Particle image velocimetry measurements of vortex rings head-on collision with a heated vertical plate

We report particle image velocimetry measurements of the collision of a vortex ring with a heated wall kept at constant temperature. We consider the case when both the vortex ring and the thermal boundary layer generated by the vertical heated wall are stable and laminar prior to any interaction. The impingement process can be divided into two parts. (i) A ring-driven stage, where the vortex ring grows in diameter while approaching the wall and therefore it sweeps progressively an increased surface on the wall. (ii) A boundary layer-driven stage, where the vortex ring moves upward due to the thermal convective motion generated by the heated wall. In some cases, the head-on collision triggers the ring's azimuthal instability as revealed by the formation of vortical structures arranged on a wavy starlike pattern and confirmed by flow visualizations. A single collision generates important velocity gradients and shear stresses along the wall accompanied with the creation of local vorticity normal to the vertical heated wall. Peak wall shear stresses occur near the point of impact of the vortex ring core. (C) 2010 American Institute of Physics. [doi:10.1063/1.3410800]