Understanding flow and velocity

Before modeling water supply networks, you must have a basic understanding of the terminology used when discussing water flow and velocity.

• Pressure Flow — a unit of volume moving past a certain point within a unit of time. Flow is measured in different units, depending upon its application.
• Velocity — the distance of a given fluid within a unit of time, or how fast a fluid is moving.
• Flow — equivalent to the velocity of the water multiplied by the radius of the pipe squared. The smaller the pipe, the greater the velocity at the same flowrate.
• Low velocities can result in sediment deposits, while changes in velocity can lift and release these deposits.
• Flow moving through smooth, unobstructed pipework will move at a constant velocity and is known as laminar flow.

• Headloss — the combination of energy losses within a pipe, such as frictional contact with the pipe wall or bends in the pipe.

• Turbulent flow — flow that is disrupted by bends or roughness of a pipe wall.
• Losses — increase velocities and flowrates, requiring more energy to overcome. Losses are usually measured per distance. In WS Pro, the Darcy-Weisbach equation is used to calculate headloss.
• Hydraulic transient (a.k.a. surge, water hammer) — in water networks, refers to pressure changing with time and typically reflects rapid or unexpected changes in pressure.