CFD Analysis of Turbulent Fibre Suspension Flow

Vijay Shankar,Örjan Johansson,Lars-Olof Landström,A.w Lundberg ,Taraka Rama Krishna Pamidi

doi:10.3390/fluids5040175

Vijay Shankar, Örjan Johansson + Show 3 more

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https://doi.org/10.3390/fluids5040175

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Abstract

A new model for turbulent fibre suspension flow is proposed by introducing a model for the fibre orientation distribution function (ODF). The coupling between suspended fibres and the fluid momentum is then introduced through the second and fourth order fibre orientation tensors, respectively. From the modelled ODF, a method to construct explicit expressions for the components of the orientation tensors as functions of the flow field is derived. The implementation of the method provides a fibre model that includes the anisotropic detail of the stresses introduced due to presence of the fibres, while being significantly cheaper than solving the transport of the ODF and computing the orientation tensors from numerical integration in each iteration. The model was validated and trimmed using experimental data from flow over a backwards facing step. The model was then further validated with experimental data from a turbulent fibre suspension channel flow. Simulations were also carried out using a Bingham viscoplastic fluid model for comparison. The ODF model and the Bingham model performed reasonably well for the turbulent flow areas, and the latter model showed to be slightly better given the parameter settings tested in the present study. The ODF model may have good potential, but more rigorous study is needed to fully evaluate the model.

Highlights

The Intergovernmental Panel on Climate Change (IPCC) has concluded that the emission of greenhouse gases does have an effect on the climate and that the levels are the highest in history [1]
The fibres are coupled to the fluid momentum through the orientation distribution function (ODF)
From the modelled ODF, explicit expressions for all components of the fibre orientation tensors were derived, which were used to compute additional stress term that arises in the fluid momentum equations due to the presence of fibres

Summary

Introduction

The Intergovernmental Panel on Climate Change (IPCC) has concluded that the emission of greenhouse gases does have an effect on the climate and that the levels are the highest in history [1]. Achieving increased energy efficiency in the industry sector is highly relevant in contributing to the development towards a climate neutral society, as the use and supply of energy causes approximately 60% of the emission of greenhouse gases [3]. A crucial step to design and optimise sustainable and energy-efficient methods for the different processes used within the pulp and paper industry is understanding the flow of pulp suspensions. Fibre modelling is a complex physical problem and fibre suspension rheology depends on various parameters such as fibre concentration and fibre type, and the flow regime itself [4]. In flows of decaying turbulence, for instance, fibres form local concentrations of fibres sticking together, called flocs, which have an impact on the suspension rheology [6]. The decaying turbulence flow is the most common type of flocculating flow [4]

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