Armfield C4-MKII, Инструкция по эксплуатации

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58
Theory
When water flowing rapidly changes to slower tranquil flow a hydraulic jump or standing
wave is produced. This phenomenon can be seen where water shooting under a sluice
gate mixes with deeper water downstream. It occurs when a depth less than critical
changes to a depth which is greater than critical and must be accompanied by a loss of
energy.
An undular jump occurs when the change in depth is small. The surface of the water
undulates in a series of oscillations which gradually decay to a region of smooth tranquil
flow
A direct jump occurs when the change in depth is great. The large amount of energy loss
results in a zone of extremely turbulent water before it settles to smooth tranquil flow.
By considering the forces acting within the fluid on either side of a hydraulic jump of unit
width it can be shown that:








+ − + = ∆
g 2
V
y
g 2
V
y H
2
b
b
2
a
a
where:
∆ H
= Total head loss across jump (energy dissipated) (m)
V
a
= Mean velocity before hydraulic jump (m s
-1
)
y
a
= Depth of flow before hydraulic jump (m)
V
b
= Mean velocity after hydraulic jump (m s
-1
)
y
b
= Depth of flow after hydraulic jump (m)
Because the working section is short y
a
≈ y
1
and y
b
≈ y
3
Therefore simplifying the above equation:
( )
3 1
3
1 3
y y 4
y y
∆ H
−
=