Abstract
We present the results obtained from direct numerical simulations of square-duct flow in a long streamwise computational domain at a range of Reynolds numbers 750≤Re_b≤1500, Re_b being based on mean bulk velocity and duct half width. Localized turbulence travelling downstream, equiliblium 'puff', is identified at the Reynolds number Re_b=850-1050. The mean secondary flow in 'puff' region is found to exhibit eight-vortex patterns observed in the secondary motion of Prandtl's second kind in turbulent square duct flow.
