Tech Briefs Magazine - May 2021 - 35

steered at the later portion of that stage,
so it is important to immediately know
the air density in the rarified flow regime, from about 80 kilometers and up.
When it enters that later portion, its
flight path angle gets fixed and the vehicle just descends; it is barely affected by
the direction of the wind.
There is often an assumption that
there exists a fixed model known in ad-

vance and control methods can be determined that lead the vehicle to land. It's
often not the case because due to the
speed and the impact with air, hypersonic
vehicles change shape slightly during the
flight and that changes their dynamics
during flight. There is no unified model
that describes the entire flight because
the dynamics change gradually over time.
With the new algorithm, using the maxi-

mal rate of change, that knowledge can
be exploited to create an estimate.
There are other fields to which this
knowledge can be applied such as in electro-surgery to predict the temperature
field during a surgical operation so that
the surgeon can know how deep the cut is.
For more information, contact University
of Illinois news at news@illinois.edu; 217333-1085.

Turbulence Model for Design of Aircraft Capable of
Handling Extreme Scenarios
This model can be used to design better aircraft without having to wait months for
supercomputer calculations.
Purdue University, West Lafayette, Indiana

o help design aircraft that can better
maneuver in extreme situations,
researchers have developed a modeling
approach that simulates the entire process of a vortex collision at a reduced
computational time. This physics knowledge could then be incorporated into
engineering design codes so that the aircraft responds appropriately.
The simulations that aircraft designers
currently use capture only a portion of vortex collision events and require extensive
data processing on a supercomputer. Not
being able to easily simulate everything
that happens when vortices collide has
limited aircraft designs. With more realistic and complete simulations, engineers
could design aircraft such as fighter jets
capable of more abrupt maneuvers or
helicopters that can land more safely on
aircraft carriers.
Engineers would still need a supercomputer to run the model but they would be
able to simulate a vortex collision in
about a tenth to a hundredth of the time
using far less computational resources
than those typically required for largescale calculations.
The model is a Coherent-vorticity-Preserving (CvP) Large-Eddy Simulation
(LES) capable of capturing complex
physics without having to wait a month
on a supercomputer. The researchers
conducted complex, large-scale computations to prove that the model is accurate. These computations allowed them
to create a more detailed representation
of the problem using more than a billion points. For comparison, a 4K ultrahigh-definition TV uses approximately 8
million points to display an image.

A new modeling approach allows engineers to simulate an entire vortex collision without needing
to do extensive data processing on a supercomputer. (Courtesy Purdue University/Carlo Scalo)

Building off of this groundwork, the
researchers applied the CvP-LES model to the collision events of two vortex
tubes called trefoil knotted vortices
that are known to trail the wings of a
plane and " dance " when they reconnect. It is very hard computationally to
simulate because it is an intense localized event that happens between two
structures.
The team processed data on the
thousands of events that take place
when these vortices dance and built
that physics knowledge into the model.

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They then used their turbulence model
to simulate the entire collision dance.
Engineers could simply run the readymade model to simulate vortices over
any length of time to best resemble
what happens around an aircraft.
Physicists could also shrink the model
down for fluid dynamics experiments.
The team is working with the Department of Defense to apply the CvP-LES
model to large-scale test cases pertaining
to rotorcrafts such as helicopters.
For more information, contact Kayla
Wiles at wiles5@purdue.edu; 765-494-2432.
35

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