Turbulence is one of the most captivating and notoriously complex phenomena in fluid dynamics, manifesting as chaotic, unpredictable fluctuations that disrupt smooth flow. This erratic behavior is responsible for the familiar turbulence felt during air travel, as air currents violently jostle an airplane. For centuries, scientists have sought to unravel the mysteries behind turbulence, which is notoriously difficult to characterize and predict. Recently, an innovative study from the Okinawa Institute of Science and Technology (OIST) has made a groundbreaking advancement by exposing a subtle coexistence of two distinct types of turbulence within a special class of materials known as complex fluids — specifically polymeric fluids.
Complex fluids differ markedly from simple Newtonian fluids such as water or air. These materials possess attributes that straddle those of liquids and solids, often due to the presence of long-chain molecules called polymers. Polymers impart elasticity and internal structure to the fluid, profoundly altering how it reacts to external forces and flows. Everyday substances like shampoos, ketchup, and hand sanitizers fall into this category, demonstrating the pervasive nature of polymer fluids in both industry and daily life. Despite their prevalence, the turbulent behavior of polymer fluids has remained elusive and inadequately understood due to the complex interplay of fluid inertia and molecular elasticity.
Historically, the scientific community treated turbulence as emerging in two distinct guises depending on flow conditions. The first and most recognized form is inertial turbulence, a consequence of the fluid’s inertia dominating the flow regime. This type is characterized by violent, large-scale chaotic motions commonly observed in air and water when they move rapidly. The second is elastic turbulence, a more recently identified and less intuitive phenomenon that emerges from the elastic stresses created by stretched polymer molecules within the fluid. Unlike inertial turbulence, elastic turbulence can arise in flows with minimal inertia — essentially slow and gentle stirring — causing the flow to become chaotic due purely to elastic instabilities.
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Until now, it was commonly assumed that inertial and elastic turbulence occurred exclusively under separate and well-defined conditions: inertial turbulence at high speeds and large scales, and elastic turbulence restricted to low velocities and small-scale flows dominated by polymer elasticity. However, OIST researchers have now upended this dichotomy by demonstrating that these two behaviors coexist simultaneously in polymeric fluids under turbulent conditions. Their pioneering work utilized high-resolution numerical simulations to delve deep into the dynamics of polymer fluids and revealed that turbulent flows are far richer and more complex than previously thought.
The breakthrough came through the use of state-of-the-art computational modeling capabilities that captured turbulent behavior across a vast range of spatial scales. By simulating polymeric fluid flow at unprecedented resolution, the research team discovered that inertial turbulence dominates at larger scales, driving chaotic motions familiar from classical fluid mechanics. Simultaneously, at the smallest sub-scales of the flow — scales previously inaccessible to detailed observation — elastic turbulence arises due to the polymer molecules’ elastic stresses. This coexistence means a single turbulent flow exhibits a dual nature, with the two turbulence types intricately interwoven depending on the observation scale.
Dr. Piyush Garg, the lead author, highlighted the computational challenges involved: “To capture the small-scale interactions where elastic turbulence emerges required highly detailed simulations beyond anything done before in this field. The computational resources necessary were immense, but essential to reveal this hidden phenomenon that eluded scientists for decades.” Such robust and finely-detailed modeling has only recently become feasible thanks to advances in numerical algorithms and high-performance computing infrastructure, enabling exploration into the complex multi-physics nature of polymer fluid turbulence.
The implications of this discovery are extensive. Firstly, it broadens the fundamental understanding of turbulence, a problem that remains one of the most influential and difficult in classical physics. The finding that elastic turbulence can infiltrate inertial flows reshapes how scientists conceptualize turbulence in polymer fluids and challenges prior simplified models that treated these states as mutually exclusive. This new perspective offers a unified framework bridging two previously disconnected fields of research in fluid dynamics and polymer science.
Practically, the insights gained into the dual nature of polymer turbulence could revolutionize industrial processes where control over fluid behavior is paramount. Industries ranging from chemical manufacturing and oil pipelines to biomedicine rely on polymer additives to manipulate flow properties like viscosity, drag, and mixing efficiency. Understanding how and where elastic and inertial turbulence overlap allows engineers to design better fluid systems, optimize performance, and reduce energy losses. In biomedical applications, such as drug delivery, these findings might improve the predictability and efficiency of how polymer-based carriers navigate complex biological environments.
Professor Marco Rosti, head of the Complex Fluids and Flows Unit at OIST and co-author of the study, emphasized the broader significance: “Our discovery bridges two distinct research areas and demonstrates the power of interdisciplinary collaboration. This is a testament to OIST’s environment where physicists, engineers, and computational scientists come together to tackle long-standing open problems.” Indeed, the ability to connect theoretical, computational, and experimental perspectives is key to advancing turbulence research, which has traditionally been fragmented across various subfields.
In addition to providing clarity on the elusive nature of polymer turbulence, this work sets the stage for future experimental validation and new theoretical developments. Researchers now have a precise hypothesis to test: that elastic turbulence is hidden within the fine-scale structures of inertial turbulent flows. Experimentalists equipped with high-resolution measurement techniques may be able to observe this coexistence directly, while theorists can work towards formulating models that capture this multiscale complexity.
This discovery also invites a reevaluation of previous experiments and industrial scenarios involving polymer flows. Cases where unexpected flow behaviors were observed might now be explained through the lens of simultaneous inertial and elastic turbulence. Importantly, the interplay of these two forms of turbulence adds a new dimension to turbulence control strategies, as interventions targeting one scale or mechanism might affect the other in unforeseen ways.
In summary, the OIST study has revealed that turbulence in polymeric fluids is not a straightforward either-or scenario but a nuanced coexistence of inertial and elastic turbulence across scales. This revelation expands the fundamental understanding of complex fluid dynamics and opens avenues for technological innovation wherever polymers interact with turbulent flows. By leveraging cutting-edge computational modeling and interdisciplinary insight, the team has uncovered a hidden layer of complexity that promises to redefine fluid dynamics research in the coming years.
Subject of Research: Not applicable
Article Title: Elastic Turbulence Hides in the Small Scales of Inertial Polymeric Turbulence
News Publication Date: 13-Aug-2025
Web References: http://dx.doi.org/10.1103/pbtf-rn7d
References: Rosti (2025), J. Fluid Mech., 1012, R5. CC BY-NC 4.0.
Image Credits: Rosti (2025), J. Fluid Mech., 1012, R5. CC BY-NC 4.0.
Keywords
Physics, Fluid dynamics
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