Dynamics of fibres in a turbulent flow field - a novel particle-level simulation technique

A particle-level simulation technique has been developed for modelling the flow of fibres in turbulent flow. A single fibre is conceived here as a chain of segments, thus enabling the model fibre to have all the degrees of freedom (translation, rotation, bending and twisting) needed to realistically reproduce the dynamics of real fibres. Equations of motion are solved for each segment, accounting for the forces that describe interaction with the fluid, the forces that describe contact with other fibres and those that maintain integrity of the fibre. The motion of the fluid is resolved as a combination of 3D mean flow velocities obtained from a CFD code and fluctuating turbulent velocities derived from the Langevin equation. A case of homogeneous turbulence is treated in this paper. In addition, the paper discusses issues related to numerical stability of the proposed model. The results obtained here show that fibre flocs can be created also in the absence of attractive forces. Inter-fibre contacts and the individual fibre features (such as flexibility and equilibrium shapes) are shown to govern the physics behind formation and breaking up of fibre flocs. Highly irregular fibre shapes and stiff fibres lead to strong flocculation. The modelling framework applied in this work aims at making possible a numerical model applicable for solving fibre flow problems at industrial scale.