Low-level jet streams, also known as low-level jets (LLJs), behave in
powerful and complex ways that can impact numerous American lives and
livelihoods. Winds that blow along the U.S. coastline hit the homes of
over 128 million people; that same wind energy has the potential to
bring ashore a tidal wave of clean, renewable electricity to power
these homes for more decades to come.
To harness this renewable energy resource, states along the Atlantic
coast have pledged to deploy almost 20 gigawatts of wind energy by
2035, which will make wind a substantial source of energy for the
nation’s most densely populated region. But
understanding how LLJs behave can help unlock their full potential,
and studying this invisible force has proved challenging for most
researchers—until now.
With joint support from the National Offshore Wind Research and
Development Consortium and GE Offshore Wind, researchers at the
General Electric Global Research Center (GE-GRC) and the National
Renewable Energy Laboratory (NREL) are studying the impact of LLJ
behavior along the Atlantic coast on coastal wind farm installations
to find critical insights for a burgeoning U.S. wind energy economy.
![](images/images_04_18_2023/pic12.jpg)
These maps show turbine and capacity estimates for the
Bureau of Ocean Energy Management’s North Atlantic wind energy areas.
Image
from Tufts University
“Site-specific high-fidelity simulations of windfarms are typically
beyond the scope of the wind energy design process due to the sheer
complexity of the science and computational modeling involved," said
Balaji Jayaraman, senior engineer at GE Research and principal
investigator (PI) of this project. "However,
through advances in exascale computing algorithms and models for
multiscale atmospheric flows—driven by the U.S. federal research labs
including NREL and powered by the world’s leading supercomputing
capabilities—we’ve been able to demonstrate the feasibility of new
wind turbine designs previously not possible.”
Using such cutting-edge simulations, the NREL/GE-GRC team’s LLJ
research study has revealed a propensity for severe wake-induced power
losses and increased loads on wind turbines in offshore deployment.
Specifically, the Atlantic coast is known for strong LLJs with jet
noses at heights comparable to the larger wind turbines planned for
coastal offshore installations. These turbines could experience LLJ-driven
forces capable of rapidly depleting their lifetimes, lowering their
efficiency, and even causing turbine shutdowns. The high-fidelity
simulations enabled coastal LLJ studies to also help researchers
discover strategies to mitigate those LLJ impacts.
![](images/images_04_18_2023/pic13.jpg)
Illustrating power losses across a wind farm due to
LLJs observed in the New York Bight region, the red lines of this
chart correspond to simulations with LLJs and blue lines are from
simulations with an ideal wind profile. Image
from "Wind
farm response to mesoscale-driven coastal low level jets: a multiscale
large eddy simulation study" by T. Chatterjee,
et al., in Journal
of Physics: Conference Series,
IOP Publishing
“Realizing the opportunity to make wide-ranging impact on offshore
wind energy in the United States, we were able to bring together, in a
short period of time, some highly capable researchers from GE Research
and NREL,” said NREL researcher and co-PI of the project Shashank
Yellapantula. "This team was able to accomplish all the goals
originally proposed back in 2019."
“This sort of public-private partnership allowed us to bring together
the best minds across the fields of computational science and wind
energy and leverage world-class modeling and simulation tools and
computational infrastructure,” said Rick Arthur, director of computing
at GE Research. "Such a collaboration is transformative, enabling not
only insight into hidden potential problems but also consequent and
viable solutions. The amplified power of this interdisciplinary,
cross-industry collaboration cannot be overstated."
Modeling Low-Level Jet Impacts
Solving today’s energy problems is a matter of having the ability to
capture, process, and understand large amounts of data. That is why
NREL joined in the multipartner, multiyear collaboration. The U.S.
Department of Energy’s (DOE’s) Exascale Computing Project (ECP) and
Wind Energy Technologies Office (WETO) provided a critical starting
point for the LLJ project.
“A project like ECP, with so many affiliated subprojects that push the
boundaries of what’s possible, can yield important transferable
capabilities that can be leveraged immediately to solve problems in
specific domains, such as LLJs along the U.S. Atlantic coastline, that
are well beyond the original goals,” said Ray Grout, director of
NREL’s Computational Science Center.
As the lead laboratory for the ECP’s ExaWind project, NREL has been
spearheading an effort to develop the algorithms, computer science,
and software that enable emerging accelerated computer architectures
to simulate the air flow around wind turbines in a large wind farm
with unprecedented accuracy. With the support of ECP and WETO, NREL is
ensuring that the ExaWind codes are capable of simulating the complex
fluid and structural dynamics of wind turbines and wind farms
operating in a turbulent atmospheric environment.
ExaWind’s atmospheric boundary layer simulation capability—ready to
run on not just exascale hardware but also moderate-size GPU clusters
that are pushing the envelope for energy-efficient computing—provides
a cornerstone for LLJ analysis.
NREL’s OpenFAST is a whole-turbine simulation code that, when merged
with computational fluid dynamics codes (Nalu-Wind and AMR-Wind),
creates a virtual wind flow simulation environment. This virtual
testing and simulation capability allows researchers to see the
invisible impacts of flow dynamics on wind farms.
![](images/images_04_18_2023/pic14.jpg)
Researchers at NREL used data from 20-turbine array
simulations performed as a part of a collaboration between NREL and GE
Global Research Center to study the effects of low-level jet streams
on wind farm performance. Visualization
by Nicholas Brunhart-Lupo, NREL
Using the ExaWind code,
Oak Ridge National Laboratory’s Summit supercomputer, and NREL’s Eagle supercomputer,
the NREL/GE Research team simulated the impact of LLJs within a small
five-turbine array and a large 20-turbine wind farm spanning a region
of 10 kilometers. This simulation containing 2 billion grid points was
one of the largest ever done with ExaWind code and was enabled using a
compute-time allocation on Summit at the Oak Ridge Leadership
Computing Facility (OLCF). This compute time grant was part of an
Advanced Scientific Computing Research Leadership Computing Challenge
allocation awarded to the team in 2021 and 2022.
“High-resolution, highly accurate simulations like those produced for
this LLJ study required a level of high-performance computing power
like Summit’s that only a few facilities in the world have,” said Suzy
Tichenor, director of OLCF’s industrial partnerships program. “This
type of resource-sharing will continue to be the critical backbone for
collaborations that lead to important scientific breakthroughs.”
Reducing Loads Without Compromising Net Power
From these simulations, the project team discovered that LLJs lead to
significant increase in loads on wind turbine blades. Additionally,
the wind profile observed in these coastal LLJs lead to deeper wakes
(i.e., areas of reduced velocity and increased turbulence) and thus
reduced power output from large wind farms like those planned for the
Atlantic coast.
![](images/images_04_18_2023/pic15.jpg)
This figure compares mean wind speed (top) and
turbulent kinetic energy (bottom) from a wind farm simulation
performed as a part of this project. The images on the left are from
simulations with LLJs and the images on the right are from simulations
with an ideal wind profile. Image
from "Wind
farm response to mesoscale-driven coastal low level jets: a multiscale
large eddy simulation study" by T. Chatterjee, et al., in Journal
of Physics: Conference Series, IOP Publishing
Using the data from these large-scale simulations, the team is now
designing real world strategies to mitigate the impact of LLJs on
turbine loads. Before this study, derating the turbines (i.e.,
operating at a lower power level) was a common strategy employed by
large wind farm developers; this leads to increased lifespan for wind
turbines at the expense of net power output. The strategies being
developed by the NREL/GE Research team will reduce loads on turbines
without compromising on net power production of wind farms.
“We’ve never had this level of detail available to us before to
understand that wind farms that are designed a certain way can
withstand the power of LLJ phenomena,” Yellapantula said.
Applied Science for Rapid, Real-World Solutions
NREL is one of the national laboratories in the United States that
focuses on both basic and applied research.
By creating greater understanding of LLJs and their effects on wind
turbines, this collaborative research project helps manufacturers like
GE Offshore Wind develop wind turbine control schemes designed to
enhance wind turbine longevity.
“This project was a great example of an industry R&D team partnering
with a national lab team to leverage leadership computing at Oak Ridge
National Laboratory," Yellapantula remarked. "All of these elements
helped us investigate complex scientific challenges impacting the U.S.
offshore wind industry.”
To realize a clean energy future for everyone, NREL sees public and
private partnerships as the key ingredient for rapid and long-lasting
energy sector transformation. As the U.S. offshore wind industry
prepares for exponential growth, these partnerships will shape the
success of renewable energy transitions.
NREL is uniquely positioned to find real-world applications for its
breakthrough discoveries across the renewable energy sector. Partner
with NREL to address your renewable energy design and deployment
challenges with world-class computing resources.
Read the published
journal article on this LLJ study.
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