平板和翼型壁面上振荡流底边界层中拟序涡结构运动演化的大涡模拟研究

Large Eddy Simulation Study for Evolution of CoherentVortex Structure in Oscillatory Boundary Layer Flow over Flat-Plate or Winger-Type Wall

本文结合飞行器和船舶减阻机理的研究 ,利用大涡模拟的方法 ,建立了模拟振荡流边界层湍流运动特性的数学模型 ,进而对飞行器和船舶设计中遇到的 ,较为典型的两种边界层流动中拟序涡的生成过程进行模拟研究 ,计算结果表明 ,在振荡流加速阶段 ,靠近壁面处的流动由于剪切层的不稳定性而产生紊动 ,但受到主流的抑制不能得到充分发展 ;振荡流随着减速阶段的开始 ,紊动逐步变得更加强烈 ,并形成拟序涡结构。本文工作为进一步研究如何控制或适应边界层中湍流结构 。

Combined with the subject of drag reducing mechanism of aerocraft and ship, using the large eddy simulation method, a mathematical model has been set up for investigating the turbulence characteristics in oscillatory flow boundary layer. Moreover, the creating processes of coherent vortexes in two typical boundary layer flows have been simulated; one is boundary layer flow over flat - plate wall and the other is over winger-type wall, which are often encountered in designing aerocraft and ship. The calculation results show that the weak turbulence is triggered by the shear instability at the later stage of the acceleration period in oscillatory flow near wall, but it is suppressed by the main flow and cannot fully develop. With the beginning of the oscillatory flow deceleration, the turbulence gradually becomes much more intensive and forms coherent vortex structure. This research work establishes the reliable foundation for studying how to control or suit the turbulence structure in boundary layer and attain effect of drag reducing.