Physics of multiple level hairpin vortex structure

Authors: YiQian Wang Hassan AlDujaly YongHua Yan Ning Zhao ChaoQun Liu

Publish Date: 2016/01/15

Volume: 59, Issue: 2, Pages: 624703-

PDF Link

Abstract

Previous experimental and numerical studies have revealed that the hairpin vortex is a basic flow element of transitional boundary layer The hairpin vortex is believed to have legs necks and a ring head Based on our DNS study the legs and the ring head are generated separately by different mechanisms The legs function like an engine to generate low speed zones by rotation create shear layers with surrounding high speed neighbor fluids and further cause vortex ring formation through shear layer instability In addition the ring head is Ωshaped and separated from quasistreamwise legs from the beginning Contrary to the classical concept of “vortex breakdown” we believe transition from laminar flow to turbulence is a “buildup” process of multiple level vortical structures The vortex rings of first level hairpins are mostly responsible for positive spikes which cause new vorticity rollup second level vortex leg formation and finally smaller second level vortex ring generation The third and lower level vortices are generated following the same mechanism In this paper the physical process from Λvortex to multilevel hairpin vortices is described in detail

Keywords: