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, [email protected]
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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, [email protected]
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