By | November 18, 2023
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Advancing in exascale computational algorithms and models for multiscale atmospheric flows leads to new wind power structures and energy maximizing strategies in place previously not possible, explains Brooke Van Zandt at NREL. The models can contain and process two billion grid points, simulates the airflow around turbines in a large wind farm with unprecedented accuracy. Van Zandt describes how the new tools are used to manage highly turbulent low-level jet streams (LLJ) which behave in powerful and complex ways. LLJs lead to a significant increase in the load on the turbine blades, reducing power output and operating lifetimes. Without such solutions, derating the turbines (operating at a lower power level) during times of high turbulence is the usual strategy to preserve their lifetime but at the expense of net power.

Low-level jet streams, also known as low-level jets (LLJs), behave in powerful and complex ways that could affect many American lives and livelihoods. Winds blowing along the US coast affect the homes of over 128 million people; the same wind energy has the potential to bring a tidal wave of clean, renewable electricity to power these homes for decades to come.

To harness this renewable energy resource, states along the Atlantic coast have pledged to deploy nearly 20 gigawatts of wind energy by 2035, which will make wind a significant source of energy for the country’s most densely populated region. But understanding how LLJs behave can help unlock their full potential, and studying this unseen force has proven challenging for most researchers—until now.

With joint support from National Offshore Wind Research and Development Consortium and GE Offshore Windresearcher at General Electric Global Research Center (GE-GRC) and that National Renewable Energy Laboratory (NREL) studies the effects of LLJ behavior along the Atlantic coast on offshore wind farms to find critical insights for a burgeoning US wind energy economy.

These maps show turbine and capacity estimates for the Bureau of Ocean Energy Management’s North Atlantic Wind Energy Areas / SOURCE: Tufts University

Advances in exascale computational algorithms

“Site-specific high-hostility simulations of wind farms are typically outside the scope of the wind energy design process due to the great complexity of the science and computational modeling involved,” said Balaji Jayaraman, senior engineer at GE Research and principal investigator (PI) of this project. “But through advances in exascale computational algorithms and multiscale atmospheric flow models– powered by the US federal research labs including NREL and powered by the world’s leading supercomputing capabilities – we have been able to show the feasibility of new wind turbine constructions previously not possible.”

A research collaboration between NREL and the GE Global Research Center revealed how low-level jet streams affect wind farm performance / PHOTO: Nicholas Brunhart-Lupo, NREL

Damage from low level jet streams

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 case of expansion at sea. Specifically, the Atlantic coast is known for strong LLJs with jet noses at heights comparable to the larger wind turbines planned for offshore offshore installations. These turbines could experience LLJ-driven forces that can quickly drain their lifetime, lower their efficiency, and even cause turbine shutdowns. The high-fidelity simulations allowed coastal LLJ studies to also help researchers discover strategies to mitigate these LLJ effects.

The red lines in this diagram illustrate power losses across a wind farm due to the LLJ observed in the New York Bight region. The red lines in this diagram correspond to simulations with LLJ and blue lines are from simulations with an ideal wind profile / SOURCE: “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

“When we realized the opportunity to make a broad impact on offshore wind in the US, we were able to bring together some very capable scientists from GE Research and NREL in a short period of time,” said NREL researcher and project co-PI Shashank Yellapantula. “This team was able to achieve all the goals originally proposed as early as 2019.”

“This kind of public-private partnership allowed us to bring together the best minds in 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 collaboration is transformative and not just enabling insight into hidden potential problems but also consistent and feasible solutions. The enhanced power of this interdisciplinary, cross-industry collaboration cannot be overstated.”

Modeling of low-level jet stream effects

Solving today’s energy problems is about having the ability to capture, process and understand large amounts of data. That’s why NREL joined the multi-year, multi-year collaboration. The US Department of Energy’s (DOE’s) Exascale Computing Project (ECP) and Wind Energy Technologies Office (WETO) formed a critical starting point for the LLJ project.

“A project like the ECP, with so many connected sub-projects that push the boundaries of what is possible, can provide important transferable capabilities that can be leveraged immediately to solve problems in specific domains, such as LLJs along the US Atlantic coast, that are far beyond original goal, says Ray Grout, director of NREL’s Computational Science Center.

Unmatched accuracy

As the leading laboratory for ECP ExaWind projectNREL has spearheaded an effort to develop algorithms, computer science, and software that enable emerging accelerated computing architectures simulate the airflow around wind turbines in a large wind farm with unprecedented accuracy. With the support of ECP and WETO, NREL ensures that the ExaWind codes can simulates the complex fluid and structure 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 only exascale hardware but also moderate-sized GPU clusters that push the envelope for energy-efficient computing—is a cornerstone of LLJ analysis.

NREL’s OpenFAST is a full turbine simulation code that when coupled 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 effects of flow dynamics on wind farms.

(Researchers at NREL used data from 20-turbine array simulations conducted as part of a collaboration between NREL and the GE Global Research Center to study the effects of low-level jet streams on wind farm performance. Visualization by Nicholas Brunhart-Lupo, NREL. Text version)

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 the LLJ within a small five-turbine array and a large wind farm with 20 turbines spanning a region of 10 kilometers. This simulation contains 2 billion grid points was one of the largest ever done with ExaWind code and was enabled using a compute time allocation at Summit at the Oak Ridge Leadership Computing Facility (OLCF). This compute time grant was part of an Advanced Scientific Computing Research Leadership Computing Challenge grant 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 Summits 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 of collaborations that lead to important scientific breakthroughs.”

Reduces loads without compromising the net effect

From these simulations, the project team discovered that LLJ leads to significant increase in load on wind turbine blades. In addition, the wind profile observed in these coastal LLJs leads to deeper wakes (ie areas of reduced speed and increased turbulence) and thus reduced power from large wind farms such as those planned for the Atlantic coast.

This figure compares mean wind speed (top) and turbulent kinetic energy (bottom) from a wind farm simulation performed as part of this project. The images on the left are from simulations with LLJ and the images on the right are from simulations with an ideal wind profile / IMAGE: “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 data from these large-scale simulations, the team is now design real-world strategies to mitigate the effects of LLJ on turbine loads. Prior to this study, derating the turbines (ie operating at a lower power level) was a common strategy employed by major wind power developers; this leads to increased lifetime of wind turbines at the expense of the net effect. The strategies being developed by the NREL/GE Research team will reduce the load on turbines without compromising the net power output of wind farms.

“We’ve never had this level of detail available to us before to understand that wind farms that are designed in a certain way can withstand the force of LLJ phenomena,” Yellapantula said.

Apply science for fast, 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 project has helps manufacturers like GE Offshore Wind develop wind turbine control systems designed to improve wind turbine lifetimes.

“This project was a great example of an industry R&D team collaborating with a national lab team to take advantage of leadership computing at Oak Ridge National Laboratory,” Yellapantula pointed out. “All of these elements helped us examine complex scientific challenges affecting the US offshore wind industry.”

To realize a clean energy future for all, NREL sees public-private partnerships as the key ingredient for rapid and long-term transformation of the energy sector. As the US 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 groundbreaking discoveries in the renewable energy sector. Partner with NREL to address your renewable energy design and implementation challenges with world-class computing resources.

Read published journal article on this LLJ study.


Brooke Van Zandt is a communications specialist at National Renewable Energy Laboratory (NREL)

This article is published with permission from National Laboratory for Renewable Energy

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