Coupled convective-radiative heat transfer enhancement in high-temperature hydrogen combustion using oscillating jet

Thermal protection in hydrogen combustion environments is governed by, and therefore highly sensitive to, the coupled effects of convective cooling and radiative heat transfer. The aim of this study was to investigate oscillatory jet film cooling under high-temperature hydrogen combustion conditions, with particular attention to the role of radiation, an effect often omitted in conventional cooling analyses. Unlike our prior convective-only analysis of this configuration, this study couples its transient aerodynamic behavior with a participating-media radiation model under realistic hydrogen-combustion products. The radiative conditions were investigated using the Discrete Ordinates (DO) radiation model, with the two main variables being surface emissivity and water vapor concentration in the cooling air. The thermal behavior was studied with respect to wall emissivity, and the effect of introducing water vapor into the cooling air was incorporated into the model. The results showed that neglecting radiation leads to underestimated wall temperatures and overestimated cooling-film thickness, a meaningful discrepancy in practical design terms. When radiation was included, predicted wall temperatures rose from 1300K to 1600K as the minimum value, and the cooling film became noticeably thinner. Increasing wall emissivity from 0.6 to 0.8 reduced surface temperature by only 20–40 K, suggesting limited sensitivity to emissivity in this range. Adding water vapor to the cooling air showed similarly modest benefits. This research underscores the need to account for radiative effects in cooling evaluations of components in advanced hydrogen-powered energy systems operating at high temperatures.