Thermal behavior of supercritical CO₂ inside scramjet cooling channels with different structural parameters

The supercritical CO₂ closed Brayton cycle is a promising cooling scheme for hypersonic aircraft. However, the high pressure and large heat flux make the thermal behavior of supercritical CO₂ inside the cooling channel extremely complex. In this study, the turbulent heat transfer of supercritical CO₂ in different structural cooling channels is simulated by using the modified turbulence model. A mathematical model of heat transfer coefficient is established by theoretical derivation. The model shows that the heat transfer coefficient is determined by 6 parameters such as turbulent viscosity (μ_tδ) and wall viscous shear stress (τ_w). The study found that there is still a slight local heat transfer deterioration (HTD) at low aspect ratio, even though the CO₂ is far from the critical state. By weight analysis of the mathematical model, the results show that the μ_tδ and the τ_w have the greatest influence on the heat transfer coefficient at the low aspect ratio, and their local decay causes the local HTD. With the change of aspect ratio, the bottom heat load and the μ_tδ have the opposite rule, which makes the cooling channel have an optimal aspect ratio and its value is about 0.8.