Numerical calculation of flow resistance for agglomerates with different morphology by the Lattice–Boltzmann Method

• Fully-resolved direct numerical simulation of the flow about compact and dendritic agglomerates by Lattice–Boltzmann Method.
• Local mesh refinement and curved wall boundary conditions for enhancing the agglomerate spatial resolution and reducing computational cost.
• Discussion of agglomerate properties and morphology resulting from generation algorithm.
• Comparison of volume and area equivalent diameters as basis of calculating agglomerate resistance.
• Projected cross section of convex hull around the agglomerate yields almost identical drag coefficient for all considered agglomerate morphologies.

Agglomerated particles appear in various areas of process industry in the form of products, waste or contamination. In this work, the Lattice–Boltzmann Method (LBM) is used to perform high resolution simulations for investigating forces on agglomerates depending on flow conditions and agglomerate structure. This paper presents an approach to generate and characterize three-dimensional agglomerates and to predict the flow around these aggregated structures using a 3D LBM with local grid refinement. The considered agglomerates are composed of spherical primary particles which are connected to each other by rigid joints. The characterization of the agglomerates is done using common equivalent diameters as well as the fractal dimension and the convex hull. Simulating the flow field around the agglomerates leads to the forces and torques acting on the primary particles. From that the drag, lift and torque coefficients are determined and their dependence on agglomerate structure, orientation and flow conditions is analysed. The coefficients were evaluated for different compact and dendritic agglomerates by using relevant projected cross sections and equivalent diameters. It could be demonstrated that when using the projected cross section of the convex hull perpendicular to the flow direction, the drag coefficient is almost independent on agglomerate morphology and orientation. Using the volume equivalent sphere yields wrong drag coefficients which completely deviate from standard correlations. This will now allow accurate numerical calculations considering point-particles, e.g. by the Euler/Lagrange approach. As agglomerates are mostly quite small the majority of simulations was conducted for a Reynolds number of Re = 0.3. In order to confirm the findings also for higher Reynolds numbers some simulations were done for Re up to 10.

Figure optionsDownload as PowerPoint slide