Wall pressure and secondary-flow origination in a square duct

The secondary flow of Prandtl's second kind is a typical feature of turbulent flow in a duct with a noncircular cross section. In this paper, we proposed a physical mechanism on the formation of the secondary flow by analyzing the momentum balance along selected paths. The blocking effects of intersecting walls cause the pressure at the corner to be higher than that at the wall midpoint. Driven by the pressure gradient, fluids above the wall flow away from the corner, complemented by an inflow toward the corner along the diagonal. The proposed mechanism is confirmed using data from direct numerical simulation with the friction Reynolds number Re-tau up to 900. Published under license by AIP Publishing.