Distorting airflows on purpose
Drawing up exotic, environmentally friendly airliner shapes won’t do much good if no one has
an engine that can handle the distorted airflow. Henry Kenyon explains how a university team
built a device that promises to expose such engine incompatibilities and save scarce research
dollars in the process.
NASA is researching designs for nextgeneration commercial aircraft
through its Environmentally Responsible Aviation program, but there’s a
catch: Some of the engineering models require inlets that are bent to
match the shape of the plane’s wing
or fuselage. Others are recessed into
the fuselage or mounted above the
aircraft’s wings.
These engine and body configurations could improve fuel economy
and reduce engine noise, but they
come with a price. Serpentine or recessed inlets can cause airflow distortions. Mounting engines next to the
Airflow distortion in a serpentine inlet is illustrated by a computational fluid dynamics simulation.
As air flows through the duct, a counter-rotating twin swirl pattern develops near the top of the inlet.
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AEROSPACE AMERICA/MARCH 2015
fuselage or over a wing can subject
them to turbulent air. Engine designers need to know how these configurations will turn and swirl the air as it
passes through the inlet to the engine
turbine blades, so that they can predict whether these distortions are
likely to result in reduced engine per-
formance, unacceptable blade wear or
proving that specific jet engines can
Although advanced aircraft designs
an increased risk of the blades failing
tolerate the distortion produced by
have been around for decades, there
catastrophically. They can then get to
the inlets of their host aircraft. Streamwas a missing technological compowork designing out these incompatiVanes also might replicate airflow
nent — the ability to model airflow
bilities or better yet finding a way to
over propellers for fixed wing aircraft
distortions for maximum perfortake advantage of the distortions to
and helicopters. In fact, developers
mance advantages, Lowe says.
improve fuel efficiency.
say requests for 3-D-printed StreamDeveloping StreamVane was not
The trouble is, it would be costly
Vanes are beginning to pour in.
easy. For starters, the team needed to
and time-consuming to build all these
The devices allow engineers to
digitally represent the airflow of a
proposed inlets to scale and test them
rapidly model new engine configuraspecific inlet in three dimensions,
in wind tunnels with various engines,
tions and modify them to either miticalled a profile. This would require
make adjustments to the engines and
gate or take advantage of any airflow
precise measurements, which was
test them again.
Lowe’s specialty on the
Engineers at Virginia
StreamVane team. Virginia
Tech set out in 2009 to solve
Tech researchers used comthis problem with funds from
putational fluid dynamics
NASA as part of the ERA proand particle image velocimgram. The Virginia Tech enetry to track airflow and
gineers saw that the ERA dedistortions. PIV measuresigns showed promise, but
ments are made by seeding
“there were certain enabling
the flow with tiny liquid
technologies that weren’t
particles, explains O’Brien,
there,” says K. Todd Lowe, an
the principal researcher.
assistant professor at Virginia
These particles are usually a
Tech’s Department of Aerotype of dye that can be
space and Ocean Engineertracked visually. PIV meaing. One of the missing
sures how clouds of these
pieces was a low-cost way to
particles move during very
replicate airflow distortions.
small time intervals and
The Virginia Tech team
then uses that data to create
came up with a device called
an airflow model.
a StreamVane — a circular
Researchers initially
high-strength plastic screen
plugged their real-world unthat can be fitted over an enderstanding of these swirlgine inlet to produce the
ing, vortical airflows and
same airflow profiles as spe- A StreamVane replicates airflow distortions of specific inlet designs in a wind tunnel. their related mathematics
cific inlet designs. Each This one was made with a 3-D printer.
into computer simulation
StreamVane is made by an
software such as MATLAB,
industrial three-dimensional
CFX and CFD to model airprinter according to a digital design.
distortions. Money is saved that would
flow and distortion dynamics.
StreamVanes were developed and
otherwise be spent building a series of
A Virginia Tech mechanical engitested in Virginia Tech’s large wind
physical prototypes. StreamVanes can
neering masters student, Kevin Hoopes,
tunnel. The devices were installed on
also replace or be used together with
devised a “push button” technique for
the university’s PWC JT-15D jet turpressure screens, which have been the
exporting the airflow profiles into a
bine engines, which it maintains for
standard airflow tool, explains Walter F.
computer-aided design tool, says Lowe.
research purposes. Because the
O’Brien, a Virginia Tech professor of
Each StreamVane is designed within
StreamVanes are made in an industrial
mechanical engineering and the prothat tool so it can be printed in three
3-D printer, they can be made of algram’s principal researcher. The key
dimensions. At first, a small-scale
most any material. Researchers hope
difference is that pressure vanes do not
StreamVane is printed and tested in a
to make future StreamVanes from
produce airflow distortions, which is
small wind tunnel to make sure that it
spray-deposited titanium.
the main purpose of the StreamVane.
creates the desired distortions and airIf the results of ongoing design
The StreamVane team expects
flow patterns. “It’s just like any sort of
tests are good, ERA designers could
the technology to be a key part of
engineering program — there’s a layer
soon have a new, low-cost method for
designing next-generation aircraft.
of experimentation and testing prior to
AEROSPACE AMERICA/MARCH 2015 11
doing the full-blown applicathrusts, Lowe says. One is
tion,” Lowe says.
fundamental and applied reFor now, Virginia Tech
search toward better turbine
plans to use the StreamVane
fans. The school is also being
technology to focus on jet enapproached by industry and
gine and inlet research. “We
government to provide them
actually are going to change
with StreamVanes. For 2015,
our engines here, based on
the university has multiple
what we think we should
StreamVane orders from Boedo,” O’Brien says.
ing and NASA.
O’Brien contends that
Virginia Tech has copythe StreamVane technology
righted the StreamVane procould be very useful for
cess. The university will build
a StreamVane to order for labs
companies developing new
jet engines or airframes. For
and universities wanting to
example, if a company
use the technology. Several of
wanted to install or test a jet
the devices have already been
engine on a new airframe, a In a low-speed wind tunnel test, a StreamVane is mounted in a 6-inch-diameter
built. In the future, it may be
PVC pipe. An external motor can rotate the StreamVane to any angle.
StreamVane could be applied
possible that customers could
craft’s performance, says O’Brien.
to determine if there is distortion and
acquire the software to make StreamBesides supporting research, the
whether the engine will work with
Vanes on their own printers, “but we
StreamVane has turned out to be a
that distortion.
aren’t there yet,” O’Brien says.
Henry Kenyon
product that the university can supply
Handled properly, inlet airflow
hkenyon@hotmail.com
to customers. There are currently two
distortion can actually increase an air-
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