Flow mechanism governing finite wall effects in the classical vortex ring-wall interaction*

 Vortex ring-wall interaction applications appear in energy harvesting of vortices partially impinging on surfaces or interactions with close by structures. Canonically, when a vortex ring approaches an infinite surface, the induced flow along the surface forms a boundary layer that subsequently separates and rolls up into a secondary vortex structure. This phenomenon forces the primary vortex to rebound from the wall. When the finiteness of the wall is considered, the generation of secondary vorticity could be directly altered. To investigate this expectation, a programmable piston pump is used to drive a constant volume slug of fluid at various Reynolds numbers into a quiescent tank that contains interchangeable plates of various sizes. These plates are located more than 4 nozzle diameters downstream to allow full formation of the vortex ring without the influence of the plate. A control volume vorticity budget analysis is implemented that couples velocity field data from PIV and pressure gradient measurements from differential pressure transducers. Preliminary findings indicate that despite less space for vorticity growth, decreasing the plate size allows more vorticity to be ejected from the plate and roll up into the secondary vortex thereby increasing its strength. However, the effect on total secondary circulation generation through surface vorticity flux remains to be understood.