Hydraulic jump

When this happens, the jump can be accompanied by violent turbulence, eddying, air entrainment, and surface undulations, or waves.

However, the mechanisms behind them are similar because they are simply variations of each other seen from different frames of reference, and so the physics and analysis techniques can be used for both types.

If considered from a frame of reference which moves with the wave front, this is amenable to the same analysis as a stationary jump.

[16] As is true for hydraulic jumps in general, bores take on various forms depending upon the difference in the waterlevel upstream and down, ranging from an undular wavefront to a shock-wave-like wall of water.

[9] Figure 3 shows a tidal bore with the characteristics common to shallow upstream water – a large elevation difference is observed.

Figure 4 shows a tidal bore with the characteristics common to deep upstream water – a small elevation difference is observed and the wavefront undulates.

When this occurs, the water slows in a rather abrupt rise (a step or standing wave) on the liquid surface.

[17] Comparing the characteristics before and after, one finds: The other stationary hydraulic jump occurs when a rapid flow encounters a submerged object which throws the water upward.

Analysis shows: The height of the jump is derived from the application of the equations of conservation of mass and momentum.

is the dimensionless Froude number, and relates inertial to gravitational forces in the upstream flow.

Such standing waves, when found downstream of a weir or natural rock ledge, can form an extremely dangerous "keeper" with a water wall that "keeps" floating objects (e.g., logs, kayaks, or kayakers) recirculating in the standing wave for extended periods.

In the design of a spillway and apron, the engineers select the point at which a hydraulic jump will occur.

Obstructions or slope changes are routinely designed into the apron to force a jump at a specific location.

If the apron slope is insufficient to maintain the original high velocity, a jump will occur.

Two methods of designing an induced jump are common: In both cases, the final depth of the water is determined by the downstream characteristics.

Macro-scale vortices develop in the jump roller and interact with the free surface leading to air bubble entrainment, splashes and droplets formation in the two-phase flow region.

[15][16] A number of variations are amenable to similar analysis: Figure 2 above illustrates an example of a hydraulic jump, often seen in a kitchen sink.

For laminar jets, the thin film and the hydraulic jump can be remarkably smooth and steady.

In 1993, Liu and Lienhard demonstrated the role of surface tension in setting the structure of hydraulic jumps in these thin films.

[27] A 2018 study[28] experimentally and theoretically investigated the relative contributions of surface tension and gravity to the circular hydraulic jump.

To rule out the role of gravity in the formation of a circular hydraulic jump, the authors performed experiments on horizontal, vertical and inclined surfaces finding that irrespective of the orientation of the substrate, for same flow rate and physical properties of the liquid, the initial hydraulic jump happens at the same location.

They proposed a model for the phenomenon and found the general criterion for a thin film hydraulic jump to be where

The internal hydraulic jumps have been associated with salinity or temperature induced stratification as well as with density differences due to suspended materials.

[31] A hydraulic jump also occurs at the tropopause interface between the stratosphere and troposphere downwind of the overshooting top of very strong supercell thunderstorms.

[32] A related situation is the Morning Glory cloud observed, for example, in Northern Australia, sometimes called an undular jump.

[16] The hydraulic jump is the most commonly used choice of design engineers for energy dissipation below spillways and outlets.

Even with such efficient energy dissipation, stilling basins must be carefully designed to avoid serious damage due to uplift, vibration, cavitation, and abrasion.

[7][8][13][15] While travelling down river, kayaking and canoeing paddlers will often stop and playboat in standing waves and hydraulic jumps.

The standing waves and shock fronts of hydraulic jumps make for popular locations for such recreation.

Hydraulic jumps have been used by glider pilots in the Andes and Alps[31] and to ride Morning Glory effects in Australia.

Figure 1: A raft encountering a hydraulic jump on Canolfan Tryweryn in Wales
Figure 2: A common example of a hydraulic jump is the roughly circular stationary wave that forms around the central stream of water. The jump is at the transition between the area where the circle appears still and where the turbulence is visible.
Figure 3: A tidal bore in Alaska showing a turbulent shock-wave-like front. At this point the water is relatively shallow and the fractional change in elevation is large.
Figure 4: An undular front on a tidal bore. At this point the water is relatively deep and the fractional change in elevation is small.
Figure 5: Series of roll waves moving down a spillway, where they terminate in a stationary hydraulic jump
Naturally occurring hydraulic jump observed on the Upper Spokane Falls north channel
Illustration of behaviour in a hydraulic jump
Burdekin Dam on the Burdekin River in Queensland , Australia showing pronounced hydraulic jump induced by down-stream obstructions and a gradient change
Saint Anthony Falls on the Mississippi River showing a pronounced hydraulic jump
Supercritical flow down the Cleveland Dam spillway at the head of the Capilano River in North Vancouver, British Columbia , Canada
Energy dissipation using hydraulic jump
Kayak playing on the transition between the turbulent flow and the recirculation region in a pier wake