考虑化学非平衡效应的高温湍流边界层统计特性分析

Statistical characteristics of high-temperature turbulent boundary layer considering chemical non-equilibrium effect

新型高超声速飞行器在中低空以极高马赫数飞行时,会面临湍流与高温化学非平衡效应耦合作用的复杂流动环境,但相关研究工作还比较少。以楔形体头部斜激波后的高温非平衡湍流边界层作为研究对象,分别采用两种气体模型(完全气体模型和空气化学反应模型)开展直接数值模拟研究,对比分析了Walz关系式、强雷诺比拟关系(Strong Reynolds Analogy,SRA)、湍动能生成耗散机制和湍流可压缩效应。计算结果表明,弱可压缩假设在高温化学非平衡湍流边界层中仍然成立。采用无量纲恢复焓建立的与速度之间的关系式,可以消除马赫数、化学反应等因素的影响,与直接数值模拟的结果符合较好。GHSRA(Generalized Huang’s SRA)可以较好地描述温度脉动与速度脉动之间的强雷诺比拟关系。且采用半当地尺度归一化时,不同工况下湍动能输运方程各项的分布能够较好地符合。化学非平衡效应及高马赫数效应引起的可压缩效应有限。

When flying at extremely high Mach numbers at low and medium altitudes,the new hypersonic vehicles will encounter a complicated flow environment,i.e.the coupling between turbulence and chemical nonequilibrium.However,there are only very few related studies so far.In this work,direct numerical simulations(DNS)were performed for the high-temperature and non-equilibrium turbulent boundary layer after the leading shock of a cone using two different gas models,i.e.the calorically perfect gas model and the chemical nonequilibrium gas model.The Walz equation,the strong Reynolds analogy(SRA)relation,the turbulent kinetic energy production-dissipation mechanism and the compressibility effects were compared and analyzed.The results show that the weak compressibility hypothesis still holds in the chemical non-equilibrium turbulent boundary layer.When using the relation between the non-dimensional recovery enthalpy and the velocity,effects of the Mach number,the chemical reaction,etc.can be eliminated,and the prediction agrees well with the DNS result.GHSRA(Generalized Huang’s SRA)is appropriate to describe the relation between the temperature fluctuation and the velocity fluctuation.The‘semi-local’scaling can collapse the distribution profiles of the turbulent kinetic energy budgets under different flow conditions.The compressibility effect caused by the chemical non-equilibrium and the high Mach number is limited.