Flow mechanism across 180° sharp bend of matrix-cooled serpentine channel

Abstract

Vortex merging and evolution mechanisms have been characterized across the 180° sharp bend region of matrix-cooled serpentine channel with the help of stereo Particle Image Velocimetry (PIV) system. Complete evolution of flow phenomenon is captured through measurements in multiple vertical and horizontal planes, and the mechanism responsible for evolution of vortices at a typical Reynolds number (Re) of 6500 has been explored. It was observed that the matrix subchannel typically produces a kind of swirling pattern downstream of the matrix structure, which is similar to the swirling flow occurring in various other application areas. Two co-rotating vortices emanate out of matrix subchannels (observed in secondary plane), which immediately merge into a single vortex at the onset of the bend and propagate further downstream of the bend section, where a pair of side-by-side counter-rotating vortices are observed later. Numerical simulations have also been performed to get the pressure distribution and flow characteristics within oblique/inclined planes along the bend, which are difficult to obtain experimentally through PIV. Results demonstrate that the vortical structures lose their strength during merging and turning, significantly reducing turbulence while passing through the bend. Based on the combination of experimental and numerical observations, a conceptual diagram depicting flow dynamics has been proposed, which provides the overall perspective of vortices evolution and merging across the bend.