A numerical study of a vortex ring impacting a permeable wall

In this paper, we numerically simulate a vortex ring impacting a permeable wall by using a lattice Boltzmann method. The study is motivated by recent publications on vortex ring/permeable wall interaction and our desire to address some of the unanswered questions such as evolution of core vorticity, kinetic energy, and enstrophy of the flow field during the interaction. The simulation was conducted for a wide range of parameters, namely, wall open-area ratios (phi) (0 <= phi <= 1), wire structure dimensions (A) (0.015 <= A <= 0.1), wall-thicknesses (H) (0.015 <= H <= 1), and Reynolds numbers (R-e Gamma) (500 <= R-e Gamma <= 5000). Results show that the flow characteristics upstream and downstream of the permeable wall depends on these parameters. Specifically, increasing phi or R-e Gamma enhances vorticity transport across the permeable wall, leading to a regenerated vortex ring, while increasing H impedes vorticity transportation and the formation of regenerated vortex ring. Moreover, larger A promotes vortex shedding from wire grids and generates fine-scale flow structures in the wake region. The study further shows a strong correlation between the attainment of maximum enstrophy and the lifting of the secondary vortex ring from the wall by the induced velocity of the primary vortex ring. While increasing phi causes the peak enstrophy to decrease in the upstream region and increase in the downstream region, increasing wall thickness has the opposite effect on the peak enstrophy. On the other hand, increasing wire dimension reduces peak enstrophy in both the upstream and downstream regions, while increasing Reynolds number has the opposite effect on the peak enstrophy. (C) 2014 AIP Publishing LLC.