image: FORMATION AND EVOLUTION OF TURBULENT SPOTS IN BOUNDARY LAYERS (From the promotional poster by Cambridge University Press for Cunbiao Lee's article published in JFM）
Credit: ©Cambridge University Press
Turbulence, famously described by Richard Feynman as “the last unsolved problem of classical physics”, pervades almost all natural and engineering flows. The century-old challenge of turbulence research centers on two key questions: how turbulence originates, and how it evolves.
The research team led by Professor Cunbiao Lee at the State Key Laboratory for Turbulence and Complex Systems, Peking University, provides a comprehensive review of recent progress in uncovering the origin of turbulence. In a National Science Review article, the article highlights the universal “soliton-like coherent structures” (SCS), play the dominant role in the generation of turbulence. The discovery of SCS has led to a new framework that clearly describes the entire boundary-layer transition with different paths. For the K-type transition, the discovery of SCSs, compared with the classical results of Morkovin and Kachano, offers the most comprehensive and clear picture of turbulence developments. These findings further confirm that SCS are not only limited to the boundary-layer transition but also occur in pipe flows, stratified flows, jets, falling films, wakes, etc., indicating a universal mechanism governing the laminar-to-turbulent transition.
“This study reveals a concise and unified physical process under complex flow conditions,” says Prof. Cunbiao Lee, the corresponding author of the article. The review also clarifies how the SCS are related to, and extend classical theories of turbulent generation. It indicates that, unlike the well-known traveling wave, the SCS serve as the fundamental building block of turbulence. These findings provide a much clearer path towards understanding the physical origin of turbulence.
“As the saying goes, ‘…. a craftsman who wants to do his job well must first sharpen his tools…….’,” the authors highlight the critical need for advanced experimental techniques and data-processing methods in turbulence research. They note that near-wall measurements often reveal unexpected flow structures, and that incomplete data can lead to misconceptions or even misdirections. The authors suggest some key new directions in turbulence research that are relevant to important concepts such as turbulent spots, low-speed streaks, and turbulent drag reduction.
About the study
This work, titled “Soliton-like coherent structures: a key to opening the door to turbulence,” appears in an upcoming 2025 issue of National Science Review. The authors are: Chinese Science Academician Shiyi Chen, Chinese Science Academician Xiaogang Deng, and Professor Lee of Peking University. The State Key Laboratory for Turbulence and Complex Systems is a leading research center dedicated to fundamental studies of turbulence. Current research in this lab involves turbulence and complex systems via theoretical, experimental, and computational simulations to enhance our understanding and control of turbulent flows.