Visualization on the turbulent structure and restructure characteristic in the wake of a packed bed reactor: PIV measurements and POD analysis

Packed structures are widely applied in crucial energy engineering such as methane reforming, water gas shift reaction, and methanol synthesis due to the high specific surface area, excellent thermal conductivity, and complex overlapping channels. However, the current understanding of the wake flow patterns and turbulent characteristics under superimposed perturbations caused by complex terminal protrusions of the accumulation structure is still unclear. This study utilized a PIV system with high spatial resolution and accuracy to conduct non-contact visual measurements of the wake velocity field. The complex turbulent data of the wake flow was analyzed using the POD method to extract the primary modal flow characteristics and the energy distribution of each mode. The analysis of the flow characteristic quantities reconstructed from different order range modes revealed that as the Reynolds number increased: the size of vortices formed by the protruded structure at the trailing end increased, while the scale of vortices formed by the sub-protruded structure decreased; furthermore, the energy distribution of the first and second modes decreased, indicating a decrease in the stability of the main flow pattern; the impact pattern for the similarity between the reconstructed flow field and the transient flow field showed significant changes depending on the number of included modes.