Soft Matter and Complex Systems Seminar

Viscosity is a property that tells us how easy it is to cause flow in a fluid. For incompressible isotropic systems, the most well-known type of viscosity is the shear viscosity, which quantifies how much of the fluid's available energy dissipates when a symmetric velocity gradient is induced into the system. However, the situation differs in so-called chiral active fluids, which are manifestly out-of-equilibrium systems. Here, the fluid particles are set into motion by activity or uniform rotation of the system and are, therefore, characterised by a non-trivial angular momentum density. Consequently, the flow properties of such a fluid are not just described by the shear viscosity. There are additional so-called odd viscosity coefficients that do not contribute to viscous dissipation in a direct manner.

Because of the fundamental interest in this problem and recent experiments, we study such chiral active fluids in the creeping flow regime in more detail. In part 1 of the seminar (1 December), we show that the fundamental solution can be explicitly constructed without any approximation for stationary three-dimensional incompressible flow. Our calculations form the basis for solving more complicated flow problems and for constructing the theory of hydrodynamic interactions in chiral active fluids. In part 2 of the talk (8 December), we will demonstrate how we can use the Green's function to construct an analytical exact solution for the single-particle problem. Furthermore, we will then explicitly demonstrate that odd viscosity can contribute to viscous dissipation via alteration of the fluid flow.