B. K. CRAWFORD ET AL.
Copyright © 2013 SciRes. OPJ
239
edges propagate along. This
st
of
obust method for
rbulent transition fronts in a wid
s without perturbing the flow.
e Air Force Re-
) through General Dynam-
as provided by AFOSR, the
REFERENCES
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Investigationsnic Boundary Lay-
istic lines that the turbu lent w
rongly selects for the wedge structure while suppress-
ing spurious noise and non-transition related features,
such as those caused by sun/shadows on the model. A
first guess is then made at the transition front by picking
the location with the largest result of this dot product at
each row in the image. This guess is then used to narrow
the region of the image where transition is believed to be
occurring. The reduced region is then re-evaluated,
searching for the strongest gradient. The process is re-
peated until this region is collapsed into a line, which
corresponds to the center of the high gradient region.
This line is then used to separate the image into laminar
and turbulent regions. The lamin ar region is then colored
red, while the turbulent region is colored blue. This,
when combined with th e earlier mentioned green chan nel,
results in the post processed image shown in Figure 10.
Finally, a chord scale is added to the image in black,
the median transition location is marked in purple, and
the median minus the median absolute deviation (MAD)
the transition location is marked in orange. All values
are presented in percent chord location. This provides a
robust and repeatable metric to quantify the transition
location that is not subject to the bias of a user manually
tracing transition fronts. Work is currently ongoing to
obtain additional quantitative data from these images
such as frequency content of the chordwise streaking due
to the influence of crossflow vortices.
6. Conclusion
IR thermography provides a fast and r
imaging laminar-tu
riety of environmente va-
The
quality of the results is on par or better than the industry
standard of naphthalene flow visualization, and requires
only a small fraction of the time. Additionally, IR ther-
mography responds to ch anging conditions in well under
a second. Lastly, IR thermography data can be post pro-
cessed into quantitative transition fronts.
7. Acknowledgements
Funding for SWIFTER is provided by th
search Laboratories (WPAFB
ics IT. Funding for SWIFT w
AFRL under the AEI program, and the Northrop Grum-
man Corporation. The authors would like to acknowl-
edge our test pilots, Roy Martin, Dr. Donald Ward, Dr.
Celine Kluzek, Lee Denham, and Lt Col Aaron Tucker;
the staff of the Oran W. Nicks Low Speed Wind Tunnel,
the Klebanoff-Saric Wind Tunnel, and the Texas A&M
Flight Research Lab; and our A&P Mechanic, Cecil
Rhodes.
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