Numerical study and analysis of the effects of recirculation flow rates in drained pebble flow

The effects of recirculation flow rates on the dense pebble flow (DPF) in a drained pebble bed are investigated through DEM simulation. After validation by experimental data, the velocity characteristics are analyzed and obvious intermittency characteristics are observed. The profile features and the shapes of the velocity distributions are estimated considering the flatness and symmetry for all flow rates. Fluctuation is estimated by the statistical parameter coefficient of variation and the newly proposed relative fluctuating kinetic energy (RFKE). Furthermore, the multi-fractal analysis of the velocity signals is carried out by the multiplicative cascade method (MCM). It has been found that the pebble flow follows the fractal phenomenon, and the intermittency of pebble flow has been measured quantitatively by the multi-fractal analysis. The increased flow rates always indicate smaller intermittency and higher frequency fluctuation, and vice versa. A new intermittency index C is proposed to quantitatively describe the intermittency of the DPF. The categorization of flow regimes of DPF has been discussed based on the analysis of combined parameters, i.e. the intermittency index C and relative fluctuating kinetic energy (RFKE).