2014/02/24 by Ping Lu, Chaoqun Liu, Lu, Ping +1
Engineering · Environmental Science · #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Fluid Dynamics and Turbulent Flows #Fluid Dynamics and Vibration Analysis #Wind and Air Flow Studies
paper · pdf · doi:10.48550/arxiv.1402.5896
openalex publication_date 2014/02/24 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/01
The small vortex generation is a key issue of the mechanism for late flow transition and turbulence generation. It was widely accepted that small length vortices were generated by large vortex breakdown. According to our recent DNS, we find that the hairpin vortex structure is very stable and never breaks down to small pieces. On the other hand, we recognize that there are strong positive spikes besides the ring neck in the spanwise direction. The strongly positive spikes are caused by second sweeps which are generated by perfectly circular and perpendicularly standing vortex rings. The second sweep brings energy from the invisid region downdraft to the bottom of the boundary layers, which generates high shear layers around the positive spikes.Since the high shear layer is not stable, all small length scales (turbulence) are generated around high shear layers especially near the wall surface (bottom of boundary layers). This happens near the ring neck in the streamwise direction and besides the original vortex legs in the spanwise direction.The small length scales then rise up from the wall surface and travel to the upper boundary layer.