Confinement effect on heat transfer and fluid dynamics of air jet impingement on a flat surface: A Numerical study

The confinement effect on local heat transfer and fluid dynamics of impinging air jets on a smooth flat surface was numerically studied for various Reynolds number ( Re = 16,000 - 48,000), jet-to-impinging surface spacings ( z/d = 0.5- 6) and confinement ratios ( L/d = 0 -15). The complexities of heat transfer and fluid dynamics were analyzed using the Nusselt number ( Nu ) and pressure coefficient ( C p ). Numerical validation of three turbulence models (viz., Transition SST, SST k-ω , Transition k-kl-ω ) showed strong alignment with the experimental data. Among these models, the Transition SST model resulted in higher accuracy with experimental data. The result revealed that the influence of L/d on Nu was negligible in stagnation area and is highly significant in wall jet area when z/d was less than 1 for all Re values. This phenomenon arises from the impact of confinement on development and circulation of wall jet at lower z/d . In unconfined and confined jets, the pressure coefficient reached its highest value at stagnation point and subsequently diminished as the flow moved radially outward across the surface. The confined jets exhibited zones of sub atmospheric pressure, which became more pronounced as the L/d ratio increases and z/d ratio decreases, consistently for all Re values. This was due to acceleration and recirculation of flow within the confined space, resulting in localized pressure drops. The Nu correlations at stagnation point and wall jet area were obtained with maximum deviations of ±9% and ±5% respectively. The results demonstrate that confinement geometry has a pronounced impact on jet structure and heat transfer performance at lower jet to plate spacing .