Hydraulic jump
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A hydraulic jump is a phenomenon from the science of hydraulics.
A hydraulic jump represents a wave that desires to move in upstream direction, but which it is unable to do, as the flow velocity of the water is larger than the wave's celerity (the speed of individual waves). A hydraulic jump can be recognised as a waterlevel that becomes larger in downstream direction. Tidal bores are a formed in this manner, and can be thought of as a moving hydraulic jump.
A hydraulic jump marks the border between supercritical and subcritical flow.
The wave celerity in shallow water is given by:
- <math>c = \sqrt{gd}\sqrt{\frac{\tanh{(kd)}}{kd}}<math> which is similar to <math> \sqrt{gd}<math> for small d;
In which:
- c = wave celerity (m/s)
- g = gravitational acceleration (9.81 m/s²)
- d = water depth (m)
- <math>k = \frac{2\pi}{\lambda}<math> wave number
Hydraulic_jump_in_sink.jpg
A daily example of a hydraulic jump can be seen when brushing your teeth: in the sink. Around the place where the tap water hits the sink, you will see a smooth looking flow pattern. A little further away, you will see a sudden 'jump' in the water level. This too, is a hydraulic jump.
See also: turbulence, laminar flow