Open-channel flow, a branch of hydraulics and fluid mechanics, is a type of liquid flow within a conduit with a free surface, known as a channel. The other type of flow within a conduit is pipe flow. These two types of flow are similar in many ways, but differ in one important respect: the free surface. Open-channel flow has a free surface, whereas pipe flow does not.
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Classifications of flow
Open-channel flow can be classified and described in various ways based on the change in flow depth with respect to time and space. The fundamental types of flow dealt with in open-channel hydraulics are:
Time as the criterion Space as the criterionSummary of the classification of open-channel flow
Steady flow Uniform flow Varied flow Gradually varied flow Rapidly varied flow Unsteady flow Unsteady uniform flow (rare) Unsteady flow (“unsteady varied flow” should be here, but it is a practically impossible condition, so it is known simply as unsteady flow) Gradually varied unsteady flow Rapidly varied unsteady flowStates of flow
The behavior of open channel flow is governed by the effects of viscosity and gravity relative to the inertial forces of the flow. Surface tension has a minor contribution, but does not play a significant enough role in most circumstances to be a governing factor. Depending on the effect of viscosity relative to inertia, as represented by the Reynolds number, the flow can be either laminar, turbulent, or transitional.