Fluctuation forces in turbulence

Turbulence is a non-equilibrium system: it requires a constant input of energy to be sustained. Another non-equilibrium system is life: organisms require a constant intake of nutrients to subsist. If you have a bucket of water, how do you know whether something is alive inside or whether you are just looking at fluid turbulence?

This question is very hard to answer, and has many ramifications. Related to it, we tried asking how many classical non-equilibrium phenomena can be observed in turbulence. One of the things we have been able to show in our collaboration is that turbulent worms, i.e. structures where vorticity is congregated, cause fluctuation Casimir-like forces to arise between two parallel plates in turbulence. This is a feature of non-equilibrium systems, and has also been shown to be produced by active swimmers like bacteria. In a follow-up study, we investigated the effect of plate size and other parameters on the force.

A natural follow-up question to this research becomes: what other forces or phenomena which could potentially be produced by bacteria can be replicated by “ordinary” turbulence?