Visco-elastic behaviour of suspensions of rigid-rod like particles in turbulent channel flow

Dilute suspensions of rigid elongated particles show visco-elastic behaviour if the particles are small enough to be affected by Brownian motion. The visco-elastic behaviour of such suspensions is investigated in turbulent channel flow. A direct numerical simulation (DNS) of turbulent channel flow has been used to compute Lagrangian time traces of the velocity derivative tensor, as experienced by small inertia-free particles. Along these paths, the viscous and elastic stresses of ensembles of Brownian fibres are computed by a stochastic simulation based on the rheological theory of dilute suspensions of elongated particles and fibres in Newtonian solvents. Average and R.M.S. stresses are computed for various combinations of aspect ratio and Péclet number as a measure for the influence of the Brownian motion. It is found that stress levels as well as R.M.S. of stresses rise quickly with aspect ratio of the particles. The visco-elastic contribution to the total stress level can be as large as 30% for small Péclet numbers showing that elastic effects can indeed take place in suspensions of rigid particles.