on the order of one to 10 million grid points, Dr. Uzun’s computations have used up to 400 million grid points, and as a result are capturing a broader spectrum of the turbulent flow than has been done previously. Such computations require the use of a massively parallel computer platform to handle the size of the computer model under investigation.” Uzun’ ‘first of their kind’ calculations were made by possible by the generous computer time allocations on [the National Science Foundation’s] TeraGrid resources. The group relied on HPC systems at the National Center for Supercomputing Applications (NCSA) and the Louisiana Optical Network Initiative (LONI), as well as at TACC, to compute their high-resolution nozzle simulations. In 2008, the project used more than eight million computing hours, and in 2009, it will use up to 15 million computing hours, making it one of the most computationally-intensive science projects on the TeraGrid. Recent papers by Uzun: American Institute of Aeronautics and Astronautics (AIAA) 2009-3194 paper, “High-Fidelit Numerical Simulation of a Chevron Nozzle Jet Flow,” presented at the AIAA Aeroacoustics Conference in Miami, May 2009. AIAA 2007-3596 paper, “Noise Generation in the Near-Nozzle Region of a Chevron Nozzle Jet Flow,” presented at the AIAA Aeroacoustics Conference in Rome, Italy, May 2007. (Accepted for publication in the AIAA Journal) Ali Uzun, research associate at Florida State University But Uzun’s test cases are only the first step of a long design optimization process. The arc of the research extends from validating their computational methods, to identifying the key physical factors responsible for noise generation, to designing a new engine that can significantly minimize exhaust noise. Ali Uzun’s research is funded by NASA. Aaron Dubrow Texas Advanced Computing Center Science and Technology Writer June 18, 2009 The group’s turbulence research has important ramifications for both military and civilian communities. Hearing loss is Performing numerical simulations of test one of the most pervasive and expensive cases for which there are experimental problems the military faces. Much of the measurements available, Uzun’s group hearing damage is caused by prolonged matched the physical results with a high exposure to jet noise, which could be degree of accuracy [see image, left, for side- alleviated with quieter engines (and better by-side comparisons]. According to Uzun, hearing protection devices, as discussed in the results prove that computer simulations an April TACC feature). now have the ability to closely match experimental data, while providing far But a more powerful impetus may come more detailed information about physical from the public where restrictions on processes. “This means that we have the noise pollution near airports have been capability to produce reliable predictions strengthening worldwide. The U.S. aviation that can be used with confidence in jet noise industry is a significant contributor to the research,” he said. nation’s economy, boasting annual sales in excess of $36 billion and providing nearly one million jobs. New noise reduction legislation has inspired manufacturers to produce quieter engines for more powerful planes on short order — a task with which NASA, TACC and the NSF TeraGrid are happy to help. A comparison of experimental (left) and simulated (right) data shows a close match between results. “One of NASA’s primary goals is to conduct and support scientific research that will help the U.S. aviation industry maintain its global competitiveness,” Uzun said. “Quieter engines will create more jobs in the U.S. and help the economy.” Texas Advanced Computing Center | Feature Story For more info, contact: Aaron Dubrow, Science and Technology Writer, aarondubrow@tacc.utexas.edu Page 2 of 2