Development of a turbulent spot into a stripe pattern in plane poiseuille flow

A structure consisting of quasi-laminar and turbulent regions in a stripe pattern, which can be found in a transitional plane channel flow, is called 'turbulent stripe'. In the previous works, the emergence of this structure was confirmed only in the case of decreasing Reynolds number from turbulent regime. In the present study, its formation from a turbulent spot has been investigated using a direct numerical simulation in a relatively large-scale computational domain of L_x × L_y × L_z = 731.4δ × 2δ × 365.7δ at Re_τ = 56 and L_x × L_y × L_z = 640δ × 2δ × 320δ at Re_τ = 64. We observed the stripe pattern of quasi-laminar and turbulent regions inside of the spot. However, the turbulent eddies decayed more rapidly for Re_τ = 56 than those for Re_τ = 64. The developed spot at Re_τ = 64 was found to be different form from that at Re_τ = 56.