尖锐后缘尾流中的反向发卡涡

The unsteady organization and the evolution of the
coherent structures within the immediate wake of the sharp
symmetric trai领-edge of a NACA0012 airfoil is investigated
using two-component (2C) and tomographic particle image
velocimetry (Tomo-PIV). The inspection of the Tomo-PIV
results showed new vortical structures, introduced here as
counter-hairpin vortices, evolve in the wake region to direct
the turbulent mechanism towards recovery of the wake deficit.
These vortical structures are topologically similar to the
hairpins of a turbulent boundary layer as they appear to be Ushaped
but with inverted orientation. The spanwise portion of
a counter-hairpin vortex is in the vicinity of the wake
centerline and the legs are inclined at an approximately 60
degree to the wake axis in the downstream direction. They
partially wrap around the high speed streaks and frequently
sweep the high-speed flow towards the wake centerline. A
pattern recognition algorithm is applied to establish
characterization based on an ensemble averaged counterhairpin
vortex. The formation mechanism of the counterhairpin
vortices is attributed to the shear layer produced along
the wake centerline by the neioring of a low and a high
speed streak which promotes formation of spanwise vortices
that form the vortex by connection to quasistreamwise
vortices. 德国LaVision PIV/PLIF粒子成像测速场仪 体视层析粒子成像测速系统(Tomo-PIV)