The behaviour of elongated non-spherical particles in wall-bounded turbulent shear flows: Analysis, Modelling and Validation

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The transport of non-spherical particles in a fluid is found in many industrial processes and also relevant for environmental flows. Quite often these processes involve a confinement as, for example, in a mixing vessel, in pipelines and in separation devices. Generally, such processes are operated in the turbulent flow regime and exhibit strong shear layers. Numerical investigations for the design and optimisation of these processes are very attractive due to the involved low cost and the detailed insight into the relevant transport processes. However, so far mostly the particles are assumed perfect spheres.In order to allow a reliable numerical computation of these mentioned technical processes using a point-particle based Euler/Lagrange approach, the proposed project aims at a thorough extension of the modelling framework for elongated non-spherical particles, especially with respect to strong shear (inhomogeneous) flows, turbulence and wall interactions. The focus will be on pronounced elongated non-spherical particle shapes such as fibres and plates which are very challenging to accurately model in a point-particle approximation.For that purpose, a multi-scale approach will be adopted using particle-resolved direct numerical simulations (PR-DNS) for deriving appropriate resistance coefficients for the forces, torques, as well as particle-fluid interaction models. The obtained simulation results will be collected in a publically available database and validated by small-scale three-dimensional particle-resolved imaging experiments. Based on these studies the Lagrangian point-particle models will be developed and implemented in the available numerical frameworks. With respect to turbulence modelling, complementary RANS and LES approaches will be considered. Specifically, model developments are needed for the drag, added mass, Basset force and transverse lift forces due to shear and particle rotation as well as pitching torque and the torque caused by the rotation of the particles. All these forces will be also analysed by the PR-DNS with respect to their modification by the presence of walls and appropriate correlations will be derived. Especially in liquid flows with elongated non-spherical particles lubrication effects are expected to be quite important, having an essential effect on the near-wall orientation.Eventually, validation data for the point-particle Euler/Lagrange simulations need to be obtained through detailed experiments, using shadow imaging techniques to determine the fully-resolved behaviour of non-spherical particles in turbulent wall bounded shear flows. For that purpose, a three-dimensional imaging technique which simultaneously captures fluid flow and particle motion will be developed. The successful outcome of this research proposal will deliver knowledge and models which will enable accurate predictions of wall-bounded turbulent flows with elongated non-spherical particles for a wide range of relevant conditions.