2 - Fundamentals of open channel flows

Abstract

This chapter discusses the fundamentals of open channel flows. Open channel flow describes the fluid motion in open channel. The free surface is at constant atmospheric pressure. The driving force of the fluid motion is a combination of pressure (e.g. beneath a sluice gate) and gravity (e.g. sloping channel). In an open channel, the pressure distribution is always hydrostatic, unless the curvature of the streamlines is important. Furthermore, in fluid mechanics and hydraulics, the basic principles are the equations of continuity or conservation of mass, of momentum or conservation of momentum and conservation of energy. Another equation is the Bernoulli equation which is derived from the differential form of the momentum principle. In this chapter, the simplest form of the fundamental principles is developed: i.e. for steady one-dimensional flows. In addition, the hydraulics of short transitions is developed in the chapter, including the concept of specific energy, critical flow conditions, and the hydraulic jump. For the frictionless flow in a horizontal channel, the Bernoulli principle implies that the specific energy is constant along the channel. Considering a short, smooth transition in a non-horizontal channel, the upstream and downstream total heads are equal, by application of the Bernoulli equation.