Turbulence model could help design aircraft capable of handling extreme scenarios
Engineers make it possible to simulate complete 'dance' of colliding
vortices at reduced computational time

Date:
January 21, 2021
Source:
Purdue University
Summary:
To help build aircraft that can better handle violent turbulence,
researchers developed a new model that allows engineers to
incorporate the physics of an entire vortex collision into their
design codes.



FULL STORY ==========================================================================
In 2018, passengers onboard a flight to Australia experienced a terrifying
10- second nosedive when a vortex trailing their plane crossed into the
wake of another flight. The collision of these vortices, the airline
suspected, created violent turbulence that led to a free fall.


==========================================================================
To help design aircraft that can better maneuver in extreme situations,
Purdue University 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, the
researchers said.

"Aircraft in extreme conditions cannot rely on simple modeling," said
Carlo Scalo, a Purdue associate professor of mechanical engineering with
a courtesy appointment in aeronautics and astronautics.

"Just to troubleshoot some of these calculations can take running them
on a thousand processors for a month. You need faster computation to
do aircraft design." Engineers would still need a supercomputer to
run the model that Scalo's team developed, 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 large-scale calculations.



==========================================================================
The researchers call the model a "Coherent-vorticity-Preserving (CvP)
Large- Eddy Simulation (LES)." The four-year development of this model
is summarized in a paper published in the Journal of Fluid Mechanics.

"The CvP-LES model is capable of capturing super complex physics without
having to wait a month on a supercomputer because it already incorporates knowledge of the physics that extreme-scale computations would have to meticulously reproduce," Scalo said.

Former Purdue postdoctoral researcher Jean-Baptiste Chapelier led the
two-year process of building the model. Xinran Zhao, another Purdue postdoctoral researcher on the project, conducted complex, large-scale computations to prove that the model is accurate. These computations
allowed the researchers to create a more detailed representation of the problem, using more than a billion points. For comparison, a 4K ultra high definition TV uses approximately 8 million points to display an image.

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.

This dance is extremely difficult to capture.



========================================================================== "When vortices collide, there's a clash that creates a lot of
turbulence. It's very hard computationally to simulate because you have
an intense localized event that happens between two structures that look
pretty innocent and uneventful until they collide," Scalo said.

Using the Brown supercomputer at Purdue for mid-size computations and Department of Defense facilities for large-scale computations, the team processed data on the thousands of events that take place when these
vortices dance and built that physics knowledge into the model. They
then used their turbulence model to simulate the entire collision dance.

Engineers could simply run the ready-made model to simulate vortices
over any length of time to best resemble what happens around an aircraft,
Scalo said.

Physicists could also shrink the model down for fluid dynamics
experiments.

"The thing that's really clever about Dr. Scalo's approach is that it
uses information about the flow physics to decide the best tactic for
computing the flow physics," said Matthew Munson, program manager for
Fluid Dynamics at the Army Research Office, an element of the U.S. Army
Combat Capabilities Development Command's Army Research Laboratory.

"It's a smart strategy because it makes the solution method applicable
to a wider variety of regimes than many other approaches. There is
enormous potential for this to have a real impact on the design of
vehicle platforms and weapons systems that will allow our soldiers
to successfully accomplish their missions." Scalo's team will use
Purdue's newest community cluster supercomputer, Bell, to continue its investigation of complex vortical flows. The team also is working with
the Department of Defense to apply the CvP-LES model to large-scale test
cases pertaining to rotorcrafts such as helicopters.

"If you're able to accurately simulate the thousands of events in flow
like those coming from a helicopter blade, you could engineer much more
complex systems," Scalo said.

This work was supported by the Army Research Office's Young Investigator Program under award W911NF-18-1-0045. The researchers also acknowledge
the support of the Rosen Center for Advanced Computing at Purdue, and the
U.S. Air Force Research Laboratory Department of Defense Supercomputing Resource Center, via allocation under the subproject ARONC00723015.


========================================================================== Story Source: Materials provided by Purdue_University. Original written
by Kayla Wiles. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Xinran Zhao, Zongxin Yu, Jean-Baptiste Chapelier, Carlo
Scalo. Direct
numerical and large-eddy simulation of trefoil knotted
vortices. Journal of Fluid Mechanics, 2021; 910 DOI:
10.1017/jfm.2020.943 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/01/210121131701.htm

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