New class of turbulence in active fluids

Area of Science:

• Physics
• Fluid Dynamics
• Nonlinear Dynamics

Background:

• Turbulence is a fundamental phenomenon across scales, crucial in physics but complex due to nonlinear dynamics.
• Traditional research focused on Navier-Stokes flows, but extending to active systems like bacterial suspensions is increasingly vital.

Purpose of the Study:

• To investigate turbulence in active fluids using a continuum model extending Navier-Stokes equations.
• To analyze the interaction between Navier-Stokes nonlinearity and cubic nonlinearity from flocking theory.

Main Methods:

• Developed a continuum model for active fluids incorporating general symmetry terms.
• Employed combined numerical and analytical approaches to study energy spectra.

Main Results:

• Discovered that energy spectra at large scales show power laws that are not universal.
• Demonstrated dependence of these power laws on finite-size effects and physical parameters.
• Identified nonlinear self-organization as a key characteristic of turbulence in active fluids.

Conclusions:

• The interaction between quadratic and cubic nonlinearities in active fluids leads to novel, non-universal turbulent energy spectra.
• This study quantitatively explains the origin of these spectral properties.
• Active fluid turbulence represents a new class of turbulent flows with unique characteristics.