非封闭式热斗篷热防护特性

Thermal protection characteristics of non-enclosed thermal cloak

高超声速飞行器在飞行过程中产生大量气动热,高效的热防护技术对保证其正常工作具有重要意义.本文基于热超材料调控热流传播路径思想,针对高超声速飞行器头锥,采用坐标变换法设计非封闭式点变换热斗篷及简化近似的多层结构.COMSOL数值模拟研究表明,两种结构均有效实现导热和辐射热流的热绕流,使部分热量沿头锥表面传播,头锥前端温度显著降低,机体升温速率减缓.但其热防护性能的提升要求材料固相和辐射热导率低于原隔热材料.进一步设计了非封闭式域变换热斗篷,材料固相和辐射热导率均可高于原隔热材料.模拟结果表明,热绕流显著提升了域变换热斗篷的热防护能力,相比于纯隔热材料,头锥前端温度降低达100 K,机体降温达10 K,展现出重要的热防护应用潜力.

The aerodynamic heat of hypersonic vehicle nose cone can reach tens of MW/m^(2) during flight,which could be transferred to the interior of hypersonic vehicle in the form of conduction and radiation.High efficient thermal insulation technology is of significance in keeping internal electronic components working safely.Thermal metamaterials can regulate the macroscopic heat flow path,and they are developing rapidly and have a wide application prospect in the field of thermal protection.In this work,a non-enclosed point transformation 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 point transformation 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 point transformation thermal cloak and multi-layer structure,so the heat transferred to the inner area decreases.Comparing with the thermal insulation material,the heating rate of the protected area slows down,and the temperature in the front of the hypersonic vehicle nose cone is significantly reduced.However,the improvement of the thermal protection performance of point transformation cloak and multi-layer structures requires that the solid thermal conductivity and radiative thermal conductivity of the material are lower than those of the original thermal insulation material.To solve this problem,a nonenclosed region transformation thermal cloak is further proposed.The solid thermal conductivity and radiative thermal conductivity of region transformation thermal cloak are non-singular,which could be higher than those of the original thermal insulation material.Numerical simulation results show that the region transformation thermal cloak can guide heat flow around object,so the thermal protection capability is improved significantly.Comparing 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 region transformation thermal cloak provides a new approach to realizing thermal protection and is suitable for complex target areas,showing great application potential in thermal protection.