RANS-based analysis of flow state evolution and the secondary Nusselt number peak in round impinging jets

For single jet impingement, it is well established that a secondary peak emerges in the radial distribution of the Nusselt number on the impingement plane under appropriate combinations of nozzle-to-plate distance, Reynolds number, and other conditions. To acquire more information about the flow state evolution and the secondary peak, and to deepen the understanding of the flow and heat transfer characteristics of jet impingement, round jet impingement cases with R e = 23,000 and different nozzle-to-plate distances H / D are numerically simulated using the SSTLM model. The results in terms of the local characteristic length and velocity scales, the development and coupling of the inner and outer layers, the shape factor, the turbulence quantities, and other details of the flow and heat transfer fields are thoroughly analyzed to seek an approach for tracking the flow state changes using RANS results. Through quantitative and qualitative analyses, the effects of the interaction between the inner and outer layers on the flow transition, the intensity of relaminarization and other flow and heat transfer characteristics are discussed.