Time resolved stereo-PIV measurements of the horseshoe vortex system in a low aspect ratio pin-fin array

The horseshoe vortex system is a series of vortices which develop at the junction between an endwall and a bluff body during impinging flow. Pin-fin arrays are an internal cooling feature where bluff-bodies are arranged in an array to act as turbulators and increase heat transfer to a cooling fluid. The present study examines how the horseshoe vortex system evolves at pin-fins of different row positions in a low aspect ratio pin-fin array. Time-resolved stereo particle image velocimetry was employed in the stagnation plane of pin-fins in rows 1, 3, and 5 for a Reynolds number, based on pin-fin diameter, of 2.0e4. The shape of the time-mean horseshoe vortex profile was found to change from row 1 to row 3 due to upstream flow acceleration and buffeting by turbulence. The bimodal nature of the horseshoe vortex was established regardless of row number, and the oscillation between the backflow and zero-flow modes was shown to drive regions of maximum (formula presented) and (formula presented). (formula presented) was found to be dominated by upstream wake shedding instead of horseshoe vortex effects. Turbulent kinetic energy in the horseshoe vortex region was found to be amplified above mid-channel levels for each row. The shape of turbulent kinetic energy in this region was found to vary with row location due to the changing influences of (formula presented), (formula presented) and (formula presented). Finally, the backflow was discovered to have strong, negative values of (formula presented), while the region closer to the pin on the opposite side of the spiral node contained strong, positive values of (formula presented).