Breakdown过程长度及其前后边界层名义厚度的变化

采用数值模拟的方法,模拟了平板边界层的转捩过程及发展的湍流,在此基础上,研究了不同初始扰动对转捩持续时间和湍流边界层厚度影响的共性和差异.研究结果表明:在不同的波数情况下,计算得到不同的初始扰动引起的转捩的持续时间不同.在给定基本波数情况下,如果初始扰动在展向不是对称的,那么,它们引起的转捩后平均边界层厚度与转捩起始点处边界层厚度的比值δ_e/δ_b在相当长的时间内表现出相同的增长规律,这一增长规律与所加的初始扰动无关.然而,展向是非对称的表现出不同增长规律. 

Durations of transition and variation of boundary-layer thickness before and after breakdown

Temporal mode direction numerical simulation has been done for the breakdown process of laminar-turbulent transition and the fully developed turbulence in an incompressible boundary layer on a flat plate.Based on the computational results,the common and different characteristics of the durations of transition and the time-averaged boundary-layer thickness induced by different initial disturbances were discussed.Analytical results show that under different basic wave numbers,the durations of transition induced by different initial disturbances are different to one another.On the other hand,under given basic wave numbers,if the initial disturbances are dissymmetrical in span-wise direction,the ratio of the time-averaged boundary-layer thickness after transition to the boundarylayer thickness at the beginning of the breakdown process in the transition,δ_e/δ_b,shows the same growth rate with respect to time,which is independent of the initial disturbances.In contrast,initial symmetric disturbances will induce different growth trends.