Pore-scale structure effect on phase-change heat transfer enhancement and drag reduction at the porous interface using CFD-PNM coupling method for transpiration cooling applications

Phase-change transpiration cooling holds great promise for thermal protection of high-speed vehicles. However, due to the lack of multiscale analysis, both the effect of pore-scale structures on heat transfer enhancement, and the coupling effect on drag reduction at the porous interface remain unclear. In this work, a multiscale fully coupled method between Computational Fluid Dynamics (CFD) and Pore-Network Model (PNM), termed as multiscale CFD-PNM coupling method, is employed. The effects of pore-scale structures, including porosity, pore body size and pore throat size, on the cooling efficiency and drag reduction performance are analyzed at both blowing region and post-blowing region. The transient blowing ratio, total coolant consumptions, and drag reduction effect are further quantified. The results show that, high porosity enhances both cooling efficiency and drag reduction along the channel but increases coolant usage. Larger pore throats improve post-blowing performance but may raise peak temperatures in the blowing region. Increasing pore body size yields limited cooling improvement, while amplifying coolant consumption and drag fluctuation. Based on the above conclusions, three designed porous structures considering graded distributions of both pore body and pore throat sizes have been proposed. Compared with porous structures with the same average porosity and pore throat size, the best designed porous structure performs an increase of ∼ 7.5 % for the cooling efficiency at the leading edge, with ∼ 49% less coolant consumption.