2026-04-13 シカゴ大学（UChicago）
The Blob—a localized blob of turbulence created in a tank at the University of Chicago—is helping scientists better understand the laws of turbulent motion. Above, the motions that make up the Blob visualized through trajectories of tracer particles colored by speed.Image courtesy Takumi Matsuzawa
＜関連情報＞
- https://news.uchicago.edu/story/blob-tank-helping-scientists-tease-out-secrets-turbulence
- https://www.pnas.org/doi/10.1073/pnas.2526858123
- https://www.nature.com/articles/s41567-023-02052-0
静止流体中に広がる乱流塊の非線形拡散と減衰 Nonlinear diffusion and decay of a blob of turbulence spreading into a quiescent fluid
Takumi Matsuzawa, Minhui Zhu, Nigel Goldenfeld, and William T. M. Irvine
Proceedings of the National Academy of Sciences Published:February 12, 2026
DOI:https://doi.org/10.1073/pnas.2526858123
Significance
Turbulence, conventionally generated in the laboratory by continuously injecting energy into a fluid, is well understood as a cascade of energy from large to small scales where dissipation occurs. Yet predicting how turbulence spreads and decays once forcing stops remains a fundamental challenge. We create a compact “blob” of turbulence, isolated from boundaries by colliding vortex loops into the center of a still water tank, and track its evolution with unprecedented spatial and temporal resolution. We observe steep fronts separating turbulent and quiescent regions, dual power-law decay, and a persistent footprint of the cascade far into decay-captured by a minimal model of energy transport and dissipation. Our work provides a detailed narrative for the interplay between nonlinear diffusion and dissipation.
Abstract
Turbulence, left unforced, evolves under its own dynamics, invading surrounding quiescent fluid as it decays. A ubiquitous and familiar phenomenon, this fundamental aspect of turbulence has resisted the marriage of principled theory and experiment with no universal law yet capturing its evolution. Conventional flow chamber experiments have been hampered by boundary effects or strong mean flows that obscure the intrinsic dynamics of relaxation to quiescence. To circumvent these limitations, we create a spatially localized blob of turbulence using eight converging vortex generators focused at the center of a water tank, and observe its decay and expansion over decades in time using particle image velocimetry with logarithmic time sampling. The blob initially expands and decays until it reaches the walls of the tank and eventually transitions to a second regime of approximately spatially uniform decay. We interpret the turbulent dynamics as an interplay of nonlinear diffusion with associated steep fronts separating the turbulent and quiescent regions, and nonlinear decay, as described by the Kolmogorov–Barenblatt equation. We find direct evidence for this model within the expansion phase and decay phases of our turbulent blob and use it to account for the detailed behavior we observe. Our work provides a detailed spatially resolved narrative for the behavior of turbulence once the forcing is removed, and demonstrates unexpectedly that the turbulent cascade leaves an indelible footprint far into the decay process.
渦輪によって供給される孤立した乱流塊の生成 Creation of an isolated turbulent blob fed by vortex rings
Takumi Matsuzawa,Noah P. Mitchell,Stéphane Perrard & William T. M. Irvine
Nature Physics Published:11 May 2023
DOI:https://doi.org/10.1038/s41567-023-02052-0
Abstract
Turbulence is hard to control. Many experimental methods have been developed to generate this elusive state of matter, leading to fundamental insights into its statistical and structural features as well as its onset. In all cases, however, the material boundaries of the experimental apparatus pose a challenge for understanding what the turbulence has been fed and how it would freely evolve. Here we build and control a confined state of turbulence using elemental building blocks—vortex rings. We create a stationary and isolated blob of turbulence in a quiescent environment, initiated and sustained solely by vortex rings. We assemble a full picture of its three-dimensional structure, onset, energy budget and tunability. The incoming vortex rings can be endowed with conserved quantities, such as helicity, which can then be controllably transferred to the turbulent state. Our one-eddy-at-a-time approach opens the possibility for sculpting turbulent flows much as a state of matter, placing the turbulent blob at the targeted position, localizing it and ultimately harnessing it.
