考虑气体扩散渗透的隔热材料瞬态隔热性能数值模拟

高超声速飞行器机动飞行时环境压力变化导致隔热材料沿厚度方向存在压力梯度,进而引起隔
热材料内气体的扩散渗透,影响隔热材料隔热性能。为研究气体扩散渗透对隔热材料隔热性能的影响,建立了
隔热材料内气体扩散渗透模型,采用罗斯兰德近似、有限体积法建立了隔热材料内扩散渗透及辐射导热传热计
算模型,对气体扩散渗透条件下的瞬态隔热性能进行了数值模拟。算例模拟结果表明:对2 cm 厚纳米隔热材
料,在外界气压为0. 1 MPa,绝热面为真空的状况下,当渗透率大于10-14 m2 时,气体扩散渗透开始影响隔热材
料内传热,导致隔热性能降低,气体黏性系数对气体扩散渗透有显著影响,随着黏性系数降低,气体扩散渗流现
象显著;衰减系数对绝热面温度响应有显著影响,随着衰减系数增大,绝热面温度响应显著降低。

Numerical Simulation on Transient Insulating Properties ofThermal Insulation Materials With Gas Permeation

Pressure gradient in the insulation materials along the thickness direction, which results from the changes
in pressure around the maneuvering hypersonic vehicles, will lead to gas diffusion and permeation in thermal insulation
materials and affect the insulating property. In order to study the influences of gas diffusion and permeation on materials
insulating properties, a heat transfer model combined conduction radiation with gas diffusion and permeation was
established under Rosseland approximation for radiation heat transfer. The established control equations were solved by
finite volume method and the transient insulting properties under the condition of gas diffusion and permeation were numerically
studied. Results show that gas permeation begins to influence the heat transfer process and worsen transient insulating
property for a 2 cm nanometer insulation material when its permeability is greater than 10-14 m2 under the condition
where the heated surface is at environment pressure of 0.1 MPa and the unheated surface is in vacuum. Gas viscosity
has a significant influence on gas diffusion and permeation process and the diffusion process enhances with the decrease
in viscosity. Extinction coefficient has more significant influence on the thermal response at the insulated surface
than gas diffusion parameters and the temperature response decreases with the increase of extinction coefficient.