ARCHER2 Calendar July 2025

Active turbulence in microswimmer suspension.

Dr Giuseppe Negro, ICMCS, School of Physics and Astronomy, University of Edinburgh

The colour represents the largest eigenvalue of the Q-tensor, that gives the degree of local microorganism alignment. Resolution: 512 Fourier modes in each spatial direction comprising in total 1.7*E+9 degrees of freedom.
The coordinated behaviour of living organisms, like the collective motion of bird flocks, has long fascinated scientists. These behaviours spurred the development of the new "active matter" field in physics. Active matter systems, like bacterial suspensions, use internal energy to move, producing chaotic patterns like jets and vortices at high densities. This phenomenon, called “active turbulence”, differs from traditional turbulence in Newtonian fluids and remains poorly understood.
Our research aims to quantify active turbulence by treating it as a non-equilibrium phase transition. We developed a 3D model with 13 spatial fields and up to 10 billion degrees of freedom, whose dynamics are numerically solved using Dedalus, a Python-based framework for pseudo-spectral methods. The Figure shows a 3D configuration, where the colour corresponds to the Q-tensor’s largest eigenvalue, representing microorganism local alignment. Using 512 Fourier modes for each dimension, this simulation ran on ARCHER2 for 48 hours on 128 nodes.

This image was published on the July page of the ARCHER2 2025 printed calendar.