Papermaking flows are extremely challenging for modelling and simulation, if one accepts their full complexity. A wide range of particles, including fibres, fibre fragments (fines) and fillers (non-organic particles), flow and interact with each other in a non-dilute suspension, a complex geometry and at a high flow rate. Different simulation approaches are reviewed from particle-level simulations, through meso-scale simulations to the full flow geometry of the papermaking line. Their application to papermaking and potential to provide fundamental understanding as well as direct process-optimization support are discussed.

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In papermaking process the base paper is formed by starting from low concentration suspension. Depending on process stage different models can be utilized for better understanding and performance of the process. A short general overview of fluid dynamics related to papermaking process is given as well as new approaches including fiber network modeling and continuum mechanical fracture simulations. The fluid dynamical results presented illustrated some paper machine wet end phenomena while the solid state modeling approaches can be exploited from drying section of a paper machine to the several converting processes.

Fibre orientation distribution is essential factor affecting the properties of produced paper. The fibre orientation distribution is mainly determined by the fluid dynamics in the wet-end and in the wire-section of the paper machine. In this work the fibre orientation probability distribution in the paper machine jet-to-wire impingement is studied using modelling. The model used in this work is based on diffusion-convection equation. In addition to the transport of the fibres due to the mean flow, the model includes flow induced rotation of the fibres and randomising turbulence effects. Thus, the purpose of the model is to estimate the effect of the flow dynamics on the development of the fibre orientation probability distribution.