3262 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 59, NO. 12, DECEMBER 2010
Long-Duration Time-Resolved PIV to Study
Unsteady Aerodynamics
Zachary J. Taylor, Roi Gurka, Gregory A. Kopp, and Alex Liberzon
Abstract—A time-resolved particle image velocimetry (PIV)
system has been developed at the University of Western Ontario,
London, ON, Canada, with long-recording-time capabilities. This
system is uniquely suited to the study of unsteady aerodynamics
and hydrodynamics, such as avian aerodynamics or bluff-body
oscillations. Measurements have been made on an elongated bluff
body through the initial build-up phase of flutter. The possibilities
to study this instability, which was responsible for the collapse
of the Tacoma Narrows Bridge, are significantly broadened by
the use of this system. The long-time recording capability of the
system allows for novel results since it yields data that are spatially
and temporally resolved over a long record length. The buildup
of flutter is shown to exhibit complex dynamics that are heavily
influenced by the flow-induced motion of the body. Features of the
wake turbulence as a function of time are presented and shown to
substantially vary.
Index Terms—Image processing, open-source software, optical
velocity measurement, particle image velocimetry (PIV), unsteady
aerodynamics and hydrodynamics.
I. INTRODUCTION
THERE are many examples in engineering practice andnature where fluid flows are both turbulent and unsteady
in the time-averaged sense. Two natural examples of these cases
are oceanic flows, where turbulence is modulated by waves and
tides, and avian aerodynamics, where turbulent flow simulta-
neously exists with the unsteady vortices generated by flap-
ping wings. Among engineering applications, one of the most
famous engineering disasters—the Tacoma Narrows Bridge
collapse—is an example of these types of flow conditions as
it failed due to bluff-body flutter. The current state-of-the-art
techniques are not suitable for measuring these phenomena due
to the lack of either temporal/spatial resolution or the lack of
long-time recording capabilities.
Manuscript received September 14, 2009; revised February 6, 2010;
accepted February 8, 2010. Date of publication May 17, 2010; date of current
version November 10, 2010. This work was supported in part by the Canada
Foundation for Innovation, by the Ontario Research Fund, and by the University
of Western Ontario to develop the Advanced Facilities for Avian Research
under the leadership of Dr. S. MacDougall-Shackleton. The work of G. A. Kopp
was supported by the Canada Research Chairs Program. The Associate Editor
coordinating the review process for this paper was Dr. George Xiao.
Z. J. Taylor and G. A. Kopp are with the Boundary Layer Wind Tunnel
Laboratory, University of Western Ontario, London, ON N6A 5B9, Canada
(e-mail: ztaylor@uwo.ca; gakopp@uwo.ca).
R. Gurka is with the Department of Chemical Engineering, Ben-Gurion
University of the Negev, Beersheva 84105, Israel (e-mail: gurka@bgu.ac.il).
A. Liberzon is with the Turbulence Structure Laboratory, Tel Aviv Univer-
sity, Tel-Aviv 69978, Israel (e-mail: alexlib@eng.tau.ac.il).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TIM.2010.2047149
Bluff-body flutter has been a persistent problem for bridge
engineers. As previously noted, the most well-known case of
bluff-body flutter is the collapse of the Tacoma Narrows Bridge.
Although often interpreted as resonance between alternating
vortices in the wake, it has definitively been shown that it was
flutter that caused the bridge to collapse [1]. This distinction
is important because the vortices being shed from the body,
as well as the turbulence created by the unsteady flow around
the body, have time scales much shorter than that of the os-
cillating bridge. Since the engineering community witnessed
this catastrophic failure, steps have been taken to understand
and prevent this instability. Currently, an experimental method
similar to that developed by Scanlan is required to gauge a given
bridge’s stability [2]. This section model technique has been
used in wind engineering for every long-span bridge in the last
40 years and is still used today in the Boundary Layer Wind
Tunnel Laboratory (BLWTL), University of Western Ontario,
London, ON, Canada, and other leading facilities. However,
due to the lack of experimental tools, the understanding of
this instability is still quite limited. Over the years, many
researchers have looked at this instability by surface pressure
measurements and structural responses (e.g., [3]). However,
with the large amplitude of body motions, it becomes difficult
to extract information about the flow from surface pressure
measurements as the motion-induced pressure field dominates
and structural responses give no information about features of
the flow.
With the advent of particle image velocimetry (PIV), it
became possible to learn more about flow fields such as these.
PIV has been an established technique in the fluid mechanics
community for some time (e.g., [4]) but has seen little use in
wind engineering. Work has been done on the near wake during
this instability using classical (no-time-resolution) PIV tech-
niques [5]. Even with time-resolved PIV (TR-PIV), however,
it would be impossible to measure the buildup of flutter from
incipient motion to motions of large amplitude. Thus, a new
PIV system has been developed at the University of Western
Ontario, which allows for resolution in time, paired with the
capability of long recording periods. This novel system will be
used to measure various problems in unsteady aerodynamics
and hydrodynamics.
Typical in unsteady aerodynamics and hydrodynamics is
some low-frequency component significant to the flow (such as
the flapping of wings or a bluff-body oscillating), as well as the
higher frequencies associated with turbulent fluid motion. This
streaming TR-PIV (STR-PIV) system has the unique ability to
capture many cycles of the low-frequency features, as well as
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