多孔壁面对高速边界层最优增长条带二次失稳的影响规律

Effects of porous wall on secondary instability of optimal growth streaks in high speed boundary layers

边界层转捩是高超声速飞行器设计中的关键基础理论问题。当环境扰动强度较高时,将在模态扰动失稳区上游发生由最优增长条带二次失稳触发的亚临界转捩。为评估多孔壁面在亚临界转捩中的控制效果,以超/高超声速平板边界层流动为研究对象,建立了基于伴随抛物化稳定性方程的优化系统与求解方法。以最优扰动非线性演化形成的三维条带边界层为新的基本流动开展全局稳定性分析,研究表明:多孔壁面对第一模态频率范围内的二次失稳扰动为促进作用,对第二模态频率范围内的二次失稳扰动起抑制作用,并且转折频率接近局部快/慢模态的同步频率,对于工程应用中多孔涂层的布置方案具有一定的指导意义。

Boundary layer transition is a key fundamental theoretical problem in the design of hypersonic vehicles.High intensity environmental disturbances leads to subcritical transition upstream of the mode instability region,trig⁃gered by secondary instability of optimal growth streaks.To assess the effect of the porous wall on the subcritical tran⁃sition,this paper studies both super/hypersonic flat-plate boundary layer flows.Based on the adjoint parabolized stabil⁃ity equations,an optimization system as well as a numerical method is developed.The three-dimensional boundary layer flow with streaks resulted from the optimal disturbances of nonlinear evolution is used as the new base flow for the bi-global stability analysis.The result shows that,the secondary instability modes in the frequency range of the second modes are stabilized by the porous wall,while those in the frequency range of the first modes are destabilized,with the turning frequency close to the local synchronization frequency.Such regularity is helpful for the arrangement of porous coating in engineering applications.