Turbulent Energy Production Mechanism in General Boundary Layer Transition

Summary

Most of the laminar boundary layers encountered in industrial use experience rather high turbulence intensity oncoming flow, or are largely modified into three-dimensional(3D) structure by external forces, and transition process becomes different from that of two-dimensional boundary layer(2D) with low turbulence intensity back ground. Such transition processes have been called as “Bypass transition”, and “3D boundary layer transition”.

Present investigation is focused on the clarification of the complicated transition mechanism in such general boundary layers. Through systematic investigation using several different kinds of experimental models, it became to clear that streamwise vortex as the primary instability, and then local inflectional instability as the secondary instability start to appear. Therefore, it can be said that the consistent transition mechanism which is important not only in academic interest, but also in industrial application is the generation of streamwise vortex (steady) as the primary instability, and then locally appeared wave(unsteady) instability as the secondary inflectional instability. Appearance of this secondary instability can be said as the key event for the turbulent energy production in general.