Prediction of terminal velocity of fractal aggregates with IBM-LBM method

Abstract

The settling of well-characterised fractal aggregates has been investigated numerically. The Immersed Boundary Method coupled with the Lattice Boltzmann Method (IBM-LBM) was developed to fully solve the liquid flow passing through the porous aggregate. Aggregates with prescribed structures covering the large spectrum of fractal dimension were fabricated and the benchmark experimental data have been collected to extensively validate the numerical model. Subsequently, the settling dynamics of fractal aggregates in liquid in terms of orientation evolution, time dependent drag force and terminal orientation was investigated and correlated to their morphological characteristics. Different equations have been developed for predicting the terminal settling velocity of fractal aggregates. A correlation that only requires inputs of primary particle size and fractal dimension is proposed for predicting the terminal velocity of fractal aggregates. Deviations less than 7% were obtained when applying the model for aggregates with the primary particle size ranging between 1.5 mm and 5 mm. The model's applicability to small aggregates comprised of primary particles less than 1 mm has also been demonstrated and discussed.