April 18, 2003
by Skip Derra
Partha Sarkar's research motivation is buildings that stand up better to
tornadic-type winds. Photo by Bob Elbert.|
Partha Sarkar wants to bring the winds of change to building codes. More
specifically, to construct buildings that have a better chance of
withstanding tornados and other wind-damaging events.
Sarkar, who holds the T.A. and Grace Miller Wilson Endowed Chair in
Engineering and is an associate professor of aerospace engineering and civil
engineering, will begin his quest modestly, by building a novel type of wind
tunnel in Howe Hall.
Wind tunnels traditionally are big, clunky frames of steel supporting large
rectangular air ducts. Within the air ducts resides a massive fan, which
circulates air in the confined, controlled environment of the tunnel. What
Sarkar has in mind is nothing like that.
His tornado and microburst simulator is cylinder-shaped, with a large
opening at the bottom and a nearly complete enclosure at the top. Within the
18-foot diameter wide steel cylinder will be a concentric 1-foot wide duct.
This duct will circulate vortexed (swirling) air that is pushed down from
the top, through the duct, into the opened bottom. The swirling air then
will be sucked up through the top, through a 6-foot diameter fan inside the
cylinder, essentially simulating a tornado from the bottom up. With a flip
of a switch, the same simulator will generate a microburst (powerful
In concert with this fresh wind tunnel design, the entire simulator will
move along a steel girder frame powered by a 5-ton crane. The result, Sarkar
said, will be a wind tunnel that can replicate a moving tornado or
microburst as it sweeps over a landscape -- in this case a landscape
populated with models of buildings.
"Our idea is to have a facility for the 21st century, one that takes wind
tunnels to the next level," Sarkar said.
The tornado and microburst simulator -- on which Sarkar is collaborating
with Fred Haan of aerospace engineering, Bill Gallus of geological and
atmospheric sciences, and Josh Wurman of BITNET Inc., Boulder, Colo. -- is
one of two wind tunnels Sarkar has designed and whose construction he will
oversee this summer.
The other facility, the aero/atmospheric boundary layer wind tunnel, will
have a more conventional design and will be one of the largest of its type.
It will produce winds in the traditional fashion, though at higher speeds
(up to 110 mph) than similar tunnels. It also will be able to produce
variable wind gusts, a feature not found in current wind tunnels.
Together, the tunnels form the Wind Simulation and Testing Laboratory that
will just about fill up the entire west-end leg of Howe Hall. The laboratory
also should fill in some of the holes in current tornado and wind research,
and, Sarkar hopes, affect building codes.
Simulating gales, gusts
Conventional wind tunnels produce "straight-line winds," which are most
useful in understanding the fluid-structure interaction between surfaces and
air, and important if you are designing airplanes or a more efficient
automobile. Test results from conventional wind tunnels also have been used
to develop building codes. But Sarkar said conventional tunnels may not
provide values that are truly representative of extreme wind events, like a
"Wind tunnels today can simulate straight-line winds very well, but that
isn't very representative of the winds of a hurricane, which has gusting
winds with large variations in wind direction or turbulence," Sarkar said.
"In a tornado, where the vortex is relatively small compared to a hurricane,
the rotating flow has a different effect on structures. It produces much
higher pressures, or loads, than what you would get with the straight-line
winds produced in a regular wind tunnel."
Knowing he can't perfectly reproduce something as complex as a tornado,
Sarkar said the new lab more faithfully will produce the major elements of
one. The new facility, for example, more accurately will simulate what
happens when a twister hits a building, producing the gale forces and high
pressures the building experiences. In addition, because the wind tunnel
moves the tornado, the actual simulation is more realistic.
Ultimately, Sarkar said his research could result in changes to building
codes, which he said do not really take into account the true wrath of a
tornado. That, he added, will ruffle some feathers.
"It will create controversy," he promises of the tornado simulator research.
"It will not make the construction people happy."
Yet, Sarkar thinks the stakes are high enough to warrant a new look at an
Each year, 80 lives are lost and $850 million in damage occurs in this
country due to natural disasters, he said. Of that, 70 percent is caused by
wind, and a large chunk of the wind damage is due to tornados.
"People keep saying we can't do anything about this. We can't design
buildings that are tornado-proof," Sarkar said. "I agree to an extent. But
we can't just sit back and not do anything about it.
"With this facility, we will be in a much better position so that maybe in
10 years we will have building codes that consider tornado and microburst
winds," he added. "If we don't start now, we won't get there."
Ames, Iowa 50011, (515) 294-4111
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