Flow and Heat Transfer Characteristics of Compressible Impinging Jets at Low to Moderate Reynolds Numbers

Large eddy simulation (LES) is used to study the flow and heat transfer characteristics of compressible impinging jets with a Mach number (Ma) of 0.784, an impact height (H/D) of 5, and a Reynolds number (Re) ranging from 3300 to 8000. The average velocity and temperature, as well as the evolution process of vortices, are obtained. It is revealed that the heat transfer increases with the increase in Re. At a Re of 8000, the primary vortices break into small-scale vortices in advance, with no merged vortices found in the simulation results. In addition, dynamic mode decomposition (DMD) is performed for the temperature and pressure of the impinging jets, particularly focusing on the coherent structure at the spanwise location and on the impact plate. The results show that at a frequency St of 0.56, the coherent structures identified by DMD modes are large-scale symmetric structures. At frequency St of 1.04, these symmetric structures move downstream and gradually differentiate into small-scale structures. This indicates that the large-scale primary vortex forms a smaller scale secondary vortex upon impacting.