Heat transfer mechanisms in impinging jets: The role of vortex dynamics

This study employs direct numerical simulation (DNS) to investigate the interplay between coherent flow structures and wall heat transfer in a round impinging jet configuration with random perturbations at the inlet. The dimensionless nozzle-to-plate distance ( H / D = 2 . 0 ) and Prandtl number ( P r = 0 . 7 ) are fixed, while the Reynolds number ( R e ) varies between 2500 and 6000. The radial distribution of the heat transfer coefficient reveals multiple peaks for R e ≥ 2500 . For the secondary maximum, visualization using the Q-criterion identifies nearly axisymmetric paired vortex rings close to the wall. Detailed analysis shows that the evolution of these vortical structures is directly linked to variations in shear stress and the Nusselt number . The unsteady separation-reattachment mechanism, driven by the interaction between vortex pairs and the wall, significantly enhances heat transfer in this region. At higher R e , a third peak is observed, driven by a re-pairing phenomenon of separated vortex pairs. This process causes the vortex pairs to return to the wall, resulting in non-axisymmetric intensification of the local heat transfer coefficient . These findings deepen the understanding of how coherent structures govern heat transfer in impinging jets, providing insights that could guide the design of optimized industrial systems. • Unsteady separation periodically interacts with the wall, forming the 2nd heat transfer peak. • Vortex re-pairing intermittently interacts with the wall, forming the 3rd heat transfer peak. • Characteristic frequency in free jet distinguishes transition to the turbulent state.