AdvancedTopic 74 of 105Thermodynamics & Fluids
Open channel flow
Flow with free surface, described by Manning's equation.
In depth
Free-surface flows driven by gravity: Manning V=(1/n)R^{2/3}S^{1/2}. Froude number Fr=V/√(gy) separates subcritical (Fr<1), critical and supercritical flow. Specific energy and normal depth are central design ideas for channels and spillways.
Key points
- Hydraulic radius R=A/P
- Channel roughness n
- Weirs and flumes measure flow
ExampleA concrete channel with n=0.013 and slope 0.001 carries a few m³/s per m² of section.
Open channel flow describes rivers, canals and sewers, where the free surface changes with flow and slope, so it governs flood and drainage design.
What is Open channel flow?
Flow with free surface, described by Manning's equation.
Why is it important to understand open channel flow?
Open channel flow describes rivers, canals and sewers, where the free surface changes with flow and slope, so it governs flood and drainage design.
What is Manning's equation used for?
It estimates the velocity and flow in open channels from the slope, roughness and cross-section geometry.
What does the roughness coefficient describe?
The resistance of the channel surface to flow, which is higher for rough, vegetated or irregular channels.
How is Open channel flow used in practice?
Typical applications include sizing a drainage channel to carry a design storm flow, estimating the depth of flow in a canal with a given slope and designing a culvert under a road to avoid flooding.
What should I learn before Open channel flow?
Study "Airfoil aerodynamics" first (topic 73 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Open channel flow?
Hydraulic radius R=A/P. Channel roughness n. Weirs and flumes measure flow.
Can you give an example of Open channel flow?
A concrete channel with n=0.013 and slope 0.001 carries a few m³/s per m² of section.
What comes after Open channel flow?
The next topic is "Hydraulic jump", which builds directly on this one.
How difficult is Open channel flow?
It is classed as Advanced in Thermodynamics & Fluids (topic 74 of 105). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Thermodynamics & Fluids.