College of Engineering, Computing and Applied Sciences

Answers to turbulence questions could be blowing in the wind


Chenning Tong of Clemson University is leading a new collaborative project that he said could answer questions about atmospheric turbulence that have confounded researchers for decades while laying the groundwork for advances in fields ranging from wind energy and weather forecasting to air pollution control.

Tong, a professor of mechanical engineering, said a $2.2-million grant from the National Science Foundation will allow him to further develop and test his theory about turbulence, the last unsolved problem in classical physics.

Headshot of Chenning Tong in a bright hallway.
Chenning Tong is receiving a $2.2-million grant from the National Science Foundation that will allow him to further develop and test his theory about turbulence, the last unsolved problem in classical physics.

He is using a new approach to fundamentally revise the Monin-Obukhov similarity theory, which he said was successful when first proposed in 1954 but has since been found to have major shortcomings. The theory, for example, can predict average wind speed but not wind fluctuations near the ground, he said.

Tong is calling his new theory the multi-point Monin-Obukhov similarity theory and said it is able to predict wind fluctuations and other properties of the atmospheric turbulence that the original fails to predict.

“I’m very excited on two different levels,” Tong said. “One is that a number of important applications are going to benefit, but also on a theoretical and intellectual level, it’s a much more satisfying theory.”

Atul Kelkar, chair of the Department of Mechanical Engineering, said Tong is well positioned for success.

“This collaborative federal grant will allow Dr. Tong and his partners to help answer questions that have perplexed researchers for decades,” he said. “Dr. Tong is pioneering a new theory. With his years of knowledge and experience, he is ideally suited to lead this project.”

Researchers have been trying since the early 1970s to overcome limitations of the Monin-Obukhov similarity theory, Tong said. His team had a breakthrough in 2015 while analyzing 2008 data it had gathered in California’s Central Valley.

Tong said the team gained physical insights into wind fluctuations that were missing in the original theory and that the findings led him to propose the multi-point Monin-Obukhov similarity theory. He reported the results in 2018 in a plenary talk at the American Meteorological Society’s 23rd Symposium on Boundary Layers and Turbulence.

“The new theory succeeded in overcoming the limitations of the original theory and greatly improved the understanding of the atmospheric boundary layer,” he said.

The atmospheric boundary layer is a turbulent area that during the daytime extends about 1-2 kilometers up from the Earth’s surface. The turbulence in it is created by wind and plumes caused by solar radiation and has a major effect on the weather and many other atmospheric phenomena.

Tong said that as part of the new project, he and his team will return to California’s Central Valley in 2023 to take field measurements on the atmospheric boundary layer in a farm field. The measurements will allow his team to test and calibrate the multi-point Monin-Obukhov similarity theory, he said.

It will be a big operation, with wind, temperature and velocity measurements taken by drone, lidar and radar, to name a few examples.

“We have all the instruments we can think of and have access to for this testing,” he said. “We’re going to be in the hot sun for eight weeks. From those measurements, we’ll be able to gather enough data to essentially calibrate the coefficients in the theory.”

A greater understanding of wind fluctuations could help predict wind turbines’ output, disperse airborne pollutants and improve numerical weather forecasts, he said.

Four graduate students, six undergraduates and a postdoctoral researcher will assist with the project.

“It’s going to be really exciting for them, and they are going to work on the cutting edge,” Tong said. “They are going to bring that knowledge to whatever they do after graduation. They could go into academia, national labs or companies.”

For Tong, the development of the theory has been more than a quarter century in the making. He first started researching atmospheric turbulence in 1995 as a postdoctoral researcher.

“The development of the new theory has been a long and sometimes difficult but always rewarding intellectual journey for me,” Tong said. “During this time, I have received strong support from the mechanical engineering department, the college and the University, for which I am grateful.”

Among those offering their congratulations on the grant was Tanju Karanfil, vice president for research at Clemson University.

“This is an outstanding accomplishment,” he said. “It is a clear recognition of Dr. Tong’s leadership in the field, and it is exciting research with many implications. I am so happy for Dr. Tong’s well-deserved success. “

Anand Gramopadhye, dean of the College of Engineering, Computing and Applied Sciences, said that Tong’s grant is well deserved.

“The amount of funding is a testament to the level of scholarship that Dr. Tong brings to the college,” Gramopadhye said. “His work underscores not only the excitement of new discoveries but also the potential of those discoveries to lead to innovation with real-world impact. I offer him my wholehearted congratulations.”

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