Anti-hairpin vortices in the buoyancy-driven turbulent boundary layer

TL;DR

This paper reveals that in buoyancy-driven turbulent boundary layers, hairpin vortices point upstream and are associated with high-speed streaks, challenging previous assumptions and enhancing understanding of buoyancy effects in turbulence.

Contribution

It uncovers the intrinsic upstream orientation of hairpin vortices and their association with high-speed streaks in buoyancy-driven turbulence, providing new insights into flow structures.

Findings

Hairpin vortices point upstream in buoyancy-driven turbulence.

Vortices straddle high-speed streaks instead of low-speed streaks.

Reynolds shear stress quadrants are dominated by the first and third quadrants.

Abstract

Here we show the hairpin vortices point the upstream direction of flow instead of downstream, and this characteristic is found intrinsic behavior for turbulent buoyancy-driven boundary layer. We uncover the coherent vortices straddle high-speed streak instead of low-speed streak; moreover, the quadrant of the tangential Reynolds shear stresses dominates the first and third quadrant instead of the second and fourth one. These findings may help to improve our understanding of buoyancy-driven flow and buoyancy effects in turbulent models.