高温氧化对超高温陶瓷材料耦合传热的影响

超高温陶瓷材料暴露于极端高温飞行环境中会导致其发生氧化,表面生成的氧化物具有不同的热物性从而对传热过程造成影响。针对预氧化的ZrB₂和ZrB₂-SiC,基于氧化模型预测氧化层(ZrO₂、B₂O₃、SiO₂和SiC耗尽层)厚度,利用有限元建立圆柱形代表性体积单元,并与外部高超声速流场的CFD (Computational Fluid Dynamics)求解器相耦合,研究了高温氧化对超高温陶瓷材料的耦合传热的影响。计算中采用分区求解方法,通过耦合界面处非匹配网格间的插值完成实时数据交换,实现了基于Navier-Stokes方程的流动求解器与有限元求解器的多场耦合计算。ZrB₂、ZrB₂-SiC以及氧化生成物的热物性均为温度相关,通过理论计算给出了B₂O₃挥发及SiC耗尽导致的多孔结构的有效热导率和有效比热容。瞬态耦合传热分析的结果表明:ZrB₂在预氧化后其热阻能力略有提高, ZrB₂-SiC氧化前后的热阻变化很小,并且在相同流动环境条件下,氧化后ZrB₂的热阻能力高于氧化后ZrB₂-SiC的热阻能力。 

Effects of oxidation on coupled heat transfer of ultra-high temperature ceramic materials at high temperature

Extreme high-temperature flight environment exposure of ultra-high temperature ceramic materials will result in their oxidations,and the generated oxide products on the surface which have different thermal-physical properties,thus will affect the heat transfer process.For pre-oxidized ZrB2 and ZrB2-SiC materials,the thickness of oxidation layer (ZrO2 ,B2 O3 ,SiO2 and SiC-depleted layer)was calculated from oxidation models.Cylindrical repre-sentative volume unit was modeled using finite element,and it was coupled with an external hypersonic flow CFD (Computational Fluid Dynamics)solver to study the effects of high-temperature oxidation on coupled heat transfer of ultra-high temperature ceramic materials.Multi-field coupling calculation was implemented in conj unction with flow solver of Navier-Stokes equation and the finite element solver by using partition algorithm,and real time data ex-change between non-matched meshes was achieved by interpolating data at coupling surface.All thermal-physical properties of ZrB2 ,ZrB2-SiC and oxidation products are temperature dependent.The effective thermal conductivity and effective heat capacity of porous medium,which are caused by the evaporation of B2 O3 and the depletion of SiC, were calculated based on theoretical calculation.The transient coupled heat transfer analysis results indicate that, the thermal resistance of ZrB2 after preoxidation is slightly higher than that of original ZrB2 ,and there is little varia-tion for thermal resistance of ZrB2-SiC materials before and after oxidation.Moreover,for the same flow environ-mental conditions,ZrB2 after oxidation has higher thermal resistance than ZrB2-SiC after oxidation.