Century-Old Turbulence Theory Challenged as KTH Supercomputer Simulations Reveal Inverse Energy Cascade in Fine-Scale Vortices

KTH Royal Institute of Technology researchers reveal that small vortices can create larger swirls, a breakthrough for aircraft and heart valve design.

By: AXL Media

Published: Mar 13, 2026, 5:33 AM EDT

Source: Information for this report was sourced from KTH Royal Institute of Technology

Revisiting a Centenary Mystery in Fluid Mechanics

The fundamental question of how turbulence begins has remained one of the most enduring puzzles in physics for over a hundred years. Traditionally, the scientific community has adhered to the "forward cascade" theory, which posits that large swirling motions in a fluid gradually break apart into smaller and smaller swirls until their energy dissipates. However, new computer simulations conducted at the KTH Royal Institute of Technology suggest that this process may be more complex than previously understood. By analyzing the interaction of vortices—the main flow structures driving turbulence—researchers have found evidence that energy can actually move in the opposite direction, from the smallest scales back up to the largest.

The Mechanics of the Inverse Energy Transfer

In a study published in Scientific Reports, Professor Johan Hoffman and PhD student Joel Kronborg utilized advanced numerical analysis to observe the behavior of counter-rotating vortices. Their simulation began with two large vortices that created a powerful "strain field"—a localized region where fluid is simultaneously stretched and squeezed. This intense physical pressure generated a multitude of extremely small vortices. Surprisingly, these fine-scale swirls did not simply disappear; instead, they reconfigured themselves into specific zigzag patterns. The collective motion of these tiny structures eventually produced flow on much larger scales, effectively reversing the traditional chain of energy transfer.

A Dual-Directional Theory of Turbulence

While the findings introduce a revolutionary perspective, Professor Hoffman emphasizes that they do not necessarily invalidate the established forward cascade model. Instead, the research suggests a hybrid reality where both mechanisms can occur simultaneously. In this newly identified process, energy is first transferred from large-scale structures to the finest possible scales before the direction of the transfer is reversed. This suggests that turbulence is a bidirectional phenomenon, where small-scale patterns act as a foundational building block for larger atmospheric or industrial flow structures, rather than just being a byproduct of their decay.