Study on thermal protection characteristics of non-enclosed thermal cloak

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The aerodynamic heat of hypersonic vehicle nose cone can reach MWm<sup>-2</sup> magnitude during flight, which could be transferred to the interior of hypersonic vehicle in the form of conduction and radiation. High efficient thermal insulation material is significant to keep internal electronic components working safely. Thermal metamaterials can regulate the macroscopic heat flow path, which have been developing rapidly and have a wide application prospect in the field of thermal protection. In this paper, a non-enclosed theoretical thermal cloak is designed to guide heat flow around hypersonic vehicle nose cone by using the transformation multithermotics, which can control thermal conduction and radiation simultaneously. A multi-layer structure is designed as cloak's simplified approximation due to the anisotropic parameters. Based on the software COMSOL, the thermal protection characteristics and heat transfer mechanism of the cloak and multi-layer structure are studied numerically. The results show that heat can flow around the object in the form of conduction and radiation in both theoretical thermal cloak and multi-layer structure, so the heat transferred to the inner area is decreased. Compared with the thermal insulation material, the heating rate of the protected area slows down, and the temperature at the front of the hypersonic vehicle nose cone is significantly reduced. However, the improvement of the thermal protection performance of cloak and multi-layer structures requires that the solid and radiative thermal conductivities of the material be lower than those of the original thermal insulation materials. To solve this problem, a non-enclosed theoretical extrapolation thermal cloak is further proposed. The solid and radiative thermal conductivities of extrapolation thermal cloak are non-singular, which could be higher than those of the original thermal insulation materials. Numerical simulation results show that the extrapolation thermal cloak can guide heat flow around object, so the thermal protection capability is improved significantly. Compared with the thermal insulation materials, the temperature of the front of the hypersonic vehicle nose cone is reduced by 100 K, and the temperature of the inner central zone of the hypersonic vehicle nose cone is reduced by 10 K. The non-enclosed extrapolation thermal cloak provides a new approach for thermal protection and is suitable for complex target areas, showing great application potential in thermal protection.