Extreme dissipation event due to plume collision in a turbulent convection cell

TL;DR

This study links large-scale flow reductions and plume collisions in turbulent convection to extreme dissipation events, highlighting the importance of long-term data for capturing rare turbulence phenomena.

Contribution

It reveals how transitions in large-scale structures trigger extreme dissipation events in turbulent convection, a connection previously not well understood.

Findings

Extreme dissipation events correlate with plume collisions and flow reductions.

Detection of rare dissipation events requires long-time simulations.

Flow transitions significantly impact small-scale turbulence extremes.

Abstract

An extreme dissipation event in the bulk of a closed three-dimensional turbulent convection cell is found to be correlated with a strong reduction of the large-scale circulation flow in the system that happens at the same time as a plume emission event from the bottom plate. The reduction in the large-scale circulation opens the possibility for a nearly frontal collision of down- and upwelling plumes and the generation of a high-amplitude thermal dissipation layer in the bulk. This collision is locally connected to a subsequent high-amplitude energy dissipation event in the form of a strong shear layer. Our analysis illustrates the impact of transitions in the large-scale structures on extreme events at the smallest scales of the turbulence, a direct link that is observed in a flow with boundary layers. We also show that detection of extreme dissipation events which determine the far-tail statistics of the dissipation fields in the bulk requires long-time integrations of the equations of motion over at least hundred convective time units.