Direct numerical simulation (DNS) of a turbulent boundary layer with moderate Reynolds number was
performed to scrutinize streamwise-coherence of hairpin packet motions. The Reynolds number based on the
momentum thickness (θin) and free-stream velocity (U∞) was varied in the range Reθ=1410~2540 which was
higher than the previous numerical simulations in the turbulent boundary layer. In order to include the groups
of hairpin packets existing in the outer layer, large computational domain was used (more than 50δo, where δo
is the boundary layer thickness at the inlet in the streamwise domain). Characteristics of packet motions were
investigated by using instantaneous flow fields, two-point correlation and conditional average flow fields in
xy-plane. The present results showed that a train of hairpin packet motions was propagating coherently along
the downstream and these structures induced the very large-scale motions in the turbulent boundary layer.