超音速平板边界层转捩中层流突变为湍流的机理研究

Study of the Mechanism of Breakdown in Laminar-Turbulent Transition of a Supersonic Boundary Layer on a Flat Plate

采用空间模式,对来流Mach数为4.5的平板边界层转捩过程做了直接数值模拟.对结果进行的分析发现,在层流_湍流转捩的突变(breakdown)过程中,层流剖面得以快速转变为湍流剖面的机理在于平均剖面的修正导致了其稳定性特征的显著变化.虽然在层流下第2模态T_S波更不稳定,但在层流突变为湍流的过程中,第1模态不稳定波也起了重要作用.

Spatial mode direct numerical simulation has been applied to the study of the mechanism of breakdown in laminar-turbulent transition of a supersonic boundary layer on a flat plate with Mach number 4.5. Analysis of the result showed that, during the breakdown process in laminar-turbulent transition, the mechanism causing the mean flow profile to evolve swiftly from laminar to turbulent was that the modification of mean flow profile by the disturbance, when they became larger, leads to remarkable change of its stability characteristics. Though the most unstable T-S wave was of second mode for laminar flow, the first mode waves played the key role in the breakdown process in laminarturbulent transition.