11. Free surface flows

Consider a liquid (water) flowing through a channel whose length is long compared to the cross-sectional dimensions of the prismatic cross-section, and whose walls are of the same type along its length. The pressure is uniform over the free surface (atmospheric pressure). Flow can be varied in the direction of flow and is assumed to be always turbulent. In a real flow, the walls are not flat, and their irregularities on a large scale induce weak secondary currents superimposed on the main flow, which will be the outflow of the unidirectional motion taken into account. As a first approximation, we'll assume that velocity is uniform in a given section and equal to the flow velocity: figure 32 shows the velocity distribution...