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

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.