DNS of Turbulent Spot Developing Into Turbulent Stripe 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 this work, 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. We found that a spot developed into the turbulent stripes, as the spot split in the spanwise direction and took in the form of V-shape. Quasi-laminar and turbulent regions coexist inside the spot and each region became multiple V-shape. Several branching turbulent regions expanded from the edge of the spot and parallel to each other obliquely to the streamwise direction with an angle of about 30°. It was also found that the branching turbulent region gave rise to oblique waves at their edges.