Fundamentals and recent progress of additive manufacturing-assisted porous materials on transpiration cooling

The requirements for new generation vehicles in terms of the flight speed, thrust-weight ratio, and maneuverability necessitate the development of high performance and reliable propulsion systems where active thermal protection technology plays a crucial role. Transpiration cooling based on a microporous structure is considered as one of the most promising techniques for protecting the high heat flux walls from ablation in aerospace applications. Unlike conventional fabrication methods, additive manufacturing (AM) has been applied to fabricate three- dimensional (3D) porous structures with customized geometries that are specific to applications, i.e., in terms of the design of features such as the pore diameter, pore density, porosity, and pore morphology. Three major AM technologies (selective laser melting, inkjet, and stereolithography) followed by a post-printing process have been proposed for the additive manufacture of porous structures. In particular, 3D-printed porous structures have great promise for transpiration cooling applications. In this review, we discuss the detailed steps of porous structure topology design and a general framework is presented for AM. The heat transfer and strength performance are also provided for porous parts fabricated by AM. Furthermore, the applications of 3D-printed porous media in transpiration cooling with different regimes are described. This review concludes by explaining the current challenges and prospects for the next generation of 3D-printed porous structures in transpiration cooling systems.