Experimental investigation of central blockages in a narrow rectangular channel using PIV: comparative study of square and diamond blockages

This study investigates the flow characteristics in a rectangular channel with center square and diamond blockages ( α =30%) at varying Reynolds numbers ( Re = 1268 – 4438) using particle image velocimetry (PIV). Time-averaged analysis, turbulence statistics, and proper orthogonal decomposition (POD) were employed to examine the effects of blockage geometry on vortex evolution and turbulent kinetic energy dissipation. Key findings demonstrate that the diamond blockage induces localized high-vorticity zones due to its sharp vertices, resulting in stronger vortex cores. In contrast, the square blockage triggers flow stagnation due to its right-angled geometry, exhibiting broader turbulent kinetic energy dissipation and imposing stronger disturbances on the wake fluid. POD analysis and flow field reconstruction confirm the periodic vortex shedding in both blockage conditions. The present results can provide effective experimental data for blockage accident simulations of plate-type fuel assemblies.