Fluid Mechanics: Flow Types Classifications in open channel flow

Updated: Jul 2, 2020


Kariba Dam (Zimbabwe)

Quick Introduction to Fluid Mechanics


Fluid mechanics is the branch of physics concerned with the mechanics of fluids (liquids, gases, and plasmas) and the forces on them.

As civil engineers, we use fluid mechanics analysis in two types of flows:


  1. Open channel flow

  2. Pipe flows


The main difference open channel flow and pipe flows is the boundary conditions and the free surface of the liquid.


1. Open Channel flow:


  • Open channel flows are characterised by a free surface (usually) open to the atmosphere.

  • Open channel flows examples are streams, rivers, artificial canals, irrigation ditches, flumes, pipe-lines, culverts, tunnels, sewer lines, gutters, domestic draining boards.


2. Pipe or duct flow:


  • All of the cross-section is taken up with the fluid. This is referred to as a "closed conduit".

  • The energy in pipe flow is expressed as head and is defined by the Bernoulli equation.

Classification of flow types


1. Steady and Unsteady flow


Flow is termed steady or unsteady according to whether the velocity and hence the depth at a particular point on the channel - varies with time (=temporal variations)