Phase-Change Transpiration Cooling for Hypersonic Vehicles: A Comprehensive Review of Mechanisms, Modeling, Experiments, and Future Direction

Phase-change transpiration cooling, in which a liquid coolant flows through a porous medium, absorbs heat, and undergoes phase change while forming a protective gas film, is widely regarded as one of the most efficient active thermal protection concepts for next-generation hypersonic vehicles. This paper presents a comprehensive and critical review of the technology, tracing its evolution from early feasibility studies to recent flight demonstrations and systematically synthesizing advances in numerical modeling, experimental investigation, and engineering application. In modeling, existing approaches are classified into three categories: macroscopic two-phase mixture models, pore-scale interface-capturing methods, and mesoscopic direct numerical simulation and lattice Boltzmann methods. The mutual isolation of these three classes and the absence of a cross-scale coupling framework are identified as core methodological gaps. In experimentation, the review surveys mechanistic studies, ground-based qualification tests on complex structures, and the only two publicly reported flight validations, revealing a critical shortage of full-scale, long-duration, and multi-physics qualification data. Key physical phenomena, including vapor blockage, temperature oscillations, cooling hysteresis, and low-pressure freezing, are critically discussed. Beyond summarizing the state of the art, the review argues that the dominant research of small-scale, short-duration, single-physics studies fundamentally limits the generalizability of existing findings to real flight conditions. Six future research directions are proposed, emphasizing the need for a transition toward integrated, multi-physics, system-level demonstrations. This review is intended to serve as a reference for researchers and engineers working on hypersonic thermal protection, porous media heat transfer, and multiphase flow.