Wake characteristics of a porous-coated wall-mounted cylinder using tomographic particle image velocimetry

The wake of finite wall-mounted cylinders exhibits strong three-dimensional features due to the combined influence of the free end and the base. Tomographic particle image velocimetry is used to investigate the wake of a wall-mounted cylinder coated with a 3-mm-thick, 40 pores per inch open-cell polyurethane foam layer with a nominal porosity of approximately 97% at a Reynolds number of 1280 and an aspect ratio of 4. Rather than weakening large-scale vortex structures as commonly reported for porous coatings, under the investigated condition, the porous-coated cylinder exhibits more organized and pronounced primary Kármán-type vortex shedding than the smooth cylinder baseline. This behavior is associated with systematic changes in the mean flow and turbulence statistics, including an elongated recirculation region, a downstream shift in turbulence production, and a reduced influence of three-dimensional end effects. Proper orthogonal decomposition provides further evidence for the more organized and pronounced primary Kármán-type vortex shedding, as indicated by reduced energy in modes associated with three-dimensional end effects and increased energy in the dominant Kármán-type shedding modes. This study provides new experimental insight into the three-dimensional wake dynamics of porous-coated wall-mounted cylinders.