Boundary-layer - free stream interactions in horizontal and sloping open-channels

This paper treats the open-channel flow problem as a boundary layer-free stream interaction problem, in analogy to viscous-inviscid interactions in gas dynamics. Convergent numerical results are obtained by an iterative solution procedure which alternately solves the boundary layer problem and the free stream equation. In a horizontal channel, the boundary layer is found to accelerate the external flow in the subcritical case. In the supercritical case the external flow is, on the other hand, retarded. A particularly strong interaction is observed for initial Froude numbers close to unity. In a downward sloping channel the interaction effects are found to oppose the effect of the sloping channel bed.